Optometry and Ophthalmology in Aviation

Dip Optom (SA), TMOD (US), CAS (US), FC Optom (UK), PhD (Aston), FSLS, FOA(SA), FICLS

Member of Aeromedical Committee SACAA

dirk@dirkbooysen.co.za

All DAMES should understand the visual environment in which aviation personnel work!

Visual Flight deck & ATC tasks

ATC specific visual tasks

• ATC’s deal with, distance, intermediate, and near tasks
• Working in the tower requires good distance visual acuity to identify aircraft in the circuit
• Often the radar images use high resolution color coding to identify different aircraft

Medical certification, 4 classes

Class 1	Class 2	Class 3	Class 4*
ALTP	Private pilots	ATC	Recreational pilots
CPL	Student pilots	Drone Pilots	ATC assistants
Flight test ratings	Cabin Crew Members		*Medical examination can be performed by any medical doctor
Flight engineers

General – Visual System

An applicant may not have –

1. Any condition or congenital abnormality of either eye or its attachments likely to impede the safe exercise of the privileges of the licence;
2. Any abnormality of visual fields or significant defect of binocular function;
3. Any manifest squint, or large errors of eye muscle balance (phoria);
4. Any anatomical or functional monocularity or substandard vision in one eye at initial issue of a Class 1 medical certificate. However, medical conclusion may permit experienced licence holders who develop monocularity or substandard vision to be granted a medical certificate with appropriate restrictions after an adaptation period of at least six months following the loss of vision.

Visual Standards

	Class 1	Class 2	Class 3	Class 4
Distance vision	At 6 meters, 6/9, 20/30, 0.66 in each eye or better, and binocularly 6/6, 20/20, 1.0 or better with or without corrective lenses	At 6 meters, 6/12, 20/40, 0.50 in each eye or better, and binocularly 6/9, 30/30. 0.66 or better with or without corrective lenses	At 6 meters, 6/12, 20/40, 0.50 in each eye or better, and binocularly 6/9, 20/30, 0.66 or better with or without corrective lenses	At 6 meters 6/12, 20/40 , 0.50 in each eye or better, and binocularly 6/12, 20/40, 0.50 with or without corrective lenses
Intermediate vision	Read N14, 6/30, 20/100, 0.20 at 100 cm or have equivalent monocular acuity of 6/24, 20/80, 0.25 at 100cm	Read N14, 6/30, 20/100, 0.20 at 100 cm or have equivalent monocular of acuity 6/24, 20/80, 0.25 at 100cm	Read N14, 6/30, 20/100, 0.20 at 100 cm or have equivalent monocular acuity of 6/24, 20/80, 0.25 at 100cm	Read N14, 6/30, 20/100, 0.20 at 100cm or have equivalent monocular acuity of 6/24, 20/80, 0.25 at 100cm
Near vision	Read N5, 6/9, 20/30, 0.66 at a distance of 33 cm or have equivalent monocular acuity of N6, 6/12, 20/40, 0.50 at 33cm	Read N5, 6/9, 20/30, 0.66 at a distance of 33 cm or have equivalent monocular acuity of N6, 6/12, 20/40, 0.50 at 33cm	Read N5, 6/9, 20/30, 0.66 at a distance of 33 cm or have equivalent monocular acuity of N6, 6/12, 20/40, 0.50 at 33cm	Read N5, 6/9, 20/30, 0.66 at a distance of 33 cm or have equivalent monocular acuity of N6, 6/12, 20/40, 0.50 at 33cm

If uncorrected distance VA is worse than 6/60 in either eye, the applicant must provide a full ophthalmic report prior to initial assessment, and then every 5 years thereafter

Diopter Limits

• A need for corrective lenses for either eye within the range of plus or minus 5 dioptres (spherical equivalent) may be accepted, provided that the visual acuity without correction is not worse than 6/60 in each eye separately.
• Spectacle lenses outside this range are not routinely acceptable, but medical conclusion may permit an applicant to be assessed as fit on production of satisfactory specialist reports.
• The medical certificate will be, where appropriate, endorsed with the following:
  1. “Contact lenses only must be worn”; and
  2. “Spare spectacles must be readily available”.

