Review of Low Vision Rehabilitation

8/7/2019 Review of Low Vision Rehabilitation

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Review of Low Vision Rehabilitation

Mark E. Wilkinson, OD

Contents

Introduction What is Low Vision Rehabilitation? Definitions Codes for Low Vision Rehabilitation Diagnoses and Procedures Other Vision Impairment Classification Systems Epidemiology of Visual Impairment Rehabilitation Approach to Low Vision The Low Vision Rehabilitation Examination Comprehensive Case History Determination of the Patient's Vision Enhancement Needs The Examination Sequence Determination of Refractive Errors Visual Function Tests Health Assessment Applicability of Selected Low Vision Devices Magnification Vision Rehabilitation Devices Rehabilitation Instruction Report Writing Low Vision Practice Management Considerations

Conclusion References Appendix: Computer Software Available for Low Vision Patients

Introduction

Blindness and vision impairment represent a significant burden, not only to those affected by sight loss, butalso to our national economy. It is estimated that $468 billion is spent annually on care and services for the

blind and visually impaired in the US. (Source: Testimony, National Alliance for Eye and Vision Researchbefore the Labor, Health and Human Services, Education and related Agency Sub-Committee of the Houseof Representatives Appropriation Committee, March 2005)

Based on this testimony, it should be clear that helping individuals who are visually impaired to function attheir highest potential will allow many to remain independent, which will directly impact the personal andeconomic/social burden vision loss causes.

What is Low Vision Rehabilitation?Low vision rehabilitation is the management of individuals who have a congenital or acquired impairment ofvisual acuity, visual field, and/or other functional vision factors. This loss of vision can interfere with the

process of learning, vocational or avocational pursuits, social interaction, and activities of daily living. Mostimportantly, the impairment of vision cannot be adequately improved by conventional refractive measures.Low vision rehabilitation involves a continuum of care, which begins with medical and surgical interventionand proceeds through to the prescription of low vision devices and vision rehabilitation services.
http://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#introhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#Whathttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#Definitionshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Codeshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Otherhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Epidemiologyhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg3.cfm#Rehabilitationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg3.cfm#Thehttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg4.cfm#Comprehensivehttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg4.cfm#Determinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg5.cfm#Examinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg6.cfm#Determinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg6.cfm#Visualhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Healthhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Applicabilityhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Magnificationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg8.cfm#Visionhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Rehabilitationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Reporthttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Lowhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Conclusionhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Referenceshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Appendixhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#introhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#Whathttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg1.cfm#Definitionshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Codeshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Otherhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg2.cfm#Epidemiologyhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg3.cfm#Rehabilitationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg3.cfm#Thehttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg4.cfm#Comprehensivehttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg4.cfm#Determinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg5.cfm#Examinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg6.cfm#Determinationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg6.cfm#Visualhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Healthhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Applicabilityhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg7.cfm#Magnificationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg8.cfm#Visionhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Rehabilitationhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Reporthttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Lowhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Conclusionhttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Referenceshttp://www.pacificu.edu/optometry/ce/courses/15911/lvrpg9.cfm#Appendix


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Codes for Low Vision Rehabilitation Diagnoses and Procedures

The conditions requiring low vision rehabilitation services are specified using the usual ICD-9 codes. Inaddition, for compensation for low vision rehabilitation services, another standard set of diagnostic and

procedure codes is used.

The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) is based onthe World Health Organization's Ninth Revision, International Classification of Diseases (ICD-9). ICD-9-CM is the official system for assigning codes to diagnoses and procedures associated with hospitalutilization in the United States. (http://www.cdc.gov/nchs/about/otheract/icd9/abticd9.htm)

The set of codes used for specifying the degree of a patient's visual acuity impairment is based on the ICD-9Classification of Visual Acuity Impairment designating medical necessity for rehabilitation:

Moderate Impairment: 369.16-369.25; Best corrected acuity less than 20/60 (6/18) Severe Impairment: 369.12-369.22 (legal blindness); Best corrected acuity less than 20/160 (6/48) or

visual field less than or equal to 20 degrees Profound Impairment: 369.06-369.08; Best corrected acuity less than 20/400 (6/120) or visual field

less than or equal to 10 degrees Near Total Impairment: 369.01-369.04; Best corrected acuity less than 20/1000 (6/300) or visual

field less than or equal to 5 degrees Total Impairment: no light perception

Impairment can also take the form of visual field loss. Field loss codes and definitions from the ICD-9Classifications of Visual Field Loss designating medical necessity for rehabilitation are as follows:

368.4: scotoma involving the central area (within 10 degrees of fixation) 368.45: generalized contraction or constriction 368.46: homonymous bilateral field defects 368.47: heteronymous bilateral field defects

Along with disease codes, the ICD-9 classification codes for visual acuity and visual field loss should beused when billing Medicare, Medicaid, or other insurance providers so as to better demonstrate the need foryour services.

Other Vision Impairment Classification SystemsWhat follows are classifications for describing visual acuity or visual field loss that avoid the use of the termlegally blind and are designed to give be a better description of the vision loss.

The WHO Classification of Visual Acuity Loss provides the following definitions and acuity ranges:

Normal acuity: 20/25 (6/7.5) or better Mild vision loss : 20/32 (6/9.6) to 20/63 (6/18.9) Moderate vision loss: 20/80 (6/24) to 20/160 (6/48) Severe vision loss: 20/200 (6/60) to 20/400 (6/120) Profound vision loss: 20/500 (6/150) to 20/1000 (6/300) Near blindness: less than 20/1000 (6/300) Blindness: no light perception

American Medical Association's Classification of Visual Field Loss (Based on the American MedicalAssociation's Guide to the Evaluation of Permanent Impairment, 5th Edition, Chapter 12 - The Visual


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System American Medical Association's Guide to the Evaluation of Permanent Impairment, 5th Edition,Chapter 12 - The Visual System) provides the following definitions and usable remaining field ranges:

Normal: 120 degrees or better of usable field Mild vision loss: 80 to 119 degrees of usable field Moderate vision loss: 21 to 79 degrees of usable field Severe vision loss: 16 to 20 degrees of usable field Profound vision loss: 8 to 15 degrees of usable field

Near blindness: 1 to 7 degrees of usable field Total vision loss: no light perception

Epidemiology of Visual ImpairmentVision loss is a common problem as we age. The estimated number of individuals who are visually impairedin the US varies from 3.5 to 14 million, depending on which definition of visual impairment is used.

In 1995, the Lighthouse National Survey on Vision Loss estimated the following:

13.5 Million Americans 45 years of age and over (1 in 6) say they are visually impaired. For Americans age 75 and older, 1 in 4 say they are visually impaired.

Risk factors for developing visual impairment include:

Aging: Vision Problems in the United States (VPUS) states The leading causes of visionimpairment in the US are primarily age-related eye disease. By the year 2030, the number ofindividuals over the age of 60 will double.

Age-Related Macular Degeneration: VPUS says over 1.6 million Americans, age 50 and older, havelate AMD, which they define as dry AMD where atrophy exists, and all cases of wet AMD.

Cataracts: VPUS says 20.5 million Americans, age 40 and older, or 1 out of 6 in this age range. Byage 80, 1out of 2, or half, have cataracts

Diabetic Retinopathy: VPUS says 5.3 million Americans, age 18 and older, or 2.5% of thispopulation have diabetic retinopathy (this includes those with mild or worse retinopathy, includingnon-proliferative retinopathy, macular edema, or proliferative changes).

Glaucoma: VPUS says 2.2 million Americans, age 40 and older, or 1.9% of this population hasglaucoma.

Race: VPUS reports that diabetic retinopathy is more common in Whites, prior to age 40, and morecommon in Hispanics later in life; Glaucoma is more common in Blacks and Hispanics than Whites.


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Rehabilitation Approach to Low VisionLow vision care is no longer just about prescribing optical or electronic devices. Maximizing the potential ofindividuals with vision loss requires a much larger scale and integrated rehabilitative approach. For thisreason, it is important to understand the following definitions of terms commonly used in rehabilitation:

Disease/Disorder:

Any deviation from the normal structure and/or function, Describes organ disease and etiology, and Refers to anatomical changes in the visual organs caused by diseases of the eye, such as macular

degeneration, diabetic retinopathy, glaucoma, cataracts and optic atrophy, etc.

Impairment:

Manifestation of organ dysfunction or disease, Based on the severity and duration of the disease, and Refers to the functional loss that results from a visual disorder.

