Presbyopia is an age-related progressive loss of the focusing power of the lens. This results in difficulty in reading and seeing near objects.
- Causes, incidents, and risk factors:
- The focusing power of the eye, which depends upon the inherent elasticity of the lens, gradually decreases in old age.
- This causes the inability to read at normal reading distance (33 cm to 40cm).
- People usually notice the condition around age 40; after they realise that they need to hold reading materials further away in order to focus.
- Signs and tests
A general eye examination will be performed including measurements to determine a prescription for glasses or contact lenses.
Tests may include:-
- Visual acuity
- Refraction
- Muscle integrity
- Slit lamp
- Retinal examination
- Symptoms
- Inability to focus near objects
- Likes to read in brilliant illumination when the pupil will be forced to constrict
- Eyestrain
- Headache
- Factors affecting close work
1. Pupil size- Smaller pupils increase the pinhole effect, which increases the depth of focus
2. Lighting - Small print is easier to read in bright light. The contrast is improved and the reflected light may constrict the pupil, improving the depth of field
3. Print size and print distance -large print is easier to read
4. Task requirements - An accountant will need better near vision than a garbage worker
5. Secondary task considerations- A Secondary task considerations person wants to increase the near working distance in one pair of glasses rather than buy two pairs of glasses
6. Body type and position - Body type and position some people, particularly those with long arms, like to hold reading materials further away than others do. In this case the add power will be less
7. Previous correction - Many people don’t tolerate an increase in add power greater than 0.75D at any one time
8. Low ametropia - Uncorrected low hypermetropes complain of reading difficulty at an earlier age than uncorrected low myopes.
9. Health and medications: Diabetics typically need near correction at an earlier age and need stronger add power than is normal for their age group.
Age Expected add power
38 yrs + 0.75 DS
40 yrs +1.0 DS
45 yrs + 1.50 DS
50 yrs + 2.0 DS
55 yrs +2.5 DS
60 yrs and above +3.0 DS
Variations of accommodation with age
- Amplitude of Age Accommodation
Early Age --- 14 D, Near point - 7 cm
36 Yrs -- 7 D, Near point - 14 cm
45 yrs -- 4 D, Near point - 25m
60 yrs -- 1D, Near point - 1m
Evaluation of presbyopia
- Treatment
Presbyopia can be corrected with appropriate lenses, so that his accommodation is reinforced and the near point is brought within the useful working distance.
- Know the working distance of the patient for proper addition
- Refraction
- Determine the amplitude of accommodation
- Supplement this by the lens
- allowing him a sufficient reserve of accommodation
- Key points to remember
- Presbyopic spectacle should never be prescribed mechanically based on age
- Lenses must be comfortable - Vision for the particular work for which their spectacle is intended must be kept in mind.
- Start with addition of +0.75D - Better to under correct than over correct
- Lenses that bring the near point closer than 28cm are rarely tolerated.
- Demand for higher correction than convergence should be added with base in prism
- Patient with early cataract can read with +3.50 D or + 4.0D addition
- Usual discomfort for presbyopic optical correction is due to over-correction
- Types of corrective spectacle for presbyopia:
1. Single vision reading glasses
2. Bifocals - where glasses are given for near and distance
3. Trifocals - where glasses are given for distance, intermediate and near vision
4. Varifocals - progressive addition lens
5. Monovision correction- one eye is corrected for distance and the other eye for near
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