Minimum restrictions for monocularity, amblyopia and substandard vision in one eye

• Any anatomical, functional monocular or substandard vision in one eye at initial issue of medical certificate
  • Monocularity means vision can not be corrected to 6/24, 20/80, 0.25
  • Substandard vision in one eye means central vision better than 6/24, 20/80, 0.25 but worse than 6/9, 20/30, 0.66 with normal visual fields
• Experienced license holders that develop monocular or substandard vision in one eye may be granted certification with appropriate restrictions

1. Protective goggles in open cockpit aircraft must be used
2. Accompanying pilots must be made aware of the holders monocular or substandard vision in one eye
3. Not valid for PIC by day or night until an appropriate flight test has been completed
4. No active ocular pathology present
5. Distance vision (corrected or uncorrected) must be 6/6, 20/20, 1.0 or better and near vision 6/9, 20/30, 0.66 or better

Contact Lenses

Applicants may use contact lenses to meet visual requirements, provided that:

1. the lenses are monofocal/single vision and non-tinted (no bifocal or monovision allowed);
2. the lenses are well tolerated;
3. And a pair of suitable correcting spectacles is kept readily available during the exercise of the licence privileges.
4. Applicants who use contact lenses may not need to have their uncorrected visual acuity measured at each re-examination provided the history of their contact lens prescription is known.
5. Applicants with a large refractive error shall use contact lenses or high-index spectacle lenses to correct their vision to acceptable standards
6. Finally, the applicant shall be required to have normal fields of vision as well as normal binocular function.

VA measures taken at distances beyond 2 meters are directly comparable and should show consistent values independent of the distance. Diseases and refractive errors were not shown to impact on the VA results at different distances

November 2018. Effects of Testing Distance on Visual Acuity Measures. [online]

Keystone Vision Screener (Orthorator)

Titmus V2 Vision Screening with Aeromedical Test Slide Package

Problems with Keystone and Titmus Stereoscope Screening Tests

• High False Positive Rate: They identify individuals as having a vision problem when they do not.
• Calibration and Training: For the tests to be valid and accurate, the instruments must be properly calibrated and the screening personnel must be carefully trained on the correct procedures and instructions provided by the manufacturer
• Limited Scope: Vision screening is not a diagnostic tool; it identifies potential issues that require further examination.
• High Costs: Compared to simpler methods like the Snellen chart and Pocket screener, these stereoscopes have higher equipment and maintenance costs, contributing to the overall cost of vision screening programs.
• Inappropriateness for Certain Age Groups: Some protocols suggest they are not suitable for children five years and younger.

Latent Strabismus/Heterophoria

Heterophoria Types, Features and Causes

	Type	Details	Causes
Esophoria Eye moves nasally under cover	Convergence excess	Greater at near than at distance	• Anatomical (narrow PD) • Refractive (high hypermetropia) • High AC/A ratio • Weak divergence (negative fusional reserve)
	Divergence weakness	Greater at distance than at near
	Non-specific	Similar angle at near and distance
Exophoria Eye moves temporally under cover	Convergence weakness	Greater at near, often but not always with convergence insufficiency	• Anatomical (wide PD) • Refractive (myopia, presbyopia) • Weak convergence (positive) fusional reserves • Age
	Divergence excess	Greater at distance than near
	Non-specific	Similar angle at near and distance
Vertical phoria Eye moves up or down under cover	Hyper/hypo	One eye rotates upwards and the other downwards under cover	• Refractive (high myopia)
	Alternating hyper/hypo	Either eye moves upwards/ downwards under cover	• Weak vertical fusional reserves • Anatomical (abnormal extraocular muscles) • Incomitancy – extraocular muscle anomaly
Cyclophoria Either eye “wheel rotates” under cover	Incyclophoria	Upper end of vertical axis is nasal	• Oblique astigmatism
	Excyclophoria	Upper end of vertical axis is temporal	• Incomitancy

SACAA Minimum standards for heterophoria

• SACAA – Acceptable limits are DV – 5∆ exophoria, 10∆ esophoria, 2∆ hyperphoria, 1∆cyclophoria, measured with best spectacle correction
• Ernstig’s Aviation Manual – DV 6∆ esophoria, 8∆ exophoria, 1∆ hyperphoria and NV – 6∆ esophoria, 16∆ exophoria, 1∆ hyperphoria