Abnormality in visual system functioning includes difficulties with:

Visual Acuity, Visual Field, Binocularity, Color Perception, Contrast Sensitivity, and Dark Adaptation.

Medical/Surgical Services:

The aim of these services is to diagnose and treat diseases/disorders in an attempt to reverse and/orlimit the impairments severity.

Disability:

Produced by severe and chronic impairments Loss of the skills/abilities of the individual to perform desired, usual, and necessary activities.

Visual Disability results in reduced ability for:

Reading and Writing, Mobility, including driving, Activities of daily living, and Vocational activities.

Handicap:

Barrier to normal functioning in society Depends on the severity and duration of a disability Develops when limitations imposed by the disability combine with constraints imposed by society

and the environment Refers to the ensuing psychosocial and economic consequences of a visual loss, such as the loss of

independence or the inability to work


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Rehabilitation:

Rehabilitation is a process designed to influences the links between disability and handicap so that agiven disorder results in the least possible handicap. It can involve the relearning of vocational and/ordaily living skills already acquired before the onset of visual disability. It may require the use ofadaptive equipment and techniques.

Low Vision Rehabilitation Services:

This term refers to the full range of clinical and instructional services related to the prescribing andtraining to facilitate the use of optical, electronic and non-optical devices with the remaining vision.

Habilitation Services:

This term refers to the education and development of children and youth with congenital or earlyonset visual disabilities. These services can include the teaching of compensatory and other visualefficiency skills as well as daily living skills.

Human Services:

These services assess disabilities and to diagnose and treat handicaps by providing special education,vocational and support services as well as environmental alteration. Human services providers alsocreate legal provisions for and exceptions to societal requirements and expectations.

This table illustrates the use of rehabilitative terms for two specific conditions. It is important to note that anindividual with 20/50 (6/15) vision may feel terribly disabled or handicapped whereas an individual with20/200 (6/60) vision may not feel at all disabled or handicapped at all.

Disorder Impairment Disability Handicap

Age-Related MacularDegeneration

Decreased visualacuity

Cannot read roadsigns

Loss of drivers license

GlaucomaDecreased visualfield

Orientationproblems

Loss of ability to travelindependently

The Low Vision Rehabilitation ExaminationNow that a set of commonly agreed upon definitions have been established, the low vision examination canbe presented.

The low vision exam is a structured process to be followed in a sequential manner when evaluatingindividuals who are visually impaired. It is important to note that the visual needs and functioning of theindividual cannot be predicted based on the diagnosis or distance visual acuity alone. Individual variationsmake it impossible to generalize a rehabilitation/treatment plan for a given diagnosis or visual acuity levels.It must also be emphasized that there is no single device that works best for a given diagnosis or acuity level.

The components of the structured low vision examination are as follows:

Comprehensive case history Determination of the patient's visual enhancement needs

The examination/refraction sequence Visual function tests


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Health assessment Determine applicability of selected low vision devices Determine needed magnification for devices Report preparation

These components will be discussed individually.


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Comprehensive Case HistoryThis is the most important aspect of the examination. It includes the following components:

Ocular history and current status Health history and current status Developmental history Review functional vision ability (pediatric evaluation if appropriate)

Educational history Functional task analysis Devices used in the past Working distance requirements Specific needs or goals as stated by the patient Specific needs or goals as identified by the employer, teacher, family or caregiver Specific needs as determined by the history Establish realistic patient goals (an ongoing process continuing during the course of the examination)

and exploration of rehabilitation options

During history taking, it is important to determine what types of visual difficulties your patient is

experiencing because of their vision loss. There are many difficulties above and beyond reading or drivingthat may need to be explored. This is why a comprehensive history is so important.

Patients should also be asked about the occurrence of Charles Bonnet Syndrome in which formed, non-psychotic hallucinations of people, animals, etc. are seen by about 10 to 20% of patients with vision loss.Management of this syndrome includes physician recognition, empathy, reassurance, and patient education,which form the cornerstone of treatment. For this reason, consider initiating a discussion on Charles Bonnet

by saying the following: I often find that patients with a loss of vision experience phantom visions perhaps streaks, flashes, or even faces or scenerythat seem unusual or hard to understand. Have you

noticed anything like that?

It should also be noted that depression is common among the elderly in general and is even more commonamong those who have experienced a significant loss in vision. This depression can be severe enough so asto require medical intervention to reduce the probability of self-destructive acts.

Ocular history should include a classification of vision loss. (Source: E. E. Faye, MD) Knowing the cause ofyour patients vision loss is important because it will help direct your examination and assist in the selectionof devices that will be demonstrated to the patient. This is because each eye disease has a predictable effecton function, and the type and severity of the disease influences the ultimate effectiveness of anyintervention.

The causes of visual impairment can be defined by the location of the pathology affecting the visual system:ocular media, retina, and/or brain.

Vision loss can be classified as: overall blur with no field defect, central field defect, and peripheral fieldconstriction. The causes and management strategies for each classification will be discussed separately.

Overall Blur with No Field Defect. This condition typically occurs when the refractive media (cornea, pupil,lens or vitreous) become cloudy. In many cases of cloudy media, the individuals complaint often seems outof proportion to their measured distance visual acuity. This is usually due to a significant change in theircontrast sensitivity.There are a variety of medical conditions that can cause this type of vision loss.

They include:


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o Corneal dystrophy

o Corneal scarring

o Keratoconus

o Optic atrophy

o Albinism

o Aniridia

o Nystagmus

o Cataracts

o Diabetic retinopathy/macular edemao Achromatopsia

o Vitreous hemorrhage

o Amblyopia

o Central serous retinopathy

o Macula problems with impaired central resolution without scotoma can be caused by:

Aplasia

Edema Amblyopia

When there is overall blur with no field loss, the patient will typically report these symptoms:

Blurred or hazy distance/reading vision Decreased contrast Glare sensitivity Fading of colors

However, there will be little effect on the following:

Peripheral vision Independent travel abilities

Central Field DefectThis condition can occur from a variety of medical conditions including:

Macular degeneration Cystoid macular edema Ischemia Diabetic macular edema Toxoplasmosis/histoplasmosis Optic nerve diseases Macular Cyst - Hole Photocoagulation

Trauma/Drugs Retinal vascular diseases

Patients with central field defects will often report the following symptoms:

Blurry/hazy vision Central distortion Scotomas at or near the fixation point Reading problems Difficulty recognizing faces Reduced detail/contrast loss Color vision changes


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However, the following will not typically be affected:

Peripheral vision Independent travel abilities

Peripheral Field ConstrictionMedical conditions that can cause peripheral field loss include thefollowing:

Retinitis pigmentosa Glaucoma Optic nerve disease Extensive laser treatments Stroke/traumatic brain injury/brain tumor Diabetic retinopathy Multiple sclerosis Retinopathy of prematurity Retinal detachment

Patients with peripheral field constriction will often report the following:

Difficulty with visual orientation in space Reduced night or dim light vision Limited response to magnification Reduced contrast sensitivity

This function will probably not be affected in peripheral field loss:

Central visual acuity, but detail vision may or may not be fully retained

Health history should include a general health review and a discussion of all medications currently andrecently taken by the patient. Information on hearing/other impairments/conditions, orthopedic limitations,and self-care needs (e.g., ileostomy, diabetes) should also be obtained.

Specific questions about any co-morbidities such as the following should be asked:

Diabetes type, duration, treatment, control HIV/AIDs stage, treatment Arthritis which might limit mobility or produce significant discomfort Neurological conditions such as:

o Multiple sclerosis

o

Cerebral palsyo Stroke

o Traumatic brain injury

Determination of the Patient's Vision Enhancement NeedsAn extensive discussion regarding enhancement needs should focus on what may be very differentrequirements for distance, intermediate, and near tasks. Mobility, occupational, recreational, and daily livingconcerns should be explored in depth.


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The Examination SequenceThe low vision examination should include the following steps:

Review previous spectacles Distance visual acuity Near visual acuity/working distance Refraction (trial frame in most cases)

Visual function tests Ocular health assessment Determine low vision aid needs and required magnification Rehabilitation instruction

Selected aspects of the examination sequence will be discussed in detail.

Visual Acuity Assessment

After history taking, the next most important task in the care of visually impaired individuals is accurateassessment of visual acuity.

