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advantage of allowing the examiner to read directly the distance from the subject’s eyes to the chart.
Table 11-4 shows the approximate relationship between age and accommodative power.
11.3.55 Presbyopia occurs in all eyes although there is considerable variation between individuals. For
most emmetropic individuals reading becomes a little difficult in the middle to late forties. In uncorrected
hyperopes the problem will occur at an earlier age because some of the eye’s accommodative power must be
used to overcome the hyperopia. Myopes, on the other hand, can simply remove their distance spectacles
when presbyopia becomes significant, and many individuals with 3 or 4 dioptres of myopia never need any
reading spectacles.
11.3.56 It is not acceptable for myopic flight personnel who are also presbyopic to simply remove their
distance spectacles in order to read. Such individuals must have a spectacle correction which is satisfactory for
both distance and near, that is to say, some type of multifocal correction.
11.3.57 The symptoms of presbyopia depend mainly on the amount of accommodation available but also
to a considerable extent on illumination level, clarity and contrast of the print, pupil size, degree of fatigue, and
general well-being of the subject. Most normal subjects are comfortable using up to half their accommodative
amplitude. Figure 11-7 shows maximum and effective or comfortable amplitude of accommodation.
Figure 11-8 shows how the amplitudes are affected by pre-existing refractive errors. When prescribing reading
spectacles or a bifocal addition to distance spectacles one generally tries to leave about half the
accommodative amplitude in reserve.
11.3.58 The increasing density of the lens, which is the basis of presbyopia, also results in generalized
reduction of the brightness of the retinal image. This, together with the smaller pupils and steady loss of
photoreceptors, explains why older persons generally need more light than younger persons for a given visual
task.
Table 11-4. Age and presbyopia
Age Dioptres Near-point (cm)
15 12 8
25 10 10
35 7 14
45 4 25
55 1.5 67
65 1.1 91
III-11-18 Manual of Civil Aviation Medicine
Figure 11-7. Maximum and effective accommodation range
Impaired accommodation
11.3.59 Diminished accommodation with the associated impairment of near vision can be caused by the
following:
a) Poor general health
b) Severe mental stress
c) Hypoxia
d) High G-forces
e) Cycloplegic drops
16 20 24 28 32 36 40 44 48 52 56 60
Years of age
2
4
6
8
10
12 8.3
10.0
12.5
16.7
25.0
50.00
1.0
Nearpoint
(cm)
Range of
accommodation
(Dioptres)
Maximum
Effective
Part III. Medical Assessment
Chapter 11. Ophthalmology III-11-19
Figure 11-8. Change of accommodation range by pre-existing ametropia
f) Ganglion blocking agents
g) Atropine-like drugs
h) Mood altering drugs and tranquilizers
i) Disorders affecting the IIIrd cranial nerve
j) Iritis and other disorders of the ciliary muscle.
Eye strain (asthenopia)
11.3.60 Complaints of eye strain are very common and include blurring of vision, print running together,
heavy or tired feeling of the eyes, burning sensation of the eyes, headaches, ocular pain, tearing, redness of
the eyes, need to rub the eyes, increased light sensitivity and inability to do close work for any length of time.
16 20 24 28 32 36 40 44 48 52
Years of age
2
4
6
8
10
12 8.3
10.0
12.5
16.7
25.0
50.00
Nearpoint
(cm)
Dioptres
Myopia
1 dioptre
Hypermetropia
1 dioptre
III-11-20 Manual of Civil Aviation Medicine
11.3.61 Frequently, patients complaining of eye strain have completely normal ocular examinations and
the cause of the symptoms may be general fatigue, stress or some systemic disease. Sometimes there are
important ocular disorders needing treatment. These include blepharitis, conjunctivitis, dry eye syndromes,
uncorrected refractive errors, including presbyopia, convergence insufficiency and other ocular muscle
imbalance problems.
Methods of assessing near visual acuity
11.3.62 The wide variety of different test types used by Contracting States has made standardization of
near vision testing difficult. For many years the Jaeger test types were in common use. The standard now
adopted in Annex 1 is the font called “Times Roman”. The size of the letters is based on the old printer’s system
in which one point is 0.35 mm (1/72 in). Thus 5-point type is one in which each letter is cast on a block 1.75 mm
　
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