Heterophoria Evaluation – Maddox Rod

Cover Test and Alternating Cover Test

Causes of Heterophoria Decompensation

Optical	Medical	Environmental
Uncorrected refractive error • Esophoria decompensated by uncorrected hypertropia • Exophoria decompensated by uncorrected myopia	Poor health, fatigue, worry and anxiety • Reduces fusional reserves • Reduces amplitudes of accommodation and subsequent accommodative convergence	Increase in ocular activity • Change in occupation • Extended period of work at a particular distance
Over/under corrected refractive error • Reduces the acuity and dissociates the eyes • More pronounced where one eye is affected more than the other	Traumatic injuries • Head trauma can result in temporary or permanent reduction in fusion	Poor working environment • Reading at too close a distance for long periods • Poor illumination or contrast of visual task
Poorly fitted spectacles • Particularly with high refractive errors that can induce unwanted prismatic effects	Adverse effects of drugs • Certain anti-hypertensive and anti- depressant agents can reduce accommodation • Alcohol has been found to reduce horizontal fusional reserves	Playing games • Video games that involve rapid, repeated pursuit fixation movements • ‘Magic Eye’ 3D auto stereograms that dissociate and disrupt accommodation and convergence • VR or virtual reality devices
Anisometropia • Difference in image size between the eyes (aniseikonia) makes fusion difficult.	Short period of occlusion • Patch worn over one eye following a corneal injury • Patch worn in childhood for the treatment of amblyopia	Night driving • Reduced visual information prevents binocular functioning between the eyes
	Extensive visual field loss • Glaucoma reduces binocular matching between the eyes • Advanced AMD in one eye	Extensive monocular viewing • Jewellers • Watch makers

Visual Fields

Color Perception Standards – SACAA

• Applicants must demonstrate ability to readily perceive colors that necessary for the safe performance of duties
• Ishihara 24 (or 38) plate done in daylight or light source (C, D) specified by the ICI
• Considered passed if less than 2 errors in plates 1-15(24) and 4 errors in plates 1-21(38)
• Failing the 24 or 38 plate Ishihara test, assessed fit if they pass CAD – Color Assessment Diagnosis
• Class 1, class 2 with CVD will be allowed with restrictions on PPL, no night flight, no glass cockpit

Colour in Context

Visual perception of colour involves a complex series of events and is affected by many variables such as:

• Level of ambient illumination
• Stimulus brightness, saturation
• The influence of adjacent colours, stimulus size, shape, texture and duration
• Visual fatigue and afterimages
• The integrity of the visual system (as affected by age, disease and drug usage)

Prevalence of congenital CVD

Evaluation of CVD

• CVD can be assessed qualitatively and quantitatively
• Efficiency of the tests are based on their sensitivities and specificities
• No single test has ever reliably matched colour vision deficiency with performance degradation on specific in-flight tasks
• Colour environment in modern cockpits more challenging than before – more appropriate screening tests are required
• Six main categories
  1. Plate tests – Ishihara is the gold standard for screening
  2. Arrangement tests
  3. Lantern tests
  4. Anomaloscope
  5. Electroretinography
  6. Computer based colour vision tests – CAD,

Ishihara test

• Normal trichromats failing IT have been termed “pigment farbanomaly” – fail printed test but not spectral tests
• IT remains the “gold standard” for rapid identification of congenital red-green CVD
• Individual plates are 85% sensitive and 95% specific for R/G CVD – test as a whole performs close to 100% sensitive and specific
• Ishihara is considered passed if the candidate makes less than 2 errors on plates 1-15 (24 plate test) and less than 4 errors on plates 1-21(38 plate test)
• If the candidate fails further investigation should be carried out – CAD at SACAA

Problems with Current Secondary CVD Tests

• No test, including Ishihara* and anomaloscope**, assesses severity of colour vision loss
• Pass/fail variability (within-subject and inter-subject) is high*
• Lack of standardisation
• Correlation between outcomes of different tests is poor*
• Do not give reliable information about safe, minimum colour vision for flying

*Squire TJ, Rodriguez-Carmona M et al (2005). Color vision tests for aviation: comparison of the anomaloscope and three lantern types. Aviat. Space Environ. Med. 76, 421-429. 2 Barbur
**JL, Rodriguez-Carmona M et al (2008). A study of unusual Rayleigh matches in deutan deficiency. Visual Neuroscience 25, 507-516

Safety Critical Colour Discrimination Tasks in Aviation

Tasks with no redundancy (other cues):

• PAPI – Colour perception has to be accurate and fast
• Parking lights (much less hazardous)

Tasks with more redundancy or that are less demanding in terms of colour perception:

• Runway threshold, centre-line, lead-off, taxiway, stop way lights
• Navigation lights
• Rotating beacons on ground vehicles
• EFIS, maps, VASIS

Color Assessment and Diagnosis test

• The CAD test determines the threshold for perception of R/G and Y/B colour signals and quantifies the severity of colour vision using an internationally recognised colour system
• CAD has 100% specificity and 100% sensitivity for assessing whether an individual has normal colour vision (ie is a normal trichromat or not)
• CAD can quantify the severity of colour vision loss and it cannot be learnt
• Results are expressed in standard normal units, easy to understand, providing an immediate indication of the severity of the colour vision loss
• Useful in assessing changes in colour vision in subjects with diseases of the retina and optic nerve and to specify colour vision requirements in occupational environments

Barbur et al, Proc. Roy. Soc.B., 258, pp 327-334, 1994.

