Aviation Ophthalmology

1. Aviation Ophthalmology Revision lecture Wg Cdr Malcolm Woodcock RCDM and Worcestershire Acute Hospitals NHS Trust

2. 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]

3. 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.]

4. 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]

5. 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

6. 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]

7. MRI Criteria for Brain Abnormality: Space and Time Dissemination • MRI Lesions Disseminated in Space • 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 • MRI Lesions Disseminated in Time • 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?

8. 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

9. 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

10. 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.

11. Examination of the eye following suspected LASER exposure. • V and VA • Colour vision • Visual field • Fundoscopy

12. 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

13. 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.

14. 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

15. 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.

16. 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

17. 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.

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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 aeromedicaldisposition. [24 marks] • HPC, PMHx, POphHx, FHx • V, VA, colour vision and field of vision • Ocular examination • Refractive error, optic neuritis, CRVO, cataract, retinal detachment