CHAPTER II

LITERATUR RIVIEW

A. Optic Nuritis

A.1 Definition

Optic neuritis, or primary inflammation of the optic nerve, is referred to as

papillitis when the optic disc is swollen and retrobulbar neuritis when the disc appears

normal (Yanoof, 2008). The etiology of optic neuritis can be secondary to

demyelination, vasculitis (such as secondary to systemic lupus erythematosus),

infection (such as syphilis or post-viral optic neuritis, most commonly seen in children)

or a granulomatous process (such as Wegener's granulomatosis or sarcoidosis).

Demyelination may be isolated or associated with multiple sclerosis (MS) (Thurtell,

2012).

A.2 Epidemiology and Pathogenesis

The annual incidence of optic neuritis, as estimated in population-based studies,

is approximately 3–5 per 100,000 per year, while the prevalence is 115 per 100,000.

The majority of patients who develop optic neuritis are between the ages of 20 and 50

years. Women are affected more commonly than men. In the ONTT, 77% of the

patients were women, 85% were white, and the mean age was 32 ± 7 years. In most

cases, the pathogenesis of optic neuritis is inflammatory demyelination, whether or not

MS is diagnosed clinically. It is likely that many cases of monosymptomatic optic

neuritis occur as the initial manifestation of MS (Yanoof, 2008)

A.3 Ocular Manifestations

Loss of vision in patients with acute demyelinating optic neuritis is usually

abrupt and occurs over several hours to days. Progression for more than one week or

failure of recovery to begin within four weeks is possible but suggests an alternative

underlying cause. Visual loss is usually monocular, although occasionally both eyes

are affected simultaneously, particularly in children (Yanoof, 2008).

There are features of typical demyelinating ON in adults (Shams and Plants,

2009):

1. Acute to subacute onset – progressive over a few days to 2 weeks

2. Young adult patient, typically less than 45 years of age, but may be of any age

3. Periocular pain (90%), especially with eye movement – preceding or coinciding

with visual loss

4. Unilateral loss of visual acuity – variable severity

5. Reduced contrast and colour vision – out of proportion to loss of visual acuity

6. Exacerbation of symptoms with increased body temperature (Uhthoff’s

phenomenon)

7. Ipsilateral relative afferent pupillary defect

8. Normal (65%) or swollen (35%) optic nerve head

9. Mild periphlebitis (venous sheathing)

10. Visual field defect – almost any type

11. Spontaneous visual improvement in >90% starting within 2–3 weeks regardless of

treatment

12. No deterioration in vision when corticosteroids are withdrawn

13. Pallor of the optic disc is seen within 4–6 weeks from onset of visual loss

14. Overall, 50% of clinically isolated cases of ON go on to develop a second MS-

defining episode by 15 years. The risk of developing MS is 25% when baseline

MRI is normal and 75% when MRI has one or more brain lesions typical for MS.

15. Ancillary investigations suggestive of MS

Mild pain in or around the eye is present in more than 90% of patients. Such

pain may precede or occur concomitantly with visual loss, is usually exacerbated by

eye movement, and generally lasts no more than a few days. The presence of pain,

particularly on eye movement, is a helpful (although not definitive) clinical feature that

differentiates acute demyelinating optic neuritis from nonarteritic anterior ischemic

optic neuropathy (AION) (Yanoof, 2008).

On examination of the patient, optic nerve dysfunction is evident. The severity

of visual loss varies from a mild visual field defect to severe loss of central acuity (3%

of ONTT participants had no light perception, and 90% described at least some loss of

central acuity). Severe loss of visual acuity is more common in children. Color vision

and contrast sensitivity are impaired in almost all cases, often out of proportion to

visual acuity. Visual field loss, which may be diffuse (48%) or focal (i.e. nerve fiber

bundle defects, central or cecocentral scotomas, hemianopic defects), is also common

in acute optic neuritis. Altitudinal defects (focal visual field loss above or below the

horizontal meridian) are less common and should prompt consideration of a diagnosis

of anterior ischemic optic neuropathy (AION). Low-contrast letter acuity has recently

emerged as a very sensitive test for optic neuropathy. An afferent pupillary defect

(APD) is detected in almost all unilateral cases of optic neuritis. If an APD is not

present, a pre-existing optic neuropathy in the fellow eye must be suspected. In fact,

asymptomatic visual dysfunction is fairly common among fellow eyes of patients who

have apparent unilateral optic neuritis.

The optic disc appears normal in approximately two thirds of adults with acute

demyelinating optic neuritis (retrobulbar optic neuritis), while disc swelling is present

in about one third of adult cases (papillitis) ( Fig.1 ); children with optic neuritis

experience optic disc swelling more frequently than do adults.[29] Funduscopic features

of optic disc swelling include elevation of the optic nerve head, disk hyperemia,

blurring of the disc margins, and edema of the nerve fiber layer.[31] Although the

clinical features are similar in both forms, optic disc hemorrhages were uncommon in

the ONTT (6%), and their presence should suggest an alternative diagnosis.

