Download VISUAL ASSESSMENT OF AVIATORS

Aviation Ophthalmology
Revision lecture
Wg Cdr Malcolm Woodcock
RCDM and Worcestershire Acute
Hospitals NHS Trust
Example Question 1
• A 30-year old airline pilot attends your surgery for a
routine Class 1 aeromedical examination. He does not
wear correcting lenses. You discover on careful testing
that his vision is (right eye: 6/5) (left eye: 6/12), which
is not improved by asking him to look through a
pinhole. At previous examinations his vision has been
6/5 in both eyes. He has noticed some visual discomfort
in his left eye on eye movement but is otherwise well.
• a. The International Civil Aviation Organisation (ICAO)
and Joint Aviation Authorities (JAA) have the same
requirement for best corrected distant visual acuity in
each eye separately. What is this requirement? [1 mark]
Example Question 1
• VA must be at least 6/9 in each eye separately and
6/6 using both eyes together, with or without glasses
or contact lenses (correction).
• [Aside: Experience has shown that the main
problems encountered by monocular pilots are speed
judgement when taxiing, the assessment of wing tip
and rotor blade clearances when manoeuvring in a
confined space, and the approach and landing,
especially in a cross wind.]
Example Question 1
• You examine his fundi and note hyperaemia and oedema of the
optic disc in his left eye.
• What is this condition likely to be? [2 marks]
• Give three possible underlying causes. [3 marks]
• The pilot would like to continue flying and points out that your
Licensing Authority has, in the past, certificated professional
pilots with vision worse than his. He is operating in a large
commercial jet airliner, with two pilots.
• Would you allow him to continue flying? Justify your answer.
[3 marks]
Example Question 1
• Swollen disc (optic nerve head) NB:
Papilloedema is a specific term relating to
swollen discs secondary to raised
intracranial pressure.
• Papilloedema (BIH, brain tumour), papillitis
(MS, sarcoid, TB, syphilis, viral), ischaemic
optic neuropathy, central retinal vein
occlusion, malignant hypertension.
• Diagnosis key. Binoc VA good, likely
recovery period, ?as or with co-pilot
Example Question 1
• He is referred for neurological assessment and a
magnetic resonance image (MRI) scan is undertaken.
• What was this investigation assessing and why is it
important to know the result? [2 marks]
• After six months his visual acuity is (right eye: 6/5) (left
eye: 6/6). A subtle vision defect persists, however. Give
an example of what this defect might be. [1 mark]
• Accredited medical conclusion indicates that he can
return to flying in a two-pilot operation. What is meant
by ‘accredited medical conclusion’? [1 mark]
MRI Criteria for Brain Abnormality:
Space and Time Dissemination
•
MRI Lesions Disseminated in Space
–
–
–
–
–
•
•
MRI Lesions Disseminated in Time
–
–
–
•
•
At least three of the following criteria must be met:
One gadolinium-enhancing (active) lesion or nine T2-hyperintense lesions in the brain or
spine
At least one infratentorial or spine lesion
At least one juxtacortical lesion
At least three periventricular lesions
At least one criterion must be met:
Gadolinium-enhancing lesion ≥3 mo after initial presentation, but in a different location
from the initial event.
New T2 lesion, compared with a reference MRI done ≥30 days after onset of initial event
Reduced colour perception
Accredited medical conclusion?
Example Question 1
• He returns to flying with an “as or with co-pilot only” limitation
on his licence. Neurological follow-up is arranged.
•
Give an example of how the following might be affected in the
future and the relevance to flight safety: [3 marks each]
•
•
•
•
(1) Motor system
(2) Sensory system
(3) Autonomic system
(4) Eye movement
Example Question 1
• Motor – weakness, tremor, ataxia
• Sensory – balance (inner ear), vision,
proprioception
• Autonomic – bladder symptoms most
common, cardiovascular autonomic
alterations might relate to clinical signs
such as orthostatic intolerance
• Eye movements - internuclear
ophthalmoplegia
Example Question 2
• Write short notes on five of the following topics [5 marks each] :
•
•
•
•
•
•
•
•
a. The aspects of the aging process that are of importance in assessing
fitness to fly.
b. The management of irritable bowel syndrome in an Air Traffic
Controller.
c. The management of labyrinthitis in military aircrew.
d. The hazards of cleaning aircraft fuel tanks.
e. The management of pregnancy in a commercial airline pilot.
f. Examination of the eye following suspected LASER exposure.
Examination of the eye following suspected LASER exposure.
•
•
•
•
V and VA
Colour vision
Visual field
Fundoscopy
Example Question 3
• Write short notes on FIVE of the following [5
marks for each]:
• a. Factors which predispose to sub-atmospheric
decompression sickness
• b. The Purkinje phenomenon
• c. Active noise reduction
• d. The Push Pull effect
• e. The somatogyral illusion
• f. Negative transfer
• g. Confounding
Write short notes on the Purkinje
phenomenon (5 marks)
• A phenomenon in which all of the colours of the
spectrum do not fade equally with diminishing light. It
is actually a shift in the relative brightness of certain
colours as illumination diminishes
• When blue and red objects with the same light energy in
daylight are viewed in diminishing mesopic light levels
the blue objects will stimulate rods to a greater degree
than cones and appear to glow. Red objects tend to
darken.