Why such stringent color standards?

Challenges facing the color-defective pilot

• Complex color-based environment
• Extreme demands on the visual system
• Must be closer to the target to discriminate it based on color information
• Take longer to interpret color-based information

FedEx 1478, 2002 struck trees on final approach to Tallahassee- first officer (flying at the time) color deficient – could not interpret the PAPI indicator – contributing to the accident

Operational colour vision test (OCVT) & Medical practical flight test (PMFT)

• The PMFT shall be conducted in a Level C or D simulator, or such lessor device as determined by the Director
• Conducted by a panel of specialists appointed by the Director and will be coordinated by authorised officers (medical assessors) of the SACAA;
• Panel shall comprise of the following: A representative authorised officer from the CAA; A designated aviation medical examiner, preferably with experience in flying; An ophthalmologist; A designated flight examiner as determined by the Director;
• The procedure for the medical practical flight test shall be approved by the Director
• Applicants must demonstrate the following: Must read and correctly interpret in a timely manner aviation instruments or displays, particularly those with coloured limitation marks; Must read and interpret coloured instrument panel lights, especially marker beacon lights, warning or caution lights, weather displays, etc.;
• Must recognise terrain and obstructions in a timely manner, have the applicant select several emergency landing fields, preferably under marginal conditions, and describe the surface; Must visually identify in a timely manner the location, colour and significance of aeronautical lights.
• Applicants will be afforded a single opportunity for a medical practical flight test.

Considerations for applicants with Class I who fail a CAD and pass the OCVT and PMFT tests

To fly as CPL in a multi-crew environment by day and night as a deuteranope with the following restrictions:

• The holder does not meet the ICAO medical standard as per Annex 1 and is therefore restricted to fly within the South African borders on a South African registered aircraft only
• Applicants who fail the CAD will not qualify for Air Transport Pilot Licence operations.
• Annual ophthalmological assessment will be required to determine any refractory, visual field or lens translucency change every two years if < 40 years and annually if > 40 years.
• The applicant must inform his/her employer and cockpit crew members of his/her red-green colour deficiency.
• The holder is restricted to a cabin altitude of maximum 8000 ft AMSL at night or during IFR conditions.
• The holder may not perform any CAT II approaches.
• A minimum required flight hours as prescribed in SA-CARS/CATS Part 61 will be applied before allowing the applicant as PIC with CPL.
• The decision and restrictions will be reviewed, should there be a change in the applicant’s condition or new evidence becomes available regarding deuteranopia and flight safety