Visual acuity (VA) testing should accomplish the following:

Measure spatial resolving capacity (ability to see fine detail) of the visual system Allow for quantification of high contrast vision loss Monitor stability or progression of disease and visual abilities as rehabilitation progresses Allow assessment of eccentric viewing postures and skills, patient motivation, and scanning ability

(for field loss) Allow teaching of basic concepts and skills (e.g., eccentric viewing) Provide the basis for determining initial magnification requirements Verify eligibility for tasks such as driving Verify eligibility for services as a "legally blind" patient Note that inaccurate acuity testing typically underestimates the patient's ability

Factors to consider when measuring VA include:

Contrast of chart Lighting Number of optotypes at each acuity level Spacing of targets Difficulty of targets used (e.g., letters, numbers, pictures) Single letter targets versus words (or multiple digits) versus continuous text

Eccentric viewing postures Expressive as well as receptive language skills and cognitive level of the task

Types of Visual Acuity Testing

Acuity can be assessed by the ability of the patient to localize, detect, resolve, and/or recognize test stimuli.

Localization Acuity is the visual awareness/perception of the location of an object or light. Examplesinclude light perception with projection, and awareness of location of people/animals/objects.

Detection Acuity , also know as Minimum Perceptible Acuity, measures detection discrimination.Minimum perceptible acuity is concerned with simple detection of objects, not their identification ornaming. An example of this type of acuity testing involves determining whether a child can see and

grasp a small candy bead held in the examiner's hand.


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Resolution Acuity , also know as Minimum Separable Acuity, measures the threshold at which anindividuals can discriminate the separation between critical elements of a stimulus pattern (e.g.,smallest visual angle at which two separate objects can be discriminated). The Landolt C test andgrating acuity are examples of minimum separable tasks.

Recognition Acuity , also know as Minimum Legible Acuity, measures the individual's ability torecognize progressively smaller objects (e.g., letters, numbers or objects) called optotypes. The anglethat the smallest recognized letter or symbol subtends on the retina is a measure of visual acuity. Thistype of acuity testing is used most often clinically.

Snellen Acuity (Herman Snellen, MD 1862) uses a notation in which the numerator is the testingdistance (in feet or meters) and the denominator is the distance at which a letter subtends the standardvisual angle of 5 minutes. A 20/20 letter (6/6 in meters) subtends an angle of 5 minutes when viewedat 20 feet (6 meters).

Using the correct chart will provide the most accurate assessment of visual acuity. Commonly used lowvision charts include Feinbloom and Bailey-Lovie type charts.

The Feinbloom number chart (available from Designs for Vision, Inc.) has the following characteristics:

It presents high contrast numbers It has an irregular progression of target sizes and task difficulty It has a large acuity range (20/10 to 1/700) (6/3 to 6/210) It is a movable flip chart that can be used at any distance

Figure 1. This is an example of an optotype from the Feinbloom number chart.


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The ETDRS/Bailey-Lovie chart(available from the Lighthouse International or the UC Berkley Optometry

School) has the following characteristics:

It presents high contrast letters It uses a logarithmic progression of target sizes (each larger line is 0.1 log units or 1.26 the size of the

previous line) It has proportional spacing of letters and rows which results in the task demand remains constant at

different distances

It can be used at 1, 2, and 4 meters

Figure 2. The ETDRS/Bailey-Lovie chart.

TheStandard Snellen charthas the following characteristics:

It presents an irregular progression of target sizes and task difficulty (e.g., no targets between 20/100(6/30) and 20/200 (6/60) and between 20/200 (6/60) and 20/400 (6/120))

It can be adapted for low acuity levels by moving the patient closer to the chart Most Snellen charts are projected so letters are shadows, which results in lower contrast than is

possible on printed charts Clarity of charts can vary depending on the ambient room illumination, age of the projection bulb,

etc.

Acuities measured by specialized low vision techniques may not correlate by simple ratio to a standard 20foot or 6-meter acuity measured with a projected chart. For example, 10/40 (3/12) does not necessarily equal20/80 (6/24) and 10/100 (3/30) does not necessarily equal 20/200 (6/60). In addition, there is not always aone-to-one relationship between different chart types.

Shorter test distances allow for greater accuracy when measuring lower levels of acuity. Typical starting testdistances are 5 to 10 feet or 2 to 4 meters, depending on the chart used. Remember to account foraccommodative demands at closer distances.

Record the visual acuity as actual test distance over size of character read. For the Feinbloom chart, the testdistance in feet becomes the numerator, and the size of the number read (noted in foot size) is the


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denominator. For example a 400 size optotype at 10 feet (10/400) (3/120) is the equivalent of an 80 sizeoptotype at 5 feet (5/80) (1.5/24).

When the ETDRS chart is viewed 1, 2, or 4 meters, use the testing distance as the numerator and the M sizeof the letters read as the denominator. M size is given in the far left column of the chart. The next column onthe chart gives the conversion to Snellen equivalent (not the letter size). For example, when testing at 2meters and the patient reads the 32M line (160 Snellen equivalent), the acuity is recorded as 2/32, which isthe numeric equivalent of 20/320.

Count fingers, hand motion, and light detection. It is important to accurately measure visual acuity todetermine if the patient's rehabilitation plan is helping. For this reason, do not use counts fingers if at all

possible. If the patient can see fingers, he or she can read the larger figures on a chart if it is brought closeenough.

If counts fingers must be used, note the distance at which the patient can count fingers. Most fingers areequivalent in size to a 20/200 (6/60) size letter. Therefore, counting fingers at 3 feet (1 meter) is equivalentto about 3/200 (1/60), which is equal to 20/1300 (6/360).If the patients visual acuity is reduced to the point at which he or she can only see hand motions, note inwhich quadrant(s) and at what distance the motions can be seen. If the patient can only see light, determine ifhe or she has light perception with projection versus just light perception. If direction can be

determined, note in which quadrant(s) and at what distance the light can be seen.

Pinhole Visual Acuity For individuals who do not have any type of ocular disease, a pinhole aperture can bea useful tool for determining if a refractive error is present or if a refractive correction change is needed. Themost useful pinhole diameter for clinical purposes is 1.2 millimeters. This size pinhole will be effective forrefractive errors of plus to minus 5.0D.A pinhole improves visual acuity by decreasing the size of the blur circle on the retina resulting in animprovement of the individual's visual acuity. However, if the pinhole aperture is smaller than 1.2millimeters, the blurring effects of diffraction around the edges of the aperture will actually increase the blurcircle, causing the vision to be worse.

Individuals with macular disease, as well as those with other ocular diseases that affect central vision, mayhave similar or even reduced acuity when looking through a pinhole. This is because the reduced amount oflight entering through the pinhole makes the chart less easy to read. Additionally, it can be difficult to use aneccentric fixation point through a pinhole. For this reason, individuals with ocular disease should not be toldthat a spectacle correction change will not improve their vision, based solely on their looking through a

pinhole. Careful retinoscopy along with a trial frame refraction (in most cases) is needed to determinewhether an individual with pathology induced vision loss will benefit from a spectacle correction change.During measurement of visual acuity, the clinician should evaluate any eccentric viewing techniques used bythe patient.

Near Acuity Measurement For measuring visual acuity at near, charts designed for individuals who arevisually impaired (i.e., charts with single letters, isolated words, or short sentences) should be utilized andtesting distances must be measured and recorded.Use of the M system is preferred for specifying near acuities because it yields a Snellen fraction that is moreeasily compared to distance visual acuities. The designation of letters signs (e.g., 1M, 2M) indicates thedistance in which the print is equivalent in angular size to a 20/20 optotype. For example, 1M print subtends5 minutes of arc at 1 meter.

There are a variety of cards that can be used for assessing near visual acuity.The M unit chart was developed by Bailey in 1978. The International Council of Ophthalmology as well asthe International Society for Low Vision Research and Rehabilitation recommends metric acuity testing,

because it is the most accurate and reproducible test available.The Lighthouse near chart uses Sloan optotypes that range in size from 8M to 0.3M.


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Figure 3. The Lighthouse Near Acuity chart.

The ETDRS near chart, like distance version, has a logarithmic progression in optotype sizes, with

proportional spacing of letters and rows. This allows the task to remain constant at different distances.

The Lighthouse Game and Number cards present words and triple digit numbers. This allowsassessment of crowding factors as well as cognitive influences on reading ability. These are the cards mostcommonly used by the author for evaluating near vision.

Figure 4. Lighthouse Game card. Figure 5. Lighthouse Number card.


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The Bailey-Lovie word reading chart presents logarithmic progression of unrelated words.The MN Read charts present sentences.

Figure 6. The MN Read chart.

Sloan Continuous Text reading cards provide a more accurate measure of reading ability than do singleoptotype acuity cards.

Figure 7. Sloan Continuous Text reading cards.