• At dawn and dusk, this phenomenon can be a
troublesome for aviators as changing colour brightness
can lead to misperceptions in depth judgement.
Describe how the physiology of binocular vision
contributes towards distance and depth perception in
humans. [2 marks]
• Stereopsis (retinal binocular disparity).
Form of triangulation. Far objects have
small retinal disparity whilst near objects
have a larger disparity.
• Convergence – binocular oculomotor cue
for distance/depth perception. Kinesthetic
sensations from extraocular muscles.
Effective for distances < 10m
Discuss the importance of binocular vision in aviation
and highlight how its importance varies between fixed
wing aircraft and helicopters. [2 marks]
• Stereoscopic vision at distances up to about 50m
provides good information to judge distance. Lack of
stereoscopic vision, therefore, may cause difficulty in
judging distance (both vertical and horizontal), speed,
drift and surface texture.
• Experience has shown that the main problems
encountered by monocular pilots are speed judgement
when taxiing, the assessment of wing tip and rotor blade
clearances when manoeuvring in a confined space, and
the approach and landing, especially in a cross wind.
Describe what cues a pilot would use to judge
distance during an approach to a runway for landing
in optimal conditions. [5 marks]
• Monocular
–
–
–
–
Relative size
Perspective: parallel lines to a point on horizon
Overlapping of objects
Position in visual field: as an object moves into the distance it appears to
be closing in on the horizon.
– Aerial Perspective: a depth cue arising from Rayleigh scattering of light in
the atmosphere
– Parallax: head movement
– Motion Parallax: as observer moves
• Binocular
– Convergence/accommodation
– Stereopsis
What factors could adversely effect his/her ability to
perceive and judge distance and why? [4 marks]
• Poor illumination – reduced VA in dark conditions
• Uncorrected refractive error – reduced VA
• Different magnification of an image presented to each eye, e.g., with a
poor optical device. Magnifications < 0.5% present no problems; up to
2% can result in eye strain; 2-5% can seriously degrade stereopsis and,
> 5% can result in a temporary amblyopia.
• Different colouration an image presented to each eye. If a red filter is
placed in front of one eye and a blue one to the other eye, then the
brain has difficulty in fusing both images. In addition, chromatic
aberration effects give rise to different states of lens accommodation in
each eye, compounding the visual confusion.
• Different brightness of an image presented to each eye. If the
brightness of an image in each eye differs by greater than 10%, then
significant degradation in stereopsis occurs. In extremis, it can result in
motion illusions – the Pulfrich Effect.
Draw and label the dark adaptation curve of
the eye and explain what happens. [2 marks]

The time course of dark adaptation. The threshold in log units for vision
is plotted as a function of time in the dark. Adaptation in the normal eye
(solid curve) occurs in two phases. When colored light is used, sensation is
chromatic to the arrow, achromatic thereafter. Curve a is the adaptation
curve for a night-blind person. Curve b is the adaptation curve for a
completely color-blind person. (Gruesser O-J, Gruesser-Cornehls U:
Physiology of vision. In Schmidt RF [ed]: Fundamentals of Sensory
Physiology. New York. Springer- Verlag, 1978
How and why are colour perception and visual
acuity affected during the dark adaptation
process? [2 marks]
• Cones: trichromatic photoreceptors
concentrated in and around fovea. Require
high ambient light levels. Give high acuity
• Rods: monochromatic low light level
photoreceptors. Peripheral macula and retina.
Lower acuity levels.
• Purkinje Shift Phenomenon: Rods more
sensitive in the blue wavelength therefore
blues glow and reds darken as go into mesopic
conditions
What are the practical implications of this dark
adaptation? [2 marks]
• Changes in acuity levels and colour perception
potentially confusing in mesopic conditions.
• Ambient Red Lighting: not useful in mesopic
conditions – loose ability to rapidly change
focus, reduced colour discrimination,
decreased accommodation cues and distortion
of relative brightness can result in errors of
depth perception or lead to visual illusions
Describe both the advantages and disadvantages of
using night vision goggles (NVGs). [3 marks]
• Improve vision quality in low light levels –
increase operational effectiveness at night
• Reduced VA and visual field compared to
normal daytime operational environment.
• Magenta eye
How are each of the cues you described above used
by pilots to judge distance during an approach to a
runway for landing affected by using NVGs?
[3 marks]
• Stereopsis significantly degraded and some
monocular clues lost leading to loss of depth
perception – overestimation of clearance distances
• Reduced field with loss of peripheral cues makes
judging aircraft altitude and attitude more difficult
• NVGs focused to infinity therefore need to look
underneath them at instruments; the required cockpit
lighting can give rise to a glare source
A 32 year old military flying instructor presents with a painful red eye.
Discuss the possible diagnoses (6 marks) and how you would investigate
them (6 marks). Outline the treatment and aeromedical disposal of three
common examples (12 marks).
•
•
•
•
•
•
Anterior uveitis
HSV keratitis
Contact lens related microbial keratitis
Traumatic corneal abrasion
Episcleritis
Scleritis
A 40 year old pilot complains of the recent onset of blurred
vision in one eye. Describe your investigation and
management of the case and discuss the aeromedical
disposition. [24 marks]
•
•
•
•
HPC, PMHx, POphHx, FHx
V, VA, colour vision and field of vision
Ocular examination
Refractive error, optic neuritis, CRVO,
cataract, retinal detachment