Fig. 1 Optic disc swelling (papillitis) associated with acute optic neuritis

A.4 Diagnosis

The diagnosis of acute demyelinating optic neuritis is based on an appropriate

history (typical versus atypical course) and clinical signs and symptoms as described

above. Diagnostic tests, including magnetic resonance imaging (MRI), cerebrospinal

fluid (CSF) analysis, and serological studies, usually are performed for the following

reasons:

1. To determine if the cause is noninflammatory (such as a compressive lesion), or a

nonidiopathic inflammatory or infectious process in cases that are not typical for

acute demyelinating optic neuritis.

2. To determine the prognosis or risk for subsequent development of MS in

monosymptomatic cases for which the history and clinical signs are typical

In patients with suspected optic neuritis, MRI of the brain and orbits with fat

suppression and gadolinium should be performed, even in typical cases, to confirm the

diagnosis and to assess for the presence of other white matter lesions. Optical

coherence tomography (OCT) may be useful in predicting the subset of optic neuritis

patients who will suffer persistent visual dysfunction; a 2006 study of 54 patients

documented a poor visual outcome in patients with a retinal nerve fiber layer (RNFL)

thickness of less than 75μm measured with OCT within 3–6months of an initial optic

neuritis event (Yanoof, 2008).

A.5 Differential Diagnosis

The diagnosis of acute visual loss begins with the localization of the involved

portion of the visual system. An optic neuropathy is presumed when no ocular cause

for visual loss is apparent and an APD is present. Because most cases of optic neuritis

produce unilateral visual loss, discussion here is limited to unilateral optic

neuropathies. When there is acute visual loss and unilateral optic disc swelling, both

optic neuritis and AION must be considered. Although the clinical profiles of these

disorders overlap, AION is typically painless, occurs in patients over 50 years of age,

and may be associated with optic disc hemorrhages. When the optic disc is normal in

patients with unilateral optic neuropathy, a compressive lesion must be excluded; this

usually is differentiated from acute optic neuritis by a history of progressive visual loss

beyond the typical period of 1–2 weeks.

A.6 Pathology

Although the exact underlying cause is unknown, the pathophysiology of acute

optic neuritis and MS is that of primary inflammatory demyelination. Very little is

written about the pathology of “isolated” optic neuritis, and no autopsy data have been

reported. The inflammatory response in MS plaques is marked by perivascular cuffing,

T cells, and plasma cells. Although MS, itself, previously was thought to be

exclusively a disease of myelin with sparing of nerve axons, neuronal and axonal loss

have been demonstrated to occur pathologically.

A.7 Treatment

Major findings of the ONTT with regard to treatment of acute optic neuritis may

be summarized as follows: (1) intravenous methylprednisolone treatment hastens

recovery of visual function but does not affect long-term visual outcome; this benefit

was greatest in the first 15 days; (2) patients treated with oral prednisone alone

(without intravenous methylprednisolone) unexpectedly demonstrated an increased

risk of recurrent optic neuritis (30% after 2years versus 16% for the placebo group and

13% for those receiving intravenous steroids) that has persisted throughout the 10+-

year follow-up period (44% after 10 years versus 31% for the placebo group and 29%

for those receiving intravenous steroids); and (3) monosymptomatic patients in the

intravenous methylprednisolone group had a reduced rate of development of MS

during the first 2 years of follow-up, but this benefit did not persist beyond 2years and

was seen only in patients with brain MRI scans that indicated a high risk for

subsequent MS (originally described as MRI scans with two or more white matter

lesions, 10-year follow-up data has confirmed one or more white matter lesions as an

equivalent risk) (Yanoof, 2008).

In patients with a typical clinical course and examination findings for acute

monosymptomatic demyelinating optic neuritis (first demyelinating event), MRI of the

brain should be performed to determine whether they are at high risk for the

development of MS. Characteristic demyelinating lesions in patients at risk for

multiple sclerosis are 3 mm or larger in diameter, are ovoid, are located in

periventricular areas of the white matter, and radiate toward the ventricular spaces.

Oligoclonal banding of proteins in the cerebrospinal fluid is a useful predictor of the

risk of multiple sclerosis among patients with either normal brain MRI or abnormal

findings that are not classic for demyelination (e.g., small, punctate lesions that are not

periventricular or ovoid).

The presence of two or more white matter lesions on MRI (3mm diameter or

larger, at least one lesion periventricular or ovoid) should prompt consideration of one

of the following treatments:

•    Intravenous methylprednisolone (1g per day, single or divided doses, for 3 days) followed by oral prednisone (1mg/kg per day for 11 days, then 4-day taper).