Jaeger Acuity. This is the least desirable letter-size designation (Source: International Council ofOphthalmology and the American Academy of Ophthalmology). Jaeger numbers are a printers designationthat refers to the boxes in the print shop in Vienna where Jaeger selected his print samples in 1854. The print


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box numbers were are not proportional to the letter sizes, and the system has never been standardized. Inaddition, print size is not the same from one Jaeger test card or chart to another

Recording Near Acuity Near visual acuity is typically recorded as testing distance in meters over M-sizeletter read, thus yielding a true Snellen fraction. For example, if a 4M letter is read at 40 cm, the acuity isrecorded as 0.40/4M, which is equivalent to 20/200 (6/60) distance acuity. As a second example, if a 1.6Mletter is read at 20 cm, the acuity is recorded at 0.20/1.6M, which is equivalent to 20/160 (6/48) distanceacuity

Use of the M system also facilitates calculation of addition power (i.e., the dioptric power required to focusat a specific metric distance). For example, if a patient reads 0.40/4M and wants to read 1M print, he or shemust hold the material at distance X where X is determined by the equation 0.40/4M = X/1M. Solving theequation for X yields X = 0.10M or 10cm. The lens that focuses at this distance is +10D. This will bediscussed more fully later in the course.


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Determination of Refractive Errors

The goal of a subjective refraction is to achieve the best possible clear and comfortable binocular vision. Theability of the clinician to maintain patient control during the refraction is directly related to his or her abilityto communicate clearly and directly.There are many disadvantages to using a phoropter for refractive error determination. These include:

The light reflex for retinoscopy is poorer than with loose lenses There is decreased light transmission when multiple lenses are used in a phoropter Eccentric viewing is difficult or impossible with a phoropter It is difficult for patients with nystagmus to use their null points with a phoropter It is difficult to use Just Noticeable Difference (JND) refraction techniques with a phoropter

Conversely, there are many advantages to using a trial frame for refractive error determination. Theseinclude:

A trial frame and loose lenses are easier and more natural than a phoropter for patients who aredifficult to refract or who are visually impaired

Standard refraction techniques are employed when performing a trial frame refraction just as for anindividual with normal sight

Just Noticeable Difference refraction techniques are used for individuals whose visual acuity is lessthan 20/50 (6/15)

As a bottom line, when in doubt use the trial frame

Just Noticeable Difference (JND) Refraction Techniques

The JND is the amount of lens power needed to elicit an appreciable change in clarity or blur; the poorer thevisual acuity, the larger the JND will be. Numerically, the JND in diopters equals the denominator of the 20

foot Snellen acuity divided by 10. For example, for a 20/150 Snellen letter, 150 divided by 10 equals 1.50D.The patient would have an initial range of clarity of plus and minus 0.75D around their best correction. (Thiscalculation also works for metric notation.)JND techniques allow accurate refraction at any acuity level, the techniques apply to both sphere andcylinder corrections, and JND techniques elicit reliable answers.As an example of JND refraction to determine sphere power, consider the following patient:

VA is 20/400, no old spectacles, and unable to do retinoscopy 400/10 provides a JND of 4.00D. Start with +/-2.00D JND steps Patient states +2.00D is clearer. Put +4.00D in the trial frame With +4.00D in the trial frame, again asked the patient to compare +2.00D/-2.00D around this value.

If the patient still prefers +2.00D over the +4.00D lens, replace the +4.00D lens in the trial framewith a +8.00D lens.

With +8.00D in the trial frame, again asked the patient to compare +2.00D/-2.00D over the +8.00Dlens. If the patient now prefers -2.00D, replace the +8.00D lens in the trial frame with a +6.00D lens.

Now refined with +1.00D and -1.00D bracketing lenses Eventually, fine tune if possible with +0.50D and -0.50D lenses


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Figure 8. Determining sphere power using the JND method.

Finding the best cylinder axis and power requires using a Jackson Cross Cylinder (JCC) with the appropriatevalue the same JND technique described above:

For 20/50 (6/15) or better vision, use a +/-0.25D JCC For 20/63 (6/18.9) to 20/100 (6/30), use a +/-0.50D JCC For 20/125 (6/37.5) to 20/160 (6/48), use a +/-0.75D JCC

For 20/200 (6/60) or poorer acuity, use a +/-1.00D JCC

Figure 9. Determining cylinder power using the JND method.

Here is an example of the JND technique used to determine cylinder power and axis:

After establishing the patient's spherical power as describe above, VA is 20/200 (6/60) 200/10 = 2.00D so start with a +/-1.00 JCC With the JCC oriented for power at 90/180 degrees, ask the patient which orientation is clearer


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Patient states that +1.00D axis 180 is clearer. Put a +2.00D axis 180 cylinder lens in the trial frame With a +2.00D axis 180 cylinder lens in the trial frame, again asked the patient to compare +1.00D to

-1.00D axis 180. If the patient still prefers +1.00D axis 180, replace the +2.00D axis 180 cylinderlens in the trial frame with a +4.00D axis 180 cylinder lens

With a +4.00D axis 180 cylinder lens in the trial frame, again asked the patient to compare +1.00D to-1.00D axis 180. If the patient now prefers -1.00D axis 180, replace the +4.00D axis 180 cylinderlens in the trial frame with a +3.00D axis 180 cylinder lens

Now refined with a +0.50D/-0.50D JCC.

After the cylinder power is determined, repeat the same process to determine the cylinder axis.

Final Comments on JND Refraction

Remember to decreased the power interval as visual acuity improves Use trial frame refraction when visual acuity is 20/50 (6/15) or worse, or if regular refraction

techniques are not working Remember the importance of the refraction because the only intervention needed to enhance visual

functioning might be to prescribe appropriate glasses


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Visual Function Tests

These tests are designed to provide a better understanding of an individuals quality of vision, not just thequantity number clinicians get by testing distance acuity alone. Distance acuity tells us the patient's quantityof vision, not how well they are able to use their vision, i.e., their quality of vision. Near acuity testing, alongwith the following tests, helps the clinician to better understand how vision loss has effected the patient'svisual functioning.

Visual function tests include the following:

Contrast sensitivity Amsler grid Preferred retinal locus determination Visual field Color vision Glare testing

Contrast Sensitivity Contrast indicates the variation in brightness of an object. When a vision chart usesperfectly black ink on perfectly white paper, 100% contrast is achieved. Printed acuity charts that

approximate 100% contrast are helpful for characterizing central visual acuity. However, they are lesshelpful for examining visual function away from fixation.

Figure 10. Contrast sensitivity test chart.

Contrast sensitivity is typically tested using alternating light and dark bars with varying contrasts. Thenumber of light bands per-unit width or per-unit angle is called the spatial frequency. During clinical testing,

patients are presented with targets of various spatial frequencies and contrasts. The minimum detectablecontrast is the contrast threshold. The reciprocal of the contrast threshold is defined as the contrastsensitivity, and the manner in which contrast sensitivity changes as a function of target spatial frequency iscalled the contrast sensitivity function.


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Figure 11. Contrast sensitivity recording forms showing the range of normal contrast sensitivity functions

(shaded areas).

Contrast sensitivity can be tested with sine wave gratings presented using either charts or video gratings.Because standard Snellen acuity assesses only high spatial frequency (e.g., 20/20 (6/6), which is equivalentto a grating frequency of 30 cycles per degree), they do not provide an accurate picture of the entire range ofan individual's visual functioning, particularly when the individual has an ocular disease. Snellen acuity doesnot assess mid- or low-spatial frequency contrast sensitivity.

Acuity charts provide a quantitative assessment of visual functioning whereas contrast sensitivity chartsprovide a qualitative assessment of visual functioning. Contrast sensitivity testing is similar to audiologicaltesting, which assesses an individual's ability to hear the entire range of sound frequencies.

Contrast sensitivity testing can detect changes in visual function even if Snellen visual acuity is normal. Thiscan occur when corneal pathology, cataracts, glaucoma, and various other ocular diseases are present.Contrast sensitivity testing helps to predict illumination, contrast and magnification needs as well as predictsuccess with optical magnification.

Amsler Grid Amsler grid testing is useful in low vision rehabilitation to locate and characterize scotomas,to determine if the patient is using eccentric viewing, and/or train the individual to use eccentric fixation.Amsler grid testing can also be useful for predicting an individual's success with the use of optical/electronicdevices.

A scotomas location relative to fixation, size, shape and density can all be estimated using the Amsler grid.

The location of a scotoma may have prognostic value - scotomas above the midline may have a betterprognosis for reading than scotomas to the right or directly on the midline.


