Upload
gauri-shankar-shrestha
View
309
Download
3
Tags:
Embed Size (px)
DESCRIPTION
Citation preview
Gauri S. Shrestha, M.Optom, FIACLECo-Ordinator
B.Optom ProgramInstitute of Medicine
Dipak Sah, B.optom final Year
Accommodation Age normal amplitude of accommodation Range of Accommodation Near vision
Gradual decrease in amplitude of accommodation as expected with age
The onset is usually anticipated by age 40 years or amplitude of accommodation tends to drop below 5.00D.
Old aged eye ( आँ�खा� बु�ढो� भयो�)
Age Functional effect
Hyperopia Additional accommodative demand
Occupation Near vision demands
Gender Earlier onset in females (short stature, menopause)
Systemic disease Diabetes mellitus, multiple sclerosis, cardiovascular accident
Drugs alcohol, chlorpromazine, hydrochlorothiazide, antianxiety agents, antidepressants
Geographic factors
Proximity to the equator (higher average annual temperatures, greater exposure to ultraviolet radiation)
Iatrogenic factors laser photocoagulation; intraocular surgery
Incipient presbyopia Premature presbyopia Manifest presbyopia Absolute presbyopia
Incipient presbyopia◦Beginning stage of presbyopia when symptoms or difficulty are first encountered in near vision.
◦Patient will have more difficulty in dim illumination while can do well in bright illumination.
Premature presbyopia◦Presbyopia occuring at an earlier age than expected for normal population.
◦Usually associated with ocular diseases, nutritional deficiencies or ingestion of certain drugs.
Manifest presbyopia◦Presbyopia with some amplitude of accommodation present.
Absolute presbyopia◦Presbyopia with amplitude of accommodation completely absent.
“My arms are not long enough to see up close anymore”
Blurring of near vision Drowsiness after a short period of near work. Headache
Biomechanical Biochemical Physiological
Decrease in elasticity of lens material (44%)
Decreased elasticity of capsule Increase in size of lens Anterior shifting of the equatorial fibers
Increased disulphide bondings between the lens material and the capsule.
Increase in size Alteration of the lens material (Not any sclerosis)
HYPEROPES
EMMETROPES
MYOPES
Half in reserve for distance greater than 40 cm
One third in reserve for working distance less than 40 cm
Addition based on amplitude of accommodation.
Tentative addition based on age. Plus build-up method. Bichrome method. Cross-cylinder method. Relative accommodation method. Dynamic Retinoscopy method.
Amplitude of accommodation decreases with age..◦Presbyopia is reported when NPA exceeds 8 inches
(22cm) ie AA = 4.50D (Donders)
Presbyopia exists when amplitude of accommodation is less than 5D (Morgan).
Working distance (WD)= 40cmRAF (Amp accommodation) = 2.00D
What should be the near addition ???Accommodation required for WD = 2.50 DAccommodation in Reserve = 1.00DAmount of accommodation left = 1.00DAmount of Near addition = (2.50 –1.00)
= 1.50D
Example 2
Working distance (WD) = 25 cmRAF (Amp accommodation) = 1.50D
What should be the near addition ??? Accommodation needed at WD = 4.00DAmplitude held in reserve = 0.50DAmplitude of accommodation left =
1.00DAmount of near addition = (4.00-1.00)
= 3.00D
Amplitude of accommodation to age (Hofstetter)◦Maximum = 25.0 – 0.4 (age)◦Probable = 18.5 – 0.3 (age)◦Minimum = 15.0 – 0.25 (age)
◦Amount of near add calculated by holding certain amount of accommodation in reserve
Rule of 4s ( ४ को� नि�योम)= 4*4-age/4
Age of Range (Years)
Minimum Expected Amplitude (Diopter)
Range of Near Add in Diopter for 40 cm.
40 to 44 5.00 to 4.00 +0.75 to +1.00
45 to 49 3.75 to 2.75 +1.00 to +1.50
50 to 54 2.50 to 1.50 +1.50 to +2.00
55 to 59 1.25 to 0.25 +2.00 to +2.25
60 and over 0 +2.25 to +2.50
Can be done binocularly or monocularly Plus lenses are increased in steps of 0.25D to the
amount necessary to read the desired letters at a customary working distance.
Monocular build-up usually lands in more amount of near addition.
Chromatic aberration In presbyopic patients red
& green are focused behind the retina with red farther away.
Green appears clear. Plus lenses are added until
both red & green appear equally clear
Can be combined this technique with tentative add method/amplitude method etc
Bichromatic method:◦Patient with Rx for DV, ◦Bichrome test at habitual distance in
NV◦Ask patient which background
letters are more clear Green-add plus, Red-remove plus until he/she sees letters equally
clear in both
A near point grid is presented to the patient at their customary working distance.
Illumination on the target should be diffuse.
Plus lenses are added until patient sees the lines clearly
Crossed cylinder (±0.50D) with their minus axes vertical are placed before the patient’s eyes.
Patient is asked to report which sets of lines running across or up & down appear clearer, sharper, blacker
Cross cylinder creates artificial astigmatism with an interval of sturm of 1D
If patient accommodates exactly for the target, both sets of lines should be equally clear.
If patient under-accommodates, the horizontal lines will appear clear.
Add positive lenses until verticle and horizontal lines are seen equally clearly◦Can be done monocularly or binocularly
Measure of lenses to blur letters of N6. Patient is provided with plus lenses determined by
bichrome method/add based on age/Amplitude method
Determine◦Minus lens to blur (PRA)◦Plus lens to blur (NRA)
Near add = NRA+PRA/2
The addition is 1.00 (say) We add minus lenses until blur and the value be (1-
0.5)= +0.50 D We add plus lenses and the value be +2.00 D= (1+1) Then the final add is (+0.50+2.0)/2=
1.25D
Determine lag of accommodation (dynamic retinoscopy)
Reduce amount of lag by +0.50 to +0.75D
Prescribe remaining as addition for near
Method Procedure Advantage
40 cm fused (binocular) cross-cylinder.
Compare manifest refraction to plus value on 40 cm fused cross-cylinder, add is the plus over the manifest refraction.
In older patient with limited accommodative amplitude and accommodative flexibility.
One-half accommodative amplitude
Accommodative amplitude determined from PRA, add based on allowing the patient to use only one-half of available amplitude at the desired reading distance.
Good for early presbyopia with slightly reduced amplitude of accommodation account for the patient’s desired reading distance.
PRA/NRA Plus add is the value that puts the total near power in the middle of the PRA/NRA blur points.
Add is the middle of the Accommodative range from PRA to NRA
Plus lens(Convex
lens)
Thank YOU