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VISION IN AVIATION

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To describe visual characteristics of the eye relevant to aviation and to discuss ocular diseases
in relation to the aviation environment
AIM

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Sight - the most important sense used in aviation
More than 80 per cent of all information acquired by pilots
from cockpit instruments and through the canopy is visual
Colour vision is an important issue in aviation as methods
of measuring it have developed
INTRODUCTION

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VISUAL REQUIREMENTS-PILOTS
VA
(uncorrected)
VA
(Corrected)
NEAR
(33cm)
REFRACTION
RANGE
MUSCLE BALANCE ACCOMODATION CONVERGENCE CP
6/6
(RN/AAC
6/12)
6/6 N5 DV 6ESO to 8EXO
1 Hyperphoria
Age 17–20 9D
Age 20–25 7D
To 10 cm or
better
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SPHERE CYL
Plano
to
+1.75
(RN/
AAC -
0.75 to
+1.75
+0.75

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HYPERMETROPIA
 MYOPIA
ASTIGMATISM
REFRACTIVE ERRORS

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HYPERMETROPIA
• Axial – Short Axial length of eye ball.
• Refractive or Index – Refractive power of eye changes.
TYPES OF REFRACTIVE ERRORS

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HYPERMETROPIA
• Manifest - The strongest convex lens correction accepted
for clear distance vision.
• Latent - The remainder of the hypermetropia, masked by
ciliary tone and involuntary accommodation, often
significant in children, and cycloplegic refraction is
necessary to measure it.
TYPES OF REFRACTIVE ERRORS

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HYPERMETROPIA
• Facultative - Overcome by accommodation.
• Absolute - In excess of the amplitude of accommodation.
TYPES OF REFRACTIVE ERRORS

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MYOPIA
• Axial - Long Axial length of eye ball
• Refractive or Index – Refractive power of eye changes
TYPES OF REFRACTIVE ERRORS

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ASTIGMATISM :
•The refractive power of the astigmatic (literally, lacking a
point) eye varies in different meridians.
• A point focus of light cannot be formed on the retina.
TYPES OF REFRACTIVE ERRORS

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REFRACTIVE ERRORS

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MANAGEMENT OF REFRACTIVE
ERRORS IN AIRCREW
CORRECTIVE FLYING SPECTACLES (CFS)
SOFT CONTACT LENSES
REFRACTIVE SURGERIES

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CORRECTIVE FLYING
SPECTACLES (CFS)
• Customized Glasses – suitable for working environment.
• Spare pair must always be carried in accessible place while
flying

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CORRECTIVE FLYING
SPECTACLES (CFS)
• Characteristic Aviator Shape
• Matt Black coated metal frames
Two Designs :
1- General-purpose frame - 9021A
2- Wrap around shape to the front for use with aircrew
respirators and the AR5 hood - 9013A

•
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CORRECTIVE FLYING
SPECTACLES (CFS)
 Type of material :
1- Low power - CR39 Acrylic
2- High power – Polycarbonate lenses (to reduce weight and
thickness of lens)
• All have anti-scratch and anti-reflection coatings

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CORRECTIVE FLYING
SPECTACLES (CFS)
 Type of lenses :
1- Bifocal
2- Trifocal
3- Progressive power
• All have anti-scratch and anti-reflection coatings

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CORRECTIVE FLYING
SPECTACLES (CFS)
 Problems
• Mechanical Failure
• Misting or Sweat accumulation
• Comfort and Safety

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AIRCREW CONTACT LENSES
• Contact lenses (CL) are the preferred option for visual
correction across the whole spectrum of aircrew tasks.
Especially in UK and US.
• The aviation environment is generally dry and hypoxic and
aircrew often work unsociable hours and are detached at
short notice to a range of physical environments

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AIRCREW CONTACT LENSES
• Daily Disposable CLs
•Silicone Hydrogel CLs
Low water Content
High Oxygen Permeable
Used for excessive Dry Eyes
Can be used for 30 days (not approved for general aircrew
use )

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AIRCREW CONTACT LENSES
 Disadvantages of CLs
Dehydration of CLs
• Surface deteriorates causing poor vision.
• Reduced blink rate due to concentration on the tasks
• The air-conditioning systems of aircraft create a dry,
hypoxic atmosphere.