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Figure 12. Amsler grid showing significant field distortion.

When using the Amsler grid, if a dense central scotoma exists but the center of grid is visible, eccentricfixation is likely. In this case, the scotoma is mapped relative to fixation, not relative to the center of thefovea. It is sometimes possible to train a patient to move his or her eyes around until the center of the Amslergrid appears. For some patients, this is easier to do this when using a video monitor.

While doing Amsler grid testing, if the grid has more distortion when viewed binocularly than it does witheither eye individually, occlusion or fogging of the worse eye may be necessary for best test results. If thegrid has less distortion when viewed binocularly than it has when viewed with either eyes alone, then

binocular devices may be more helpful.It is important during Amsler grid testing to explain and demonstrate to patients the location of theirscotomas, the concept of eccentric viewing, which eye is their dominant eye, and why they may function

better with their poorer eye occluded or fogged.

There are a number of problems with Amsler grid testing. These include the fact that the sensitivity of both

standard and threshold Amsler grid testing is very low. Almost 50% of scotomas are missed during Amslergrid testing. Larger scotomas are more likely to be detected. However, when larger scotomas are detected,the full extent of the scotoma is frequently underestimated. These problems can occur because ofunsteady/eccentric viewing and perceptual filling (visual completion).

Despite these problems, Amsler grid testing is still very useful. When Amsler grid testing shows the locationand the size of the scotoma, this information helps to predict problems the patient might have during visionrehabilitation. Additionally, it helps predict which patients will do better when viewing monocularly versus

binocularly. Finally, Amsler grid testing can provide an indication as to which patients are likely to benefitfrom eccentric viewing training. Those individuals who are able to see their scotomas and maintain a

preferred retinal locus are more likely to benefit from this training.


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Preferred Retinal Locus Determination Typically the visual systems of individuals with central scotomasnaturally, consistently, and unconsciously choose an eccentric retinal area to perform the visual task that thefovea previously performed. One study found that about 85% of patients with a central field loss were foundto have established such a Preferred Retinal Locus (PRL). For individuals with central scotomas, visual tasksare performed by aiming the eye so that the image of a visual target is placed within the PRL.

The PRL, in essence, becomes a pseudo-fovea and assumes many of the tasks of the nonfunctioning fovea.For example, object recognition and detail discrimination. Therefore, the ability of the PRL to perform

fixation, as well as pursuit and saccadic movements determines the performance ability in many activities ofdaily living. Some individuals use more than one PRL, depending on the visual task.

Under higher illumination conditions, the PRL tends to be closer to the fovea, sometimes in an area of arelative scotoma, whereas under lower illumination conditions, the PRL is switched to an area further fromthe fovea.

The relative location of one or more PRLs to a macular scotoma also indicates the degree of difficulty theindividual will have in adapting to the scotoma. Individuals with macular scotomas that encircle the PRL,(called a ring scotoma), often experience greater difficulty in activities of daily living despite having fairlygood visual acuity.

PRL testing is easily done with a scanning laser ophthalmoscope. Unfortunately, the cost of the instrumentprohibits its widespread use.

Visual Field Testing Accurately detecting peripheral and central field loss is important because visual fieldchanges can affect visual functioning. Visual field integrity is important for reading as well as forindependent travel. Visual field testing is also important for determining eligibility for services and fordriving.

Confrontation visual fields provide a quick screening which can be helpful for detecting unrecognizedperipheral defects. Confrontation visual fields can also be useful as an educational tool for patients withcentral loss by demonstrating that their peripheral vision is intact.

As opposed to automated perimetry, traditional Goldmann perimetry is easier for individuals who arevisually impaired, particularly for those with poor fixation, fatigability, and reduced visual thresholds. The

problem with this type of testing is that it requires a trained technician to perform the test.

Automated perimetry has the advantage of standardized protocols, longitudinal databases, and macularassessment capability. Additionally, this type of perimetry can be performed without a specially trainedtechnician. The problem with threshold related automated perimetry is that it tends to overestimate visualfield loss for individuals who are visually impaired. With this in mind, it is important to not rely on the

perimetry gray scale when interpreting visual field loss in individuals with inherited eye diseases or thosewith reduced central acuity. The gray scale will indicate that the visual field loss is much worse than it reallyis as compared to super-threshold visual field testing.

Color Vision Testing It is important to ask if discriminating colors is difficult for low vision patients. Notonly the patient, but also the parent/family/spouse should be asked about color discrimination difficulties.

Most acquired color vision defects are blue-yellow confusions as opposed to the typical red-green inheritedconfusions. However, many pseudoisochromatic plate tests do not detect blue-yellow problems. Also,acquired color vision loss may be monocular so eyes should be tested individually. For individuals who arevisually impaired, the Farnsworth D-15 may be the best test to use. If motor skills do not allow manipulation

of the color caps, assistance should be provided, but care must be taken to not provide clues to the properarrangement sequence when moving caps for the patient.


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It is also important to remember that inherited color vision deficiencies may also be present in individualsthat are visually impaired.

Brightness Acuity Testing (BAT)/Glare Testing It is important to ask about glare problems during historytaking. This is because routine test conditions may miss glare symptoms. Knowing about glare problems willhelp to direct lighting recommendations. Glare and poor contrast sensitivity can make management of visionloss using optical magnification difficult.


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Health Assessment

It is obviously important to review the patient's ocular and systemic health with respect to preexisting andnew diseases, and to conduct a complete ocular health examination.

When cataracts are adversely affecting visual functioning (they would normally be removed if no otherocular problems were present), and cataract surgery is not contraindicated by some other ocular disease (e.g.

active diabetic retinopathy or choroidal neovascular membrane, etc.), surgery should be considered toenhance visual functioning and maximize visual potential.

When considering postoperative refractive error correction for individuals with additional ocular diseases,Lighthouse International suggests the following: individuals undergoing cataract surgery who will requiremagnification because of coexisting conditions such as macular degeneration or diabetic retinopathy, shouldalmost never be made emmetropic postoperatively.

Lighthouse suggests that a postoperative refractive error of -2.00 D to -3.00 D will leave the individualhappier because he or she can remove his or her spectacles to read more comfortably (with or without anoptical device) than would be possible with bifocals or separate reading glasses. Additionally, if the patient

needs reading glasses, they will be of a lower power. If the patient needs higher amounts of magnification,the reading glasses will be lower powered with less weight and distortion. Additionally, patients will be ableto use hand-held magnifiers without their glasses on. Obviously, these individuals will still need a lenscorrection to have their best distance vision, but the reading advantages more than make up for this.

Applicability of Selected Low Vision Devices

Many individuals that are visually impaired will benefit from the prescription of optical and electronicdevices, and from changes in their visual environments.


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Magnification

Assuming it has been concluded that an optical aid is appropriate for a patient, the magnification to beprovided by the aid must be determined.There are 4 types of magnification that individuals with visual impairments can employ to enhance theirvisual abilities. They are: relative size, relative distance, angular, and electronic.Relative Size Magnification (RSM) enlarges an object while maintaining the same working distance.

Numerically, RSM is equal to size after magnification divided by size before magnification.

Consider an example for print:

If the original size of the print was 1M and the size after magnification is 2M, the RSM is 2x.

Because it is difficult to enlarge reading materials much beyond the 2M (18 point) level, this option is ofrelatively little value for individuals who have experienced a significant loss of vision. Additionally, thereare many things individuals who are visually impaired want to read (e.g., newspapers, mail, bank statements,etc.) that are not readily available in large print formats.

Relative Distance Magnification (RDM) The easiest way to magnify an object is to bring it closer to theeye. By moving the object, the image size on the retina is enlarged. Children with visual impairments do thisnaturally. Adults with less accommodative ability will require reading glasses to keep the object in focus asit is moved closer.

RDM is defined as r/d where r equals the reference or original working distance and d equals the newworking distance. For example:

If the original working distance is 40cm, and the new working distance is 10cm, the RDM is 40/10 or 4x.

With reading glasses, as the lens power increases, the working distance decreases. For example, a +5D lensfocuses at 100/5 = 20cm (40/5 = 8 inches) and a +10D lens focuses at 40/10 = 4 inches (100/10 = 10cm).Reading glasses do not magnify by their power alone when worn in the spectacle plane. Magnificationoccurs simply because the lens strength requires the individual using the glasses to hold things closer to havethem in focus.

Angular Magnification Angular magnification occurs when the object is not changed in position or size buthas an optical system interposed between it and the eye to make it appear larger. Examples of devices that

produce angular magnification are telescopes and hand magnifiers.

