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11.11 CONCLUSION
11.11.1 As in all technical fields, the developments in aviation as well as medicine accelerate with each
passing year. New generations of aircraft and navigation systems together with improved instrumentation and
new ways to manage increasingly crowded airspace bring with them challenges to flight crew, ground support
staff, air traffic controllers and those charged with supporting the health of aviation workers and improving the
comfort and safety of their workplace. Improved surgical techniques and better medical management of many
disorders enable individuals who might have had to stop working in the aviation environment to continue safely
and effectively.
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Chapter 11. Ophthalmology III-11-59
11.11.2 The inevitable delay between writing and publishing means that some of the information presented
in this chapter may already be or soon will be out of date. This is most likely to occur in the sections dealing with
refractive surgery and with glaucoma medications. Updating will be required in a few years to keep pace with
further developments in medical science and to make new adjustments to the changing occupational demands
of flight crew and air traffic controllers, the paramount concern remaining the safety of aviation.
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III-11-60 Manual of Civil Aviation Medicine
ATTACHMENT
EVALUATION OF SIGNIFICANT DEFECTS OF BINOCULAR VISION
1. A significant defect of binocular vision implies either the presence of or increased risk of visual
symptoms incompatible with safe flying. In a traditional ophthalmological meaning of the terms, an applicant
may show anomalous or absent binocular vision without demonstrating symptoms significant for safe flying.
On the other hand, an applicant may demonstrate apparently normal binocular vision, which in some situation
may decompensate, resulting in symptoms incompatible with safe flying. Evaluating binocular vision in relation
to aviation medicine thus implies establishment of how the two eyes cooperate and an assessment of the
stability of this cooperation.
Normal binocular vision
2. In normal binocular vision, a viewed object is imaged in the observer’s two retinas on
corresponding retinal points, which means points having identical directional values. After this, cerebral
integration of the two images (sensory fusion) occurs so that the observer sees the object as single, at a given
distance and in a particular direction. Traditionally, the normal binocular vision is considered to have three
elements: simultaneous perception, fusion, and stereopsis.
3. The presence and maintenance of normal binocular vision requires precise coordination of the
movements of the two eyes to ensure that the object of regard is imaged on corresponding retinal points. This
is the motor component of fusion. Fusion is the blending of the visual information from the two eyes into a single,
unified perception and, as mentioned, has both sensory and motor components. The motor component can be
measured by determining the ability to overcome prismatic displacement of the retinal image in a given
direction. Such measurements of the fusional reserve are called fusional amplitudes and normally are greater
at near than at distance and much greater horizontally than vertically.
Stereopsis
4. Stereopsis is the perception of the third dimension obtained from fusible but slightly dissimilar
retinal images. It is very important for depth perception at close range but much less important at distances
beyond about 30 m and is not a requirement for safe flying.
Adaptive mechanisms
5. In manifest strabismus an object is imaged on non-corresponding retinal points and may be seen
as double (diplopia). In persons with an immature central nervous system (less than eight years of age)
cerebral adaptation generally develops to overcome the diplopia. Sensory adaptations to strabismus include
suppression (disregarding the image from the deviating eye) and anomalous retinal correspondence
(assignment of new directional values to retinal points in the deviating eye).
Suppression
6. Suppression is a positive inhibitory reflex developed to allow the visual cortex to ignore the visual
information coming from a deviating eye so as to avoid diplopia. In alternating strabismus the suppression
changes from one eye to the other depending on which eye is being used. In unilateral strabismus the
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Chapter 11. Ophthalmology III-11-61
suppression is always in the deviating eye. The size, shape and density or depth of the suppression scotoma
is different in different types of strabismus.
7. In most squinting persons with suppression, the whole area of the visual field of the deviating eye
　
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