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AIRCREW CONTACT LENSES
Aircrew are advised to ensure
• Adequate water intake.
• Need to blink (at least once every four seconds).
• Rewetting drops can also be used.
•NOT BEING USED IN PAK PRESENTLY

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AIRCREW CONTACT LENSES
 Disadvantages of CLs
CL Movement
• Squeeze - blink Reflex – dislocates a lens.
• Toric lens - rotates under high G conditions.
Corneal Hypoxia
Microbial Keratitis

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AIRCREW CONTACT LENSES
 Disadvantages of CLs
Presbyopia – No bifocal soft CLs

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REFRACTIVE SURGERY
RADIAL KERATOTOMY – RK
PHOTOREFRACTIVE KERATOTOMY – PRK
LASER EPITHELIAL KERATOMILEUSIS – LASEK
LASER IN SITU KERATOMILEUSIS - LASIK

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REFRACTIVE SURGERY
 RADIAL KERATOTOMY – RK
•Radial keratotomy (RK) was the first large volume surgical
treatment for myopia.
•A series of corneal cuts are fashioned in a spoke-shaped
pattern around the pupil, penetrating 85-95 percent of the
depth of the cornea.

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REFRACTIVE SURGERY
 RADIAL KERATOTOMY – RK
• The refraction changes during the day and at altitude after
RK.
• These are not desirable characteristics in aviation.
• RK has largely fallen out of favour as newer laser
techniques have been developed.

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REFRACTIVE SURGERY
 RADIAL KERATOTOMY – RK

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REFRACTIVE SURGERY
 PHOTOREFRACTIVE KERATOTOMY – PRK
•The first laser corneal refractive surgery (CRS) for myopia,
developed in the latter half of the 1980s, was photorefractive
keratotomy (PRK).
• Integrity of Globe is unaffected.

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REFRACTIVE SURGERY
 PHOTOREFRACTIVE KERATOTOMY – PRK
 DISADVANTAGES :
•Corneal Haze
•Regression of refractive correction
•10 % will lose a line of snellen acuity post op

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REFRACTIVE SURGERY
 PHOTOREFRACTIVE KERATOTOMY – PRK

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REFRACTIVE SURGERY
 LASER EPITHELIAL KERATOMILEUSIS – LASEK
• A variant of PRK, called laser epithelial keratomileusis
(LASEK, not to be confused with LASIK) also displaces a
flap of epithelium, which is replaced after the laser
procedure and acts as a bandage.

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REFRACTIVE SURGERY
 LASER EPITHELIAL KERATOMILEUSIS – LASEK
• Recovery is faster and less painful with this modification
than with standard PRK.
• The visual outcome is very similar to PRK and LASIK but
the pain of PRK is minimized.
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REFRACTIVE SURGERY
 LASER EPITHELIAL KERATOMILEUSIS – LASEK

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REFRACTIVE SURGERY
LASER IN SITU KERATOMILEUSIS –
• It is a popular refractive surgical technique.
• It involves the cutting of a 100–160 micron flap of corneal
tissue and ablating the underlying stromal bed, before
replacing the flap .
• Minimum Pain
• Visual Recovery – 1 to 2 days

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REFRACTIVE SURGERY
 DISADVANTAGES OF LASIK :
•Night Vision abnormalities
•Loss of Contrast Sensitivity ( haloes and starbusrts around
light sources)
•Dry Eyes – 6 months post op

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REFRACTIVE SURGERY
LASER IN SITU KERATOMILEUSIS –

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REFRACTIVE SURGERY
Other Modalities :
Wavefront abberometry :
• Very accurate results
• Less night vision abnormalities
• Also addresses high orders of ametropia

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REFRACTIVE SURGERY
Other Modalities :
Femtosecond Laser :
A new type that can cleaave the layers of the cornea. It
fashions thin flaps that sit well on the cornea and is
commonly used in LASIK. The technique is popular and is
developing into a standard method of delivering LASIK.

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OPHTHALMIC HISTORY AND
EXAMINATION
 Detailed Questionnaire relating to
• Past Ophthalmic diseases
• Need or use of Refractive Correction
• Family History

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OPHTHALMIC HISTORY AND
EXAMINATION
Visual Acuity –Distance
 Backlit Snellen Chart at 6 metres
 Paient must not be wearing contact lenses
 Patient must not be squeezing eyes
 Lowest line that is read correctly and completely

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OPHTHALMIC HISTORY AND
EXAMINATION
Visual Acuity -Distance
 Errors in measuring Visual Acuity
• Wrong Distance
• Too much Light causing Glare
• Memorisation of letters so different chart face used each time
• Eyes should not be pressed as it can temporarily alter the shape
of Cornea
• Should not narrow the Palpebral Fissure