Optical Magnification Ratings

Some companies use lens focal length/4 (defined as Rated Magnification) while others use the quantity (lensfocal length/4) + 1 (defined as Conventional Magnification) to specify magnification strength for theirdevices. This is why dioptric power, which is an absolute value and is the same under all conditions, is a

better way to specify the magnification needs of an individual.

Rated Magnification (Mr)Rated magnification assumes that the individual can accommodate up to 4.00 diopters when doing closework, which gives a working distance of 25cm (25cm is the standard reference distance always used whentalking about magnification).

Conventional Magnification (Mc)


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The underlying assumption in the equation ((lens focal length/4) + 1) is that the patient is supplying oneunit (1X) of magnification

Effective Magnification (Me)Effective magnification is based on the reference distance in meters to the object (image is formed atinfinity). (d is reference distance and F is dioptric power of the lens)

If d = 25cm, then effective magnification equals F/4

If d = 40cm, then effective magnification equals F/2.5

Determining Needed Magnification Magnification needs are based on an initial reference value and thedesired final value. Clinically, needed magnification is defined as the entrance distance (or near) acuitydivided by the goal acuity (VA entrance/VA goal).

Electronic Magnification is magnification that can be provided by a closed circuit television system orcomputer software. These systems can make an image appear larger and with greater.

Magnification Estimation Techniques Accurate near visual acuity testing is essential for determiningmagnification needs required for reading and other near point activities. There are several ways to determine

a starting point for near magnification. We will discuss the two most common ones that are used today.

Kestenbaums Rule To determine the power necessary to read 1M size print (newsprint), take the reciprocalof the patient's distance acuity to establish a starting add power.As examples:

An acuity of 20/50 (6/15) inverts to 50/20 (15/6), which yields a +2.50D add 20/200 (6/60) inverts to 200/20 (60/6), which yields a +10.00D add 20/400 (6/120) inverts to 400/20 (120/6), which yields a +20.00D add

However, because distance acuity is a poor predictor of near visual functioning, this is not a very accuratemethod for determining a reading add power. The more accurate and more frequently used approach is theLighthouse method.

Lighthouse Add Determination To determine the power needed to read 1M print, measure the patient's nearacuity at a 16 inch/40 cm working distance (WD). Multiply the M acuity by 2.50D to arrive at the theoreticaladd power needed to read 1M printAs examples:

If the patient can read 4M print at 40cm (16 inches), multiply 2.50D times 4 to get a +10.00D addpower that will be required to read 1M print

If the patient can read 2M print at 40cm (16 inches), multiply 2.50D times 2 to get a +5.00D addpower that will be required to read 1M print

The Lighthouse method establishes a good starting power. However, patients may need additional power iftheir contrast sensitivity is reduced, if they have multiple scotomas, if they need to read smaller than 1M

print, or if they have less than ideal illumination when reading. The clinician should adjust the add powerusing normal reading materials under task lighting to determine how much add power is actually needed.


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Vision Rehabilitation Devices

Devices should be considered and presented to the patient in a sequence that roughly follows increasing costand complexity:

Regular spectacles Spectacle magnifiers

Absorptive lenses Hand/Stand magnifiers Telescopes Telemicroscopes Absorptive lenses Desk-top video magnifiers Head-borne video magnifiers Non-Optical devices

Regular spectacles Always start by determining whether a change in the spectacle correction will enhancedistance and/or near acuity as determined by a trial frame refraction. Regular spectacles can provide:

Distance acuity improvement Assistance with near/intermediate tasks for which lower magnification is required The dioptric power required for use with optical devices. It is important to remember that stand

magnifiers require accommodation or add power, and have maximum add limitations Clear vision for use with video magnification systems, which may require accommodation or add

power for the working distance

Stronger bifocal corrections will be required to use relative distance magnification early in the vision lossprocess. As higher amounts of reading addition are needed (greater than 6D), a +4.00D add may provebeneficial as an intermediate distance add. Individuals benefiting from this type of intermediate correctionare those who need lower amounts of magnification for less detailed tasks such as signing their name,cutting their finger nails, seeing the food on their plate as well as cooking and reading larger print, such asthe headlines, etc.Spectacle Magnifiers can take several forms. These can include:

Prismatic half eye readers (+4.00 to +12.00D with base-in prism) High plus aspheric readers (+10.00 to +20.00D) Microscopic spectacles with 2x (8D) to 12x (48D) in aspheric or doublet design Specialty microscopic spectacles in powers to 80D, which are available in doublet lens systems,

wide-angle microscopic lenses, and high-add bifocals.

Press on adds, which are available as 22mm bifocal segments in powers from 8 to 40D Clip-on and head-borne loupes, which are also available in various powers


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Figure 13. Reading spectacle designs.

When prescribing reading spectacles, is important to consider whether the patient functions bettermonocularly or binocularly. If patient is monocular, he or she will not need prism incorporated into thereading spectacles but it may be necessary to occlude/fog the fellow eye if it interferes with the better eye.

The need for occlusion or fogging the poorer seeing eye is often found in situations where thesighting/dominant eye has the greatest vision loss. In this situation, the now poorer seeing/dominant eyeconfuses the better seeing non-dominant eye resulting in poorer visual performance. Occlusion or fogging ofthe poorer seeing eye will ameliorate this problem and allow the individual to function at the highest

potential.

For those individuals who have similar near acuities between their two eyes and whose binocular acuity isbetter or the same as their monocular acuity, base-in prism will provide more comfortable, sustained readingability. Base-in prism is used for adds of +4.00 to +12.00D. The prism power equals the add strength plus 2

prism diopters base-in for each eye. As an example, a +6.00D add would have 8 prism diopters base-inadded to each eye's lens.Advantages of spectacle magnifiers:

Frees the hands for manipulative tasks Provides widest field of equivalently powered optical options Allows greater reading speed of equivalent powered reading options (once adapted) Makes binocular vision possible up to approximately a 10.00 diopter add equivalent More cosmetically acceptability to some individuals than other options Portable and relatively inexpensive

Disadvantages of spectacle magnifiers:

Requires closer working distance and may obstruct illumination


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May be inconvenient for spot reading tasks in which information is gained from single words or shortphrases (e.g., price tags)

Fixed optical center may reduce effectiveness when using eccentric fixation Makes writing difficult if lens add is stronger than 10.00 diopters

Working distance for these lenses is determined by taking the reciprocal of the equivalent add power (+20Dlens will have a working distance of 100/20 = 5cm).

Figure 14. Close working distance resulting from use of a high dioptric power lens.

Training considerations for spectacle magnifiers:

Establish the correct focal distance Difficulties with establishing the correct focal distance will notget better with practice. For this reason, it may be helpful to start with large print so blur can be moreeasily appreciated when out of focus

Evaluate and recommend appropriate lighting Individuals should be told to close their eyes or look over the top of the glasses when looking up

from reading material so as to avoid dizziness Materials should be held flat to maintain the correct focal distance for higher-powered corrections.

Some individuals may find it easier to move materials from right to left rather than moving theirheads

Practice over time is critical for success with high add spectacle mounted lenses

Absorptive Lenses These lenses can absorb uniformly across the spectrum (e.g., gray sunglasses) orselectively in certain wavelength bands (e.g., blues, so the lenses appear yellow). Absorption of blue may beadvantageous because chromatic aberration and glare can be reduced.

Advantages of absorptive lenses include:

Blocks UV which can cause cataracts and other pathologies Reduces glare Improves contrast


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May improve acuity

Figure 15. Absorptive lenses with broad and selective absorbance spectra.

Disadvantages of absorptive lenses include:

May reduce acuity Alters color values Cannot be worn at night or in dim light conditions

Hand/Stand Magnifiers

Hand magnifiers are typically positioned so that the material being viewed is at the focal point of the lens.Patients need to be made aware that the larger the lens diameter, the weaker the lens power will be.

Hand magnifiers are used with the individual's distance spectacle correction in place. They come in bothilluminated (standard or LED bulbs) and non-illuminated versions.Hand magnifier considerations include the optical design, which may be:

Spherical Aspheric/bi-aspheric, which are thinner, lighter, and flatter Aplanatic doublet


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Figure 16. Hand magnifiers.

For aspheric hand magnifiers, the front surface gradually flattens toward the edge of the lens. This designreduces or eliminates distortions induced when looking away from the optical center of the lens. Asphericlenses have directionality. This means that the more curved surface should face toward the individual using

the magnifier.

