Presbyopia
Presbyopia: presby (old) + opia
(vision)
Presbyopia is a term we use to describe the condition in which a patient's
amplitude of accommodation has decreased to the point where clear or
comfortable vision at the desired nearpoint is not obtainable.
The amplitude of accommodation gradually decreases with age (remember
Donder's Formula). Presbyopia generally occurs when the patient's
amplitude of accommodation is less than 5 D. At this point the patient is
required to use more than half their amplitude of accommodation at the
near point. This is the point where most patients become symptomatic. The
age of onset of presbyopia is variable, but note in
the following tables (from Duane) that the majority of patients will need
near correction by age 45.
Amplitude of Accommodation
- Maximum Amplitude= 25-0.4(age)
- Probable Amplitude= 18.5-.3(age)
- Minimum Amplitude= 15-0.25(age)
| Age |
AMP of ACCOM |
AGE |
AMP of ACCOM |
| 10 |
11.00 |
35 |
6.5 |
| 15 |
10.25 |
40 |
5.50 |
| 20 |
9.50 |
45 |
3.5 |
| 25 |
8.50 |
60 |
1.25 |
| 30 |
7.50 |
70 |
1.00 |
|
| Age |
Amplitude less than 5 D |
| |
Myopes |
Hyperopes |
| 38 |
0% |
17% |
| 40 |
23% |
67% |
| 42 |
57% |
70% |
| 44 |
75% |
92% |
| 45 |
82% |
100% |
|
You will note from the above table that hyperopes become presbyopic
earlier than myopes.
Symptoms
- Vision at the patient's normal near point becomes blurred
- Symptoms of uncorrected hyperopia appear
- "Pulling" or eyestrain with reading
- Complaints of fatigue with reading
Many factors in addition to distance refractive error and amplitude of
accommodation will determine when your patient requires a correction for
presbyopia. Some of these factors include:
- Occupation
- Pupil Size (depth of field)
- Reading Habits, Hobbies, other near vision demands
- Stature (long arms help delay the need for correction)
Westheimer (1953) compiled the following data for depth of field in
diopters for different pupils sizes (20/20 Acuity)S equals
spectacle correction minus the accommodation in use:
| Pupil Size |
| S |
2 mm |
4 mm |
6 mm |
| -10 |
.840 |
.425 |
.290 |
| -8 |
.820 |
.410 |
.280 |
| -6 |
.800 |
.400 |
.270 |
| -4 |
.775 |
.390 |
.260 |
| -2 |
.760 |
.380 |
.255 |
| 0 |
.750 |
.375 |
.250 |
| +2 |
.740 |
.370 |
.245 |
| +4 |
.730 |
.370 |
.245 |
| +6 |
.720 |
.365 |
.240 |
| +8 |
.710 |
.360 |
.235 |
| +10 |
.690 |
.360 |
.230 |
Signs
- Decreased Amplitude of Accommodation
Correction of Presbyopia
The correction of presbyopia requires the application of plus lenses in
addition to the refractive correction at distance, determined as
the lens power which yields clear and comfortable vision at the near
point.
Determination of Add Power
- By Amplitude of Accommodation
- The principle with this procedure is to permit the patient to use one
half to two thirds of their total amplitude of accommodation:
Add Power= 1/working distance (meters)-1/2(amplitude of accommodation)
- By Range of Accommodation
- This procedure uses the range of accommodation measured in the tests
of relative accommodation (NRA & PRA).
- The difference between the NRA and 1/2 the accommodative range equals
the add power
- Example
- PRA -0.50
- NRA +2.00
- Range 2.50
- +2.00 - (2.50/2) = +.75
- BCC Method
- With this method the value determined for the BCC testing is used as
the tentative add power
- Plus Build Up
- Add plus lens power +0.25D at a time until patient can comfortably
read near chart
- AGE
- There are many age tables available for guess-timating the add power
required. One problem with this approach is that it assumes that all
individuals of the same age have the same amplitude of accommodation,
which is not the case in practice
- A simple formula for predicting the add power given the age is: +0.75D
at age 40 + 0.1D(age-40)
Changes in Near Test Results in Presbyopia
- Decreased Amplitude of Accommodation
- Increased BCC
- Decreased PRA (minus lens to blur)
- Increase in exophoria/ decrease in esophoria due to a decrease in
accommodative convergence
- Increase in near point BI blur, break, recovery
- Decrease in near point base out blur, break, recovery
- Absence of Blur finding with BO Prism (Positive Vergences)
Exophoria in Presbyopia
A high near point exophoria is often associated with presbyopic adds. This
generally does not produce symptoms of diplopia or asthenopia. Presbyopes
with high exophoria at near are usually less symptomatic than
nonpresbyopes with the same degree of exophoria.