•    Interferonβ-1a (Avonex 30μg intramuscularly once a week).

•    Interferonβ-1a (Rebif 22μg subcutaneously once a week).

•    Betaseron (250μg subcutaneously every other day).

In monosymptomatic patients who have fewer than two MRI white matter

lesions, and in those for whom a diagnosis of MS has been established, intravenous

methylprednisolone treatment (followed by oral prednisone as outlined) may be

considered on an individual basis to hasten visual recovery, but this has not been

demonstrated to improve long-term visual outcome. Effects of corticosteroid treatment

and other therapies on the recovery of visual function and on the risk of multiple

sclerosis in children have not been established by randomized trials, but intravenous

methylprednisolone treatment is generally recommended if visual loss is unilateral and

severe or is bilateral.

Based on findings from the ONTT, oral prednisone alone (without prior

treatment with intravenous methylprednisolone) may increase the risk of recurrent

optic neuritis and should be avoided. A short course of nonsteroidal anti-inflammatory

agents may be helpful in the occasional case of disabling pain associated with optic

neuritis (Yanoof, 2008)

B. Cataract

B.1 Definition

A cataract is any opacity in the lens. Aging is the most common cause of

cataract, but many other factors can be involved, including trauma, toxins, systemic

disease (such as diabetes), smoking, and heredity. Age-related cataract is a common

cause of visual impairment (Vaughan and Asburys, 2007).

B.2 Pathogenesis

The pathogenesis of cataracts is not completely understood. However,

cataractous lenses are characterized by protein aggregates that scatter light rays and

reduce transparency. Other protein alterations result in yellow or brown discoloration.

Additional findings may include vesicles between lens fibers or migration and aberrant

enlargement of epithelial cells. Factors thought to contribute to cataract formation

include oxidative damage (from free radical reactions), ultraviolet light damage, and

malnutrition. No medical treatment has been found that will retard or reverse the

underlying chemical changes that occur in cataract formation. However, some recent

evidence suggests a protective effect from dietary carotenoids (lutein), but studies

evaluating the protective effect of multivitamins have yielded conflicting results

(Vaughan and Asburys, 2007).

B.3 Classification

Table 1. Classification of cataracts according to maturityNo Cataract form Visual acuity1 Developing cataract Still full (0.8–1.0)2 Immature cataract Reduced (0.4–0.5)3 Developed cataract Severely reduced (1/50–0.14 Mature cataract

Hypermature cataractLight and dark perception, perception of hand ovements in front of the eye

Table 2. Form senile catarac

B.4 Clinical Manifestation

1. History

Careful history taking is essential in determining the progression and

functional impairment in vision resulting from the cataract and in identifying other

possible causes for the lens opacity. A patient with senile cataract often presents

with a history of gradual progressive deterioration and disturbance in vision. Such

visual aberrations are varied depending on the type of cataract present in the patient.

a) Decreased visual acuity 

Decreased visual acuity is the most common complaint of patients with

senile cataract. The cataract is considered clinically relevant if visual acuity is

affected significantly. Furthermore, different types of cataracts produce different

effects on visual acuity.

For example, a mild degree of posterior subcapsular cataract can produce

a severe reduction in visual acuity with near acuity affected more than distance

vision, presumably as a result of accommodative miosis. However, nuclear

sclerotic cataracts often are associated with decreased distance acuity and good

near vision.

A cortical cataract generally is not clinically relevant until late in its

progression when cortical spokes compromise the visual axis. However,

instances exist when a solitary cortical spoke occasionally results in significant

involvement of the visual axis.

b) Glare

Increased glare is another common complaint of patients with senile

cataracts. This complaint may include an entire spectrum from a decrease in

contrast sensitivity in brightly lit environments or disabling glare during the day

to glare with oncoming headlights at night. Such visual disturbances are

prominent particularly with posterior subcapsular cataracts and, to a lesser

degree, with cortical cataracts. It is associated less frequently with nuclear

sclerosis. Many patients may tolerate moderate levels of glare without much

difficulty, and, as such, glare by itself does not require surgical management.

c) Myopic shift

The progression of cataracts may frequently increase the diopteric power

of the lens resulting in a mild-to-moderate degree of myopia or myopic shift.

Consequently, presbyopic patients report an increase in their near vision and less

need for reading glasses as they experience the so-called second sight. However,

such occurrence is temporary, and, as the optical quality of the lens deteriorates,

the second sight is eventually lost.