Aplanatic magnifier systems are created by using two plano-convex lenses with convex surfaces facing eachother. This results in a distortion-free image right up to the edge of the lens. Patients vary in theirappreciation of aspheric and aplanatic systems when compared to conventional spherical lenses.

Advantages of hand magnifiers include:

User can read at a more customary/longer working distance than comparable powered readingspectacles

Large range of magnifications available Low patient resistance (familiar device/cosmetically acceptable) Convenient for spot reading tasks in which information is gained from single words or short phrases

(e.g., price tags) Available with built in light source to enhance contrast Generally inexpensive, portable, and usable with the individuals spectacle correction

Disadvantages of hand magnifiers include:

Must be held with one hand (sometimes two) Prolonged reading can be slow and uncomfortable

Extended use causes hand and arm fatigue Reduced field of view slows reading Must be held at correct focal distance to obtain maximum power Less effective for individuals with limited dexterity or hand tremors Illuminated versions require batteries

Training considerations for use of hand magnifiers include:

Must establish the correct focal distance (magnifier to page distance) Must establish correct eye to magnifier distance Need to tell patients whether to use bifocal or not Need to evaluate and recommend appropriate lighting


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Stand Magnifiers are available in illuminated and non-illuminated designs. The larger the lens diameter, theweaker the lens power. Stand magnifiers need to be used with a reading correction.

Figure 17. Stand magnifiers.

Advantages of stand magnifiers include the following:

Available in very strong powers (up to 88D) Eye to lens distance can be varied Magnification is constant for a given add power Suitable with limited dexterity/hand tremors Useable at normal reading distances Useful for individuals with constricted visual fields when held at arms length Available with built in light source to enhance contrast Useable with standard reading adds Generally light weight, portable, and inexpensive

Disadvantages of stand magnifiers include the following:

Less convenient to carry due to size Requires one or both hands More bulky than hand magnifiers Awkward to use on non-flat surfaces Field of vision is smaller than equivalent powered spectacle lenses Causes excessive shading and reduces lighting onto surface (unless self-illuminated) Impossible to write under most designs Prolonged use may result in poor posture The individuals bifocal strength may not match the image plane of the stand magnifier Illuminated versions require batteries or direct current

Training considerations for stand magnifiers include:

Addressing accommodative demand of the stand magnifier (with accommodation or add) Establishing the correct working distance Evaluating and recommending appropriate lighting If stand is illuminated, patients should be taught how to change batteries and bulb

Telescopes can be hand-held or spectacle-mounted, and they can be monocular or binocular. Fixed focus,manual focus and auto focus systems are available with Galilean or Keplerian designs. They can be used for

distance, intermediate, or near vision enhancement.


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Figure 18. Telescopes.

Figure 19. Spectacle mounted bioptics.

Telescopes are afocal optical systems consisting of two lenses, separated in space by the sum of their focallengths. Galilean telescopes have a plus power objective lens and a minus power ocular lens. They form anerect/upright image. Keplerian telescopes have a plus power objective lens and a plus power ocular lens.


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Keplerian (astronomical) telescopes form an inverted image and require an erecting lens or prisms to makethem into terrestrial telescopes.

Galilean telescopes have several practical advantages for low vision work. The image is upright without theneed for erecting prisms, and the device is shorter than a Keplerian telescope. Galilean telescopes typicallyare 2, 3, or 4x in strength, inexpensive, lightweight, and have a large exit pupil, which makes centering lessdifficult.

Four power (4X) telescopes and stronger are usually Keplerian in design, which gives an optically superiorimage, but they are more expensive with a smaller exit pupil requiring better centering and aiming.Keplerian binoculars, contain prisms to erect the otherwise inverted image.

Advantages of telescopes for vision remediation:

Useful for magnification from near to distance Useful for specific tasks requiring magnification at variable distances Portable monocular units are useful for spot distance vision (e.g. signs) They can be mounted in a spectacle to leave hands free if necessary

Disadvantages of telescopes:

Field of view is restricted The higher the power of the telescope, the smaller the field of view Luminance is reduced because there is a 4% loss of light due to reflection at every lens surface. This

is reduced to some degree by the use of antireflective coatings. Depth of field is more narrowed compared to spectacle or hand-held magnifiers for near use Contrast is reduced when looking through a telescope. This can be a problem for individuals who

have experienced a reduction in their contrast sensitivity. Often relatively expensive if spectacle mounted

Training considerations for telescopes:

Need to understand focal distance limitations

Telemicroscopes (a.k.a. reading telescopes or surgical loupes) can be hand-held or spectacle mounted.Spectacle-mounted reading telescopes can be in full diameter (center-mounting) or bioptic configurations.They are available in Galilean or Keplerian designs.

Galilean telescopes used as surgical loupes require an add to be combined with the objective lens. The fieldsize is far smaller than that obtained with bifocal spectacles.

Telescopic loupes can produce asthenopia when the patient has any type of refractive error. If binocularloupes are not aligned properly, vertical or horizontal phorias can be induced.

Adopting a working distance too far inside the focal distance of the add can require excessiveaccommodation, even for a myope.

When viewing a near object through an afocal telescope, the telescope acts as a vergence multiplier. Theapproximate accommodation required is given by Aoc = M2U, where Aoc equals vergence at the eyepiecewhich also equals accommodation, U equals object vergence at the objective which equals 1/u (u is thedistance between the objective lens and the object being observed), and M equals the magnification of the

telescope.


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Advantages of telescopes include the following:

Useful for a wide range of focusing distances, from far to near Allow greater working distance than equivalently powered microscopic spectacles Spectacle-mounted design afford hands free magnification Auto focus versions available Binocularity possible for fixed focusing distances

Disadvantages of telescopes include the following:

Smaller field of view than equivalent powered microscopic spectacles Reduces image brightness Depth of focus critical requiring stability of working distance Weight Cosmesis Relatively expensive

Training considerations for telescopes include:

Establish the correct focal distance Evaluate and recommend appropriate lighting Reading material should be flat and steady due to critical depth of focus Practice required for reading due to above factors

Video Magnification Devices Closed circuit video magnification systems are available in a variety ofdifferent styles ranging from full sized systems with their own or separate monitors, to hand-held camerasystems that plug into the users own television, to portable battery powered systems.


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Figure 20. Video system used for magnification.

Figure 21. Maximum magnification obtained with a video system.


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Figure 22. Portable video display system used for reading.

Advantages of video magnification systems include:

Provide maximum contrast enhancement Allow binocularity at high levels of magnification Allow writing to be performed Provide wider field of view for an equivalent level of magnification than standard magnifiers Allow sufficient reading speed to make continuous text meaningful at high levels of magnification Level of magnification can be easily adjusted for different sizes of materials or fluctuations in vision Allow contrast to be reversed to present white letters on black background Some units allow changing the colors of letters and backgrounds Suitable for individuals with physical impairments, loss of dexterity, or hand tremors

Disadvantages of video magnification systems include:

Less portable than other devices (although portable devices are now available) More expensive than other devices Some orientation and training may be required

Training considerations for video magnification systems include:

Address accommodative demand with spectacles as needed Determine optimum magnification which will allow comfortable reading speed with maximum

reading rate

Do not under or over magnify for the task; reading versus writing tasks can require different levels ofmagnification

Instruct in proper adjustment of all controls Instruct in proper placement of reading materials Instruct in scanning to keep place while reading Practice with hand-eye coordination may be required

Head-Borne Video Magnification Devices As the name implies, these devices are worn on the patient'shead and consequently move as the head turns.

Advantages of head-borne devices include:

Provides variable levels of magnification for near, intermediate, and distance tasks


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Provides contrast enhancement Allows binocularity at high levels of magnification Allows manipulative tasks to be performed with both hands&Mac183; Level of magnification can be

easily adjusted for different sizes of materials Can provide direct input from a television

Disadvantages of head-borne devices include:

Somewhat heavy when worn for extended periods of time Requires relatively good head control (no senescent tremors) More expensive than other devices Some orientation and training may be required

Training considerations for head-borne devices:

Need to determine optimum magnification which will allow comfortable reading with maximum rate Do not under or over magnify for the task; reading versus writing may required different

magnifications Instruct in proper adjustment of all controls Instruct in proper placement of reading materials Instruct in scanning to keep place while reading Practice in hand-eye coordination may be required

Non-Optical Devices Objects used in daily living can be modified to facilitate use by low vision patients.Some modifications and special aids include:

Enlarged playing cards Enlarged bingo cards Bold rule paper Bold tipped pens Talking clocks/watches/calculator Enlarged faced thermostat dials Reading stands Level indicators Task lighting Large print reading materials Large print devices Telephones with large print buttons/displays Typoscope writing, reading, and signature template guides


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Figure 23. Typoscope reading and signature guides and other special aids for low vision patients.

