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Part III. Medical Assessment
Chapter 11. Ophthalmology III-11-37
square with a central fixation point and the major meridians, 30 degrees apart, marked with stitching. The
applicant is seated with the eyes 1 or 2 m from the centre of the tangent screen. If distance spectacles or
contact lenses are normally used the applicant should wear these for the examination. Each eye is tested
separately while the other eye is occluded.
11.5.11 The illuminance of the screen is usually between 200 and 300 lux. Test objects are circular discs
from 1 to 50 mm in diameter, matt white on one side and matt black on the other. They are inserted in the end
of a long wand painted matt black. Battery-illuminated test objects are also available and there are projection
methods.
11.5.12 The examiner monitors the applicant’s fixation on the central spot on the tangent screen while the
test object is moved in at 30-degree intervals from the periphery towards the centre of the screen. The applicant
indicates when he first sees the test object and if it disappears at any time during transit along each meridian
tested. The normal blind spot is plotted first. This is about 6 degrees wide and is located in the temporal field
between 12 and 18 degrees from the fixation point. As a screening test a 3-mm diameter white object is
satisfactory and should be seen in all parts of the tangent screen except the normal blind spot. If a scotoma is
detected it can be further examined using different sized white targets. During the test the examiner can check
the applicant’s attention from time to time by rotating the test disc so that the black (almost invisible) surface is
presented. Failure to see a 3-mm white target in all parts of the tangent screen (except for the normal “blind
spot”) would be reasonable grounds for referral to an ophthalmologist.
Perimetry
11.5.13 This test method examines the entire visual field by measuring its extent as delineated on multiple
arcs of a circle approximately concentric with the eye. Several instruments have been devised ranging from
simple, manually operated arc perimeters which can be rotated through 360 degrees so as to allow
examination of multiple meridians using hand-held targets of different sizes to the large, expensive automated
perimeters which use projection methods of displaying the targets and which have multiple, computer-driven
test patterns and data base storage capability. The fixation of the examinee can be monitored during testing,
and the size, brightness and colour of the test object together with the background illumination can be
controlled. Instruments such as the Goldmann perimeter can be used with moving targets to determine the
different isopters (kinetic perimetry), and other instruments use stationary targets the brightness of which is
adjusted so as to determine the retinal sensitivity (static perimetry). In all cases the aim is to determine the
sensitivity of the different parts of the retina. Detailed description of the different instruments and test methods
is not necessary. The test results from modern automated perimeters are in general reliable and reproducible
but they are not infallible and some experience is necessary to interpret the results correctly.
Medical factors
11.5.14 Abnormalities in the visual fields should be distinguished from loss of peripheral vision resulting
from impaired ocular motility. True field defects can be caused by a large number of neuro-ophthalmological
disorders. Before outlining some of the more important causes of visual field defects it is worth mentioning the
so-called pseudo-field defects which can occur in the following:
a) Facial contours — prominent nose, eyebrows, cheekbones, and ptosis from any cause
b) Opacities in cornea, lens or vitreous body
c) Wearing strong spectacle prescription, especially aphakia correction
III-11-38 Manual of Civil Aviation Medicine
d) Hysteria and malingering
e) Mental deficiency, impaired cerebral function from drugs or disease, and poor understanding
of the test procedures.
11.5.15 True visual field defects are seen in trauma and congenital or acquired diseases affecting any part
of the visual pathway from the retina up to the occipital visual cortex. The location of the field defect, its shape
and whether it is unilateral or bilateral help to determine the location of the damage and in some cases are
characteristic of specific diseases or groups of diseases. Only the broadest generalizations can be mentioned:
a) Retinal or choroidal disease will give field defects which match the site of the damage
b) Macular disease will produce central scotomas while peripheral problems including retinal
detachment will cause peripheral field defects
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Manual of Civil Aviation Medicine 2(54)
