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OPHTHALMOLOGY
11.1 INTRODUCTION
11.1.1 This chapter outlines the principles of ophthalmologic examination and assessment of visual
functions in relation to aviation duties. The medical examiner should be familiar with the visual requirements for
safe flight and other aviation functions such as air traffic control. The ordinary clinical eye examination will be
reviewed, and the requirement for special examinations in certain cases will be described. The material in this
chapter does not have any regulatory status. Its main purpose is to serve as a guide in the implementation of
the medical provisions of Annex 1. Methods are outlined for the comprehensive evaluation of the visual function
of applicants at initial and periodic re-examinations. The aim is to achieve a measure of international uniformity
of procedures and results in the assessment of both normal applicants and those in whom there is suspicion
or overt manifestation of disturbed visual function or eye disease.
11.1.2 Proper visual performance is essential for flight crew and air traffic controllers if they are to carry
out their duties safely and efficiently. In the flight environment the following factors should be kept in mind
because they may reduce visual performance significantly:
a) high speed
b) altitude
c) inadequate cockpit illumination
d) glare
e) acceleration
f) vibration
g) poor ergonomics
h) adverse cabin environment.
11.1.3 The high speeds of modern aircraft while cruising and during take-off or landing make good static
and dynamic vision and rapid reaction time particularly important. Visual perception is usually the first step in
the reflex chain which initiates the motor activity to avoid collision.
11.1.4 Altitude affects the quality and quantity of electromagnetic radiation to which the flight crew are
exposed. During flight above clouds, sunlight is reflected upwards. This inverse light distribution leaves the
instrument panel in shadow while the outside is very bright. The human visual system is designed to function
best with illumination coming from above; in some aircraft with “bubble” canopies, flight over brightly lit clouds
may be very uncomfortable. With increasing altitude the sky becomes darker, and the contrast between objects
seen against the sky increases.
III-11-2 Manual of Civil Aviation Medicine
11.1.5 In most commercial aircraft, cabin pressure is controlled but the slight degree of hypoxia
experienced even in pressurized aircraft may impair dark adaptation, reduce visual fields and visual acuity and
cause an increase in intraocular pressure.
11.1.6 In prolonged flight, the low humidity of the cabin air may cause dryness and irritation of the mucous
membranes — especially of the eyes and the nasopharynx.
11.1.7 Space myopia, empty field myopia or night myopia may occur at high altitude or at any altitude
when it is dark, owing to lack of visual targets outside the cockpit. Under low-contrast conditions a functional
myopia of up to several dioptres may occur with blurred vision and loss of contrast sensitivity. Studies have
shown that this kind of myopia is relatively common.
11.1.8 Inadequate cockpit illumination may produce visual problems. Low light levels cause reduced
visual acuity and aggravate the symptoms of presbyopia making reading of small print difficult. Coloured maps
may be difficult to see. These problems may be accentuated when red lighting is used because of the
chromatic aberration of the human eye. As much of the in-flight information in commercial aviation is gained
from instruments, the minor gain in dark adaptation level using red light or low levels of white light is generally
considered to be outweighed by the loss in overall visual performance. Furthermore, runway illumination on
international airports throughout the world has now reached levels well above the absolute threshold of light
perception. On the other hand, there are numerous situations in general aviation where some degree of dark
adaptation is necessary.
11.1.9 High acceleration forces are important in military aviation, agricultural flying and in aerobatics but
less so in ordinary commercial flying. High G-forces may produce greyout, blackout or redout depending on the
direction of the acceleration force.
11.1.10 Vibration of cockpit instruments and printed material, especially in the 22–64 Hz range, may impair
vision significantly. This is particularly troublesome in helicopters. Low frequency vibrations of 2–10 Hz
encountered in turbulence or on rough runways can also degrade vision.
11.1.11 Application of ergonomic principles and consideration of human factors have done a good deal to
improve cockpit design and facilitate information flow to flight crew. Better instrument displays and thoughtful
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