Reading stands and clipboards can be helpful for maintaining proper placement of reading material. Use ofthese devices can reduce postural fatigue and facilitate placement of adequate light on reading materials.

Figure 24. Use of a lapboard and magnifier for reading.


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Figure 25. Use of a reading stand.

Use of typoscope signature and reading guides can reduce glare from glossy paper and minimize figure-ground confusion.

Some aids make use of relative size magnification, which can be used in conjunction with other forms of

magnification (i.e. use of low powered reading lenses with large print). There are a variety of optionsavailable.

Illumination is probably the single most important factor in enhancing visual functioning. The medianillumination found to give optimum performance in a low vision clinic was 1188 lux, whereas normal homeconditions have a median value of only 177 lux. More than 90% of low vision patients showed someimprovement in near or distance visual acuity when illumination was improved. (Silver JH, Gould ES, IrvineD, Cullinan TR, Visual Acuity at Home and in Eye Clinics, Trans. Ophthalmol. Soc. UK (1978) 98: 262-266)Types of illumination that can be used include:

Incandescent 60 to 75 watt bulbs in an adjustable lamp will enhance visual performance for almosteveryone who is visually impaired.

Fluorescent tubes with full spectrum outputs provide a more natural light color appearance of objects Halogen bulbs may be too bright and/or hot for many patients to use

Light fixtures are as important as the bulbs used in them. They must be flexible to allow proximity to thepaper and placement at a non-glaring angle. The position of the source must be adjustable to allowmaximum comfort/contrast enhancement. Normally, light angled in from the side of the better seeing eye is

best.


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Figure 26. Light fixture providing proper illumination.

Adaptive Technology A comprehensive review of adaptive technology is beyond the scope of this course,however a brief review of computer systems that can be beneficial for low vision patients is included as anAppendix to this course.


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Rehabilitation Instruction

Rehabilitation instruction involves the teaching of visual skills to improve overall visual functioning, bothwith and without the use of devices. Skills can include:

Eccentric viewing Scanning skills

Fixation skills Pursuits Blur interpretation Visual memory Word recognition Limitations of prescribed systems Understanding contrast and lighting Finding the proper working distance Proper use of device for all applications:

o Specific daily living skills, such as writing, sewing, self-care for diabetics, etc.

o Safety considerations such as not walking while wearing a microscope

o Organizational skillso Housekeeping issues

o Care, cleaning, battery changing, etc.

These skills can be taught by the clinician, a trained member of the staff, or a member of the low visionrehabilitation team. Some practitioners prefer to provide instruction/training on the initial visit, whereasothers prefer to schedule a separate visit.

Teaching patients about non-visual approaches to some tasks may also be helpful:

Talking books, radio reading services, descriptive video services, etc. Talking thermostats, clocks, glucometers, dictionaries, etc. Tactile substitution Braille Mobility devices

For many individuals who are visually impaired, referral to additional resources such as state blindrehabilitation agencies or Veterans Administration programs will be of value for financial assistance,vocational training, etc.It is also important to return patients to their primary (eye) care practitioner when rehabilitation iscompleted.

Report Writing

Formal communication to the referring doctor and other health care providers concerning the low visionrehabilitative care being provided is important for individuals of all ages. Communication is consistent withthe objectives of the Governments Healthy People 2010 initiative, it is a good practice builder, anddocumentation is required by most insurance plans when a consultation code is used. Consider sending areport not only to the referring doctor, but also to the patients other eye care practitioner(s), the primary care

physician, and other specialists who are involved in care of the patient.


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Low Vision Practice Management Considerations

The first thing you should know is that you already have much of the equipment you need to provide lowvision rehabilitation care in your office.Equipment typically needed for low vision care includes:

Standard exam lane Trial lenses and trial frame

Distance and near acuity charts Selected low vision devices Supplemental light sources for distance and near charts Tape measure

Staff training for low vision patient care can include:

Front office staff orientation Reading forms to patients Non-optical devices such as heavy pens, signature guides General courtesies Sighted guide technique Individuals who are visually impaired are not deaf! Have your staff observe you working with the patient

Scheduling

Most doctors allow 45-60 minutes for the initial appointment depending on what is delegated toancillary staff

Low Vision Examination refers to those portions of the exam that go beyond what one would dofor an individual that is normally sighted. These portions of the examination are generally not

covered by insurance plans and should be billed as a separate charge.

Conclusion

Currently, there are not enough optometrists providing low vision rehabilitative care to take care of thosewho are already visually impaired. As the population ages, the need for low vision rehabilitation serviceswill increase significantly. Optometry is the profession best suited to provide this care. We understandoptics, refraction, and ocular diseases. By providing low vision care, you will strengthen your connectionwith your patients and offer a unique service that will be greatly appreciated.

References

Vision Problems in the US-2002, Prevalence of Adult Vision Impairment and Age Related EyeDisease, Demographics of Visual Impairment, 4th edition, National Eye Institute, Prevent BlindnessAmerica (Source: www.usvisionproblems.org)

The Lighthouse Ophthalmology Resident Training Manual A New Look at Low Vision Care, Faye,Albert, Freed, Seidman, Fischer (2000) Lighthouse International

Low Vision Rehabilitation: Caring for the Whole Person Ophthalmology Monographs - 12, (1999),American Academy of Ophthalmology

American Academy of Ophthalmology Preferred Practice Pattern, Rehabilitation: The Managementof Adult Patients with Low Vision (1998), American Academy of Ophthalmology


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Optics, Refraction, and Contacts Lenses, Basic and Clinical Science Course, Section 3 (2004-2005),American Academy of Ophthalmology

Foundations of Low Vision, Clinical and Functional Perspectives, Corn and Koenig, (1996) AFBPress

Foundations of Rehabilitation Counseling with Persons who are Blind or Visually Impaired, Moore,

Graves & Patterson, (1997) AFB Press

Foundations of Orientation and Mobility, Second Edition, Blasch, Wiener & Welsh, (1997) AFBPress

Visual Impairments: Determining Eligibility for Social Security Benefits (2002) Board onBehavioral, Cognitive, and Sensory Sciences and Education, National Research Council, NationalAcademies Press(Source: http://www.nap.edu/books/0309083486/html/)

Clinical Low Vision, Second Edition, Faye, (1984) Little, Brown and Company

Vision and Aging, General and Clinical Perspectives, Second Edition, Rosenbloom and Morgan,(1993) Butterworth-Heinemann

The Lighthouse Handbook on Vision Impairment in Vision Rehabilitation, Silverstone, Lang,Rosenthal, Faye, (2000) Oxford University Press

Remediation and Management of Low Vision, Cole and Rosenthal, (1996) Mosby

The Art and Practice of Low Vision, Second Edition, Freeman and Jose, (1997) Butterworth-Heinemann

Appendix: Computer Software Available for Low Vision Patients

Screen Enlarging Software

Windows-based systems:

ZoomText xtra - www.aisquared.com MAGic - www.freedomscientific.com BigShot - www.aisquared.com Hal and Supernova -www.dolphincomputeraccess.com

Kurzweil 1000 - www.kurzweiledu.com

Apple Macintosh-based systems:

Zoom view (comes free on every Mac) VoiceOver -www.apple.com/macosx/features/voiceover inLarge - www.aagi.com Kurzweil 1000 - www.kurzweiledu.com Lists of other third party software can be found at www.apple.com/accessibility/vision

Screen Reading Software

Windows-based software:


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Kurzweil 1000 - www.kurzweiledu.com Window-Eyes - www.aagi.com JAWS for Windows -www.freedomscientific.com ZoomText xtra - www.aisquared.com Hal and Supernova -www.dolphincomputeraccess.com Outspoken - www.aagi.com

Apple Macintosh-based software:

Outspoken - www.aagi.com VoiceOver -www.apple.com/macosx/features/voiceover Kurzweil 1000 - www.kurzweiledu.com Speech Recognition Talking Alerts software from www.apple.com/accessibility/physical

Operating System Software

Windows-based:

Magnifier magnifier utility (2-9X) Narrator text to speech utility Options for users with visual impairments

-www.microsoft.com/resources/documentation/Windows/2000/server/reskit/en-us/deploy/dghe_acc_qqfa.asp

Apple Macintosh-based:

Zoom View (free on every Mac) in

Documents

Review of Low Vision Rehabilitation