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OPHTHALMIC HISTORY AND
EXAMINATION
Visual Acuity - Near
 Uniocular and Binocular
 Tested with normal Reading Correction
 Distance 33 cm

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OPHTHALMIC HISTORY AND
EXAMINATION
Testing for Hypermetropia
 Manifest Hypermetropia
 The highest power of Plus lens through which the 6/6 Snellen
line can be read quickly and correctly
 Important to identify individuals with Manifest Hypermetropia
as they use accomodation and they will become Presbyopic and
then Hypermetropic by middle age

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OPHTHALMIC HISTORY AND
EXAMINATION
Testing Accomodation
 Using RAF near point rule
 The drum with near test type is used
Testing Convergence
 Using line and dot test on RAF near point rule
 Subjective vs Objective Convergence

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OPHTHALMIC HISTORY AND
EXAMINATION
RAF RULE NEAR VISION DRUM

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OPHTHALMIC HISTORY AND
EXAMINATION
Stereopsis
 Ability to obtain an impression of depth by
superimposition of two images
 Toegepast Natuurwetenschap Onderzoek (TNO) random
dot stereogram stereo test is used
 7 plates viewed with red-green spectacles
 Hidden shapes which are only apparent when spectcales
are worn and stereopsis is present.

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OPHTHALMIC HISTORY AND
EXAMINATION
Stereopsis
 Ability to obtain an impression of depth by
superimposition of two images
 Toegepast Naturwetenschap Onderzoek (TNO) random dot
stereogram stereo test is used
 7 plates viewed with red-green spectacles
 Hidden shapes which are only apparent when spectcales
are worn and stereopsis is present.

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OPHTHALMIC HISTORY AND
EXAMINATION
Testing ocular muscle balance
 Orthophoria
 A state of ocular balance with image fusion without
effort
 Ocular imbalance results in varying degrees of squint or
strabismus (tropias or phorias)
 This can result in Diplopia (double vision)

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OPHTHALMIC HISTORY AND
EXAMINATION
Testing ocular muscle balance
 Orthophoria
 A state of ocular balance with image fusion without
effort
 Ocular imbalance results in varying degrees of squint or
strabismus (tropias or phorias)
 This can result in Diplopia (double vision)

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OPHTHALMIC HISTORY AND
EXAMINATION
Maddox Wing
 Dissociates the two eyes for near fixation at 33 cm
 Right eye sees a white vertical arrow and red horizontal
arrow
 Left eye sees a horizontal and vertical row of numbers
 Horizontal deviation is numbers white arrow pointing to
 Vertical deviation is numbers red arrow pointing to

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OPHTHALMIC HISTORY AND
EXAMINATION
MaddoxWing
 Dissociates the two eyes for near fixation at 33 cm
 Right eye sees a white vertical arrow and red horizontal
arrow
 Left eye sees a horizontal and vertical row of numbers
 Horizontal deviation is numbers white arrow pointing to
 Vertical deviation is numbers red arrow pointing to

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OPHTHALMIC HISTORY AND
EXAMINATION
Colour Vision
 Colour defective pilots have significantly reduced target
acquisition and lower reaction times to coloured visual
stimuli
 Colour deficiency can be Congenital or Acquired

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OPHTHALMIC HISTORY AND
EXAMINATION
Congenital Red/Green deficiency
 Sex linked
 8 % of males and 0.4% of females
Protanomaly
 Deficiency of red cone type
 1 % of males

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OPHTHALMIC HISTORY AND
EXAMINATION
Dichromat
 Completely colour blind
 Lacks two cone types
Protanope
 Lacks red cone type
 1 %

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OPHTHALMIC HISTORY AND
EXAMINATION
Deutranomaly
 Deficiency of green cone type
 5 - 6 % of males
Tritanomaly
 Deficiency of blue cone type
 0.002 – 0.007 % of population

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OPHTHALMIC HISTORY AND
EXAMINATION
Deutranope
 Lacks green cone type
 1 %
Tritanope
 Lacks blue cone type
 0.002 – 0.007 %

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OPHTHALMIC HISTORY AND
EXAMINATION
Acquired Colour Defects
 5 – 15 % of population
 Drugs include oral contraceptives, oral diabetic agents,
tetracyclines, antimalarial drugs, digoxin, ethanol,
tobacco, Viagra and thiazide diuretics

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OPHTHALMIC HISTORY AND
EXAMINATION
Viagra (Sildenafil)
 Marked effect on blue yellow colour discrimination
 Gives a bluish tinge
 Effects last for between 1 and 6 hours
 An aviator who uses this drug must not fly for 24 hours
after ingestion

