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upwards and 75 degrees downward. These values depend to some extent on the facial configuration of the
subject. A large nose, deep-set eyes, and prominent eyebrows may influence the size of the field. Figure 11-13
illustrates the normal monocular and binocular visual fields.
11.5.4 In humans and all animals with forward-looking eyes, there is overlapping of the visual field of each
eye so that the binocular field has a central area which is seen by both eyes simultaneously and temporal
crescentic areas which are only perceived monocularly. The value of the binocular field is that it allows for
improved depth perception and gets rid of the restriction of the monocular field caused by the nose.
11.5.5 The integrity of the visual field is of special importance to flight crew and air traffic controllers. A
pilot must be aware of other aircraft and objects on the ground while scanning cockpit instruments or looking
at charts. The “peripheral flow” of visual information during the landing flare is critical for this manoeuvre.
Figure 11-13. Extent of the visual field
11.5.6 Apart from specific diseases causing visual field loss and covered in a later section, the following
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III-11-36 Manual of Civil Aviation Medicine
factors may interfere with the visual field:
a) Mechanical factors
Aircraft windshield design, nose cone and wing design, headgear including helmets and
oxygen masks and spectacle frames or multifocal segment lines are some of the impediments
to vision.
b) Physiological factors
Sources of bright light, both natural and artificial (e.g. laser emitters6), may cause strong
after-images with resulting temporary central scotomas. Some powerful lasers have the
potential to cause permanent scotomas and other eye damage. Hypoxia may cause
constriction of the peripheral visual field and enlargement of the normal blind spot, effects
which can come on rapidly and may start at altitudes as low as 1 000 to 1 500 m (3 280 to
4 921 ft).
11.5.7 Depending on the size, location and density, a scotoma in the visual field of an applicant might
represent a major safety risk.
Methods of examination
Confrontation
11.5.8 The simplest but least accurate method of measuring the visual field is by confrontation (Donders’
test7), in which the examiner compares the applicant’s visual field with his own visual field. The examiner’s
visual field must be normal. The visual field is tested for each eye separately. The examiner and applicant are
seated opposite each other about 1 m (3 ft) apart. The applicant’s left eye is occluded. The examiner closes his
right eye and each fixes the exposed eye of the other. The examiner moves a finger or a small white test object
mounted on a handle from the extreme periphery towards the midline in a plane halfway between examiner and
applicant and notes when it first comes into view. It should be seen simultaneously by the applicant. The test
object should be brought into the centre of the field and any points of disappearance and emergence noted. All
four quadrants of the visual field should be tested, exploring at least two different meridians in each quadrant.
The applicant should have his back to the light, and the background behind the examiner should be uniform
and dark, if possible. The test is repeated on the applicant’s other eye using the examiner’s other eye as the
“control”. Various modifications of this confrontation method can be used such as counting fingers in each
quadrant of the visual field.
11.5.9 If the confrontation test suggests field loss or if there are other reasons to suspect field loss such
as glaucoma, retinal or other ocular disease or neurological problems, more precise methods must be used.
Tangent screen or campimetry
11.5.10 This method is useful for detailed examination of the central 30 degrees of the visual field but
cannot be used to evaluate the peripheral field. The tangent screen is usually black felt 1.5 to 2 m (5 to 6 ft)
6 For further information on laser emitters and their effect on the visual function, see Manual on Laser Emitters
and Flight Safety, ICAO Doc. 9815
7 After Franciscus Cornelius Donders, Dutch physician and ophalmologist (1818-1889).
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