Typically, myopic shift and second sight are not seen in cortical and

posterior subcapsular cataracts. Furthermore, asymmetric development of the

lens-induced myopia may result in significant symptomatic anisometropia that

may require surgical management.

d) Monocular diplopia

At times, the nuclear changes are concentrated in the inner layers of the

lens, resulting in a refractile area in the center of the lens, which often is seen

best within the red reflex by retinoscopy or direct ophthalmoscopy.

Such a phenomenon may lead to monocular diplopia that is not corrected

with spectacles, prisms, or contact lenses.

2. Physical

After a thorough history is taken, careful physical examination must be

performed. The entire body habitus is checked for abnormalities that may point out

systemic illnesses that affect the eye and cataract development.

A complete ocular examination must be performed beginning with visual

acuity for both near and far distances. When the patient complains of glare, visual

acuity should be tested in a brightly lit room. Contrast sensitivity also must be

checked, especially if the history points to a possible problem. Examination of the

ocular adnexa and intraocular structures may provide clues to the patient's disease

and eventual visual prognosis.  

A very important test is the swinging flashlight test which detects for a Marcus

Gunn pupil or a relative afferent pupillary defect (RAPD) indicative of optic nerve

lesions or diffuse macular involvement. A patient with RAPD and a cataract is

expected to have a very guarded visual prognosis after cataract extraction.

A patient with long-standing ptosis since childhood may have occlusion

amblyopia, which may account more for the decreased visual acuity rather than the

cataract. Similarly, checking for problems in ocular motility at all directions of gaze

is important to rule out any other causes for the patient's visual symptoms.

Slit lamp examination should not only concentrate on evaluating the lens

opacity but the other ocular structures as well (eg, conjunctiva, cornea, iris, anterior

chamber).  

1) Corneal thickness and the presence of corneal opacities, such as corneal guttata,

must be checked carefully.

2) Appearance of the lens must be noted meticulously before and after pupillary

dilation.

3) The visual significance of oil droplet nuclear cataracts and small posterior

subcapsular cataracts is evaluated best with a normal-sized pupil to determine if

the visual axis is obscured. However, exfoliation syndrome is appreciated with

the pupil dilated, revealing exfoliative material on the anterior lens capsule.

4) After dilation, nuclear size and brunescence as indicators of cataract density can

be determined prior to phacoemulsification surgery. The lens position and

integrity of the zonular fibers also should be checked because lens subluxation

may indicate previous eye trauma, metabolic disorders, or hypermature

cataracts.

The importance of direct and indirect ophthalmoscopy in evaluating the

integrity of the posterior pole must be underscored. Optic nerve and retinal

problems may account for the visual disturbance experienced by the patient.

Furthermore, the prognosis after lens extraction is affected significantly by

detection of pathologies in the posterior pole preoperatively (eg, macular edema,

age-related macular degeneration).

B.5 Treatment

Care of the patient with cataract may require referral for consultation with or

treatment by another optometrist or an ophthalmologist experienced in the treatment of

cataract, for services outside the optometrist's scope of practice. The optometrist may

participate in the comanagement of the patient, including both preoperative and

postoperative care. The extent to which an optometrist can provide postoperative

treatment for patients who have undergone cataract surgery may vary, depending on

the state's scope of practice laws and regulations and the individual optometrist's

certification. presents a flowchart for the optometric management of the adult patient

with cataract.

Under most circumstances, the standard of care in cataract surgery is removal of

the cataract by extracapsular cataract extraction (ECCE), using either

phacoemulsification (PE) or nuclear expression. ECCE has replaced intracapsular

cataract extraction (ICCE) as the standard of care for primary cataract extraction

although ICCE is still used under certain special circumstances.65 The following brief

descriptions show the nature as well as special indications and risks of each surgical

procedure.

1. Extracapsular cataract extraction by phacoemulsification.

After the opening incision and anterior capsulotomy, an ultrasonic probe emulsifies

the hard nucleus, enabling the surgeon to remove the lens material using a suction

device. This procedure maintains the normal depth of the anterior chamber. The

wound is then enlarged to allow insertion of a posterior chamber IOL into the

capsular bag. Depending on the configuration of the wound, the incision may be

closed with a single suture or without sutures.

2. Extracapsular cataract extraction by nuclear expression.

Following the opening incision and anterior capsulotomy, the nucleus is expressed

from the capsular bag and removed in one piece through the incision. The residual

cortex is removed by irrigation and aspiration. This procedure requires a larger

incision, usually necessitating several sutures to close the wound.

3. Intracapsular cataract extraction. Following the opening

incision, the entire lens is extracted in one piece, with the nucleus and cortex still

enclosed in the lens capsule. Because this procedure requires a very large incision

and carries a much higher risk of loss of vitreous and postoperative complications,

it is seldom performed. However, it may be preferable to remove the cataract by

this procedure in special circumstances (e.g., damaged zonules secondary to

trauma).