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ELECTRONIC FLIGHT
INSTRUMENTATION SYSTEM
 Allows colour coded alphanumerical and analogue data
for flight management and control
 Polychromatic data using more than 8 colours
 Examples
• Yellow colour for power information
• Magenta for track or trajectory processing

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MEASURING AND GRADING
COLOUR PERCEPTION
 Congenital red/green colour deficiency is tested
 Ishihara chart is used with standard 24 plates
 If correct numbers are identified, the individual is declared
CP2 colour normal and no further testing is required
 If Ishihara plate test is failed, the Holmes-Wright Lantern
(type A) is the approved occupational colour vision test for
military aviators

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MEASURING AND GRADING
COLOUR PERCEPTION
 Conenital red/green colour deficiency is tested
 Ishihara chart is used with standard 24 plates
 If correct numbers are identified, the individual is declared
CP2 colour normal and no further testing is required
 If Ishihara plate test is failed, the Holmes-Wright Lantern
(type A) is the approved occupational colour vision test for
military aviators

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MEASURING AND GRADING
COLOUR PERCEPTION
Holmes-Wright lantern (type A) test
 The individual has to tell the difference between red,
green and white lights at different brightness and is a
sensitive screen test for red/green colour deficiency
 The lantern is used at 6 metres in a darkened room and
two lights, one above the other, are presented to subject
wearing normal spectacle correction

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MEASURING AND GRADING
COLOUR PERCEPTION
Holmes-Wright lantern (type A) test
 If no mistakes are made, the individual is declared CP3
colour safe
 If there is any red/green confusion, the subject is
automatically failed and is declared CP4 colour unsafe
 If there are any other mistakes in round one, two extra
runs are performed.
 If no mistakes are made, the individual is passed as CP3

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MEASURING AND GRADING
COLOUR PERCEPTION
Holmes-Wright lantern (type A) test
 If there is any mistakes in second or third round other
than red/green confusion, the individual is dark adapted
for 20 mins and test is run and if passes, is declared CP3
colour safe and if fails, is classes CP4 colour unsafe
 CP1 is when individual passes this test in a light room with
a device set on low brightness and is an Entry standard for
Royal Naval Aviation
 But this test is becoming outdated

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MEASURING AND GRADING
COLOUR PERCEPTION
Colour vision assessment and diagnosis (CAD) System
 It accurately measures the threshold for perception of
red/green and yellow/blue colour signals.
 It uses continuously changing background to mask
luminance cues (dynamic luminance contrast noise)

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OPHTHALMIC HISTORY AND
EXAMINATION
Visual fields
 There is no set minimum visual field for aviation; any
visual field loss is assessed on an individual basis

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OCULAR DISEASES
BLEPHARITIS:
Inflammation of eyelid margins
• Anterior
• Posterior

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OCULAR DISEASES
CHALAZION :
• A chronic inflammatory lesion caused by blockage of
one of the gland orifices with stagnation of the
sebaceous secretion.
• Painless firm round lesion

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OCULAR DISEASES
EPIPHORA :
Excessive watering from eyes
•Overproduction
•Obstructive

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OCULAR DISEASES
ORBITAL BLOW OUT FRACTURE :
•A sudden increase in the orbital pressure by a striking
object that is greater than 5 cm in diameter such as a
fist or a tennis ball.

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OCULAR DISEASES
EPISCLERITIS :
It is an idiopathic inflammation of the episcleral layer
of the conjunctiva
Two types - simple or nodular
Topical steroids or Topical non-steroidal anti-
inflammatory drugs may be helpful.

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OCULAR DISEASES
RECURRENT EROSION SYNDROME :
• This is a condition where the corneal epithelial
basement membrane complex is damaged by an initial
episode of superficial corneal trauma, especially from
a scratch.

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OCULAR DISEASES
RECURRENT EROSION SYNDROME :
• This is a condition where the corneal epithelial
basement membrane complex is damaged by an initial
episode of superficial corneal trauma, especially from
a scratch.

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OCULAR DISEASES
RECURRENT EROSION SYNDROME :
• Typically recurrent pain on waking with lacrimation,
photophobia and blurred vision.
• In mild cases, these symptoms resolve
spontaneously within a few hours.
• It is recurrent and may cause problems for months or
even years.

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OCULAR DISEASES
KERATOCONUS:
ADENOVIRAL KERATOCONJUNCTIVITIS
UVEITIS
•