Common ophthalmic conditions in aviation

• Conjunctivitis
• Cases should be assessed individually. Viral conjunctivitis is associated with sore throat and lymphadenopathy and is infectious. Conjunctivitis often requires topical medication (e.g. antibiotic drops) and can impact on certification when purulent secretions are copious or when drop administration is very frequent. Please note that topical eye ointments may cause reduced vision for a period after application.
• Minor eyelid infections
• Blepharitis, meibomian cyst (chalazion) or stye (hordeolum) do not normally impact on certification unless they cause discomfort or reduction in vision (e.g. due to mechanical ptosis or induced astigmatism). Topical treatment with warm compresses and topical medication, if required, can present practical problems with a busy flying schedule and so cases should be assessed individually.
• Keratitis
• Certificate holders should be assessed as unfit on diagnosis. Restoration of fit status can be considered once the condition has resolved and the applicant has stopped all medication, or occasionally when it is accepted that the condition requires low dose maintenance topical therapy.
• Anterior Uveitis
• Certificate holders should be assessed as unfit on diagnosis. Restoration of fit status can be considered once the condition has resolved and the applicant has stopped all medication, or occasionally when it is accepted that the condition requires low dose maintenance topical therapy. Consideration should be given to underlying causes (such as ankylosing spondylitis), especially if the uveitis is recurrent.
• Posterior Uveitis
• This is associated with underlying disease (inflammatory bowel disease, sarcoidosis, etc). Certificate holders should be assessed as unfit on diagnosis and a formal consultant ophthalmologist report is required (see CAA’s guidance on ophthalmic reports) and should include the results of all systemic investigations. A return to fit status should be considered bearing in mind visual function, medication and identification and control of any underlying cause.
• Trauma
• Eye injuries sufficiently severe to require medical attention will require a formal ophthalmological report. Cases should be assessed individually and suspension of the validity of the medical certificate may be required. Class 1 and 3 holders may be required to undertake assessment with a consultant ophthalmologist.
• Cataract
• This is compatible with fit status provided that: visual standards are met; and there are no symptoms of glare, halos etc.
• Retinal Detachment
• Certificate holders should be assessed as unfit on diagnosis. Consultant ophthalmologist reports will be required. Restoration of fitness status is possible provided that the effect on visual function is such that the visual standards are met. Peripheral retinal tears treated successfully with laser can be considered for restoration of fit status following recovery from successful treatment. In complex retinal detachment resulting in loss of peripheral field, certification should be discussed with a CAA Medical Assessor.
• Central Serous Retinopathy
• Certificate holders should be assessed as unfit on diagnosis. Restoration of fitness status is possible when the condition has resolved or when no further improvement to vision is expected provided that the visual standards are met. If necessary, please also refer to the substandard vision in one eye guidance.
• Acquired Disorders of the Macula
• Certificate holders should be assessed as unfit on diagnosis as macular disorders can cause significant distortion (metamorphopsia) without necessarily reducing vision to below acceptable limits. Fitness may be reconsidered when ophthalmological reports are received. Restoration of fitness will be considered on an individual case basis as there is such a wide spectrum of macular disease severity. If necessary, please refer to the substandard vision in one eye guidance.
• Glaucoma and Ocular Hypertension
• The initial diagnosis should be reported to the CAA/AME and visual function assessed. In uncomplicated cases routine follow up reports (including visual fields) can be taken to the AME at each medical. In severe cases, please refer to the visual field and substandard vision policies, as well as the guidance on eye surgery. Applicants with any form of open or closed angle glaucoma may be considered for certification provided that the consultant ophthalmology reports confirm an acceptably low rate of recurrence.
• Vascular occlusions Including – retinal artery occlusion, ischemic optic neuropathy, amaurosis fugax, and retinal vein occlusion.
• Pilots with arterial vascular disease affecting the eye should be made unfit. The subsequent aeromedical fitness assessment needs to take into account both the effect on visual function and the cardiovascular incapacitation risk.
• It is important to identify disease due to emboli from the left side heart and carotids, as this carries a higher cardiovascular risk. Infective endocarditis and the systemic vasculitis’s, including giant cell (temporal) arteritis and thrombophilia must all be excluded, as these conditions have their own treatment protocols and aeromedical implications.
• Arterial vascular disease affecting the eye is usually associated with an increased cardiovascular mortality. Cardiovascular risk factors must be identified and managed before re-certification.
• Pilots with retinal vein occlusions (RVO) should be declared unfit. The subsequent aeromedical fitness assessment needs to take into account both the effect on visual function and the cardiovascular incapacitation risk. RVO reduces visual acuity and field of vision in the affected eye, sometimes permanently.
• RVO is usually associated with an increased cardiovascular mortality. High blood pressure is a cardinal risk factor for RVO and satisfactory blood pressure control is therefore essential before re-certification.

Diagnosis and Classification

• Both changes on the posterior corneal surface and alteration in the corneal thickness progression are necessary to diagnose early stages of KC
• Tomography (Scheimflug and OCT) and slit-lamp examination are currently the best and most widely available tests to diagnose early KC
• A “gold standard” classification for KC is not currently available
• The often used Amsler-Krumeich classification system is limited, additional information including visual performance (BVA) correlated with corneal topometric and tomographic parameters may improve the classification and diagnosis of KC

Progression

• Ectasia progression is defined by a consistent change in at least 2 of the following parameters

1. Steepening of the anterior corneal surface
2. Steepening of the posterior corneal surface
3. Thinning and or an increase in the rate of corneal thickness change from the periphery to the thinnest point

• Although VA often decreases with progression, changes in uncorrected and corrected VA is not required to document progression

Non-surgical treatment options (Gomes, Tan et al. 2015)

Ophthalmic drugs in aviation

Glaucoma drugs in aviation

Increased minus or plus spectacle power

Selective filters

Blue blockers and yellow lenses interfere with color perception, therefore not allowed

SACAA Ophthalmology Report Template

• Aviator or applicants name, licence class and age
• History
  Systemic and ophthalmic
• Vitals
  Visual acuity with and without correction
  Pupil reactions
  Intra ocular pressure and method used to measure it (GAT, NCT and RBT)
• Refractive status
• Eye movement and alignment – strabismus or phoria and size of deviation if any
• Anterior segment evaluation – lids, adnexa, conjunctiva, cornea, anterior chamber and crystalline lens
  Corneal topography and tomography scans if available
• Posterior segment evaluation – ocular media, macula, disc, mid periphery and periphery
  Fundus photos, ocular coherence tomography, and visual field tests if available
• Diagnosis, prognosis and treatment plan

Thank You

dirk@dirkbooysen.co.za