Physiology Of Vision

Question 1

Importance of vision in Aviation

Answer 1

80% of spatial orientation cues
Visual scanning
Collision avoidance
Depth and distance perception
Situational awareness

Question 2

What threats degrade visual performance in military aviation?

Answer 2

Physiological threats
- G force, fatigue, hypoxia, medical conditions, medication
Physical threats
- Lasers, bird strike, MDC splatter, wind blast, glare, UV radiation, ionising radiation, NVGs

Question 3

Role of cones in focal vision and its weaknesses

Answer 3

High visual acuity
Colour vision
Fine detail
High definition

Not good at 
Needs lots of light
Night blind spot 
Conscious awareness of gaze
Small area of visual field

Question 4

Role of rods in peripheral vision and its weakness

Answer 4

Sensitive to low light
Sensitive to movement
Horizontal reference
Works without conscious awareness

Weakness
Low visual acuity
Poor colour vision
Orientation information from external visual references

Question 5

Types of depth perceptions and their cues

Answer 5

Binocular

• convergence - muscle (6m)
• Stereopsis - distance on retina (>6m to 200m)
• Accommodation - lens (6m)

Monocular cues - distance

• Size constancy
• Aerial perspective - blue in distance
• overlap
• linear perspective - parallel line move closer together
• relative motion

Question 6

Physiological limitation of visual performance

Answer 6

Focal traps
Empty field myopia
Threshold for acuity
Saccadic vision
Cues of dept perception
Anatomical blind spot
Physiological blind spot
Perception time

Question 7

Explain Focal traps

Answer 7

Chip on windscreen
Focus on the foreground
Functionally myopic

Question 8

Define empty field myopia

Answer 8

Rest position of gaze is 1-2 meter

Functional myopia, can’t see distance

Question 9

Threshold of acuity

Answer 9

6/60 minimal distance

Question 10

Saccadic eye movement

Answer 10

Rapid flicking movement of eyes
Blurs retinal image
Targets may not be perceived

Question 11

Limitation of depth perception

Answer 11

Binocular cues - limited by distance

Monocular - misperceptions based on learned cues and expection

Question 12

Illusions from focal or peripheral vision

Answer 12

Focal - Absent or inadequate visual cues, Errors of top down processing
Peripheral - False horizons, illusion of movement (vection)

Question 13

What are illusions from central visual processing

Answer 13

Brown out
White out
Terrain shadows and illumination
Night illusion

Question 14

Illusions from peripheral vision

Answer 14

False horizons

• sloping cloud tops
• ground lights
• Coastlines
• Sloping terrain
• Wing dihedral

Vection illusion

• movement in peripheral vision
• Hovering over water Or long grasses
• waterfall illusion
• formation flying

Question 15

What stages of flight are illusion more likely to occur

Answer 15

Approach and landing
Mid-air collision
High altitude
Over water
High speed, low level
flying at nigh

Question 16

Illusion with slope on runway

Answer 16

Upsloping runway = short, Pilot feels height and corrects low
Downsloping runway = long, pilot feels low and corrects high

Question 17

Visual challenges at low level and high speed

Answer 17

Blur zone
Overwhelming streaming cues
Limited time to perceive and react
Vibration degrades vision
Weather may limit visual cues
Terrain shadowing
Identifying ground feature
Power lines
Bird strike

Question 18

Visual challenges of high altitude flight

Answer 18

Empty field myopia
Horizon illusion
Glare
Different illumination cues 
ultraviolet

Question 19

Challenges of over water flight

Answer 19

Poor altitude cues
Poor motion streamling cues
Horizon definition
Glare off water
Empty field myopia
Landing over water

Question 20

Visual challenges of night flying

Answer 20

Low light - rod vision
Degraded visual cues
Physiological Night blind spot
Empty field myopia
Fatigue
Mild hypoxia
Illusion
Dark adaptation time
NVGs

Question 21

Vision illusions at night

Answer 21

Black hole approach
Autokinesis
Ground light confusion
Misperceptions on landing - high flare

Question 22

What is later refractive disorder

Answer 22

Latent myopia unmasked at night
Pupillary dilated ion - large aperture
Chromatic aberration cues lost

Question 23

How to maximise visual performance at night

Answer 23

Pre flight

• good nutrition
• Avoid bright light during the day
• Look off - centre
• clean visors and windscreens
• Correct refractive errors

During flight

• dark adaptation
• don’t look at bright lights
• Scanning technique
• Oxygen

Question 24

Characteristic of optimal eyewear

Answer 24

Frames: comfortable, robust, thin arms, maximum FOV, large lens area, compatible with all ALSE
Lens: CR39, large, focal distance for cockpit, large bifocal segment, impact resistance, anti-up

Question 25

Limitations and approval for corrective eye wear

Answer 25

Progressive lenses are allow
Limitation with frames and lenses types
Need to be CR39, Coated lenses, not polarised
Needs functional assessment
Contact lenses - meet standards and trial 7 days. Not authorised during field deployments or dust environment
Refractive surgery: PRK, LASEK, LASIK only. TMUSS 6 weeks and strict follow up for 12 months post op. Needs AVMO and command approval.

Question 26

Over long distances, the brain uses which cue to judge distance and depth
A. Stereopsis
B. Convergence
C. Accommodation
D. Aerial perspective

Answer 26

D. Aerial perspective

Monocular is over 200m

Question 27

The see and avoid principle is limited due too what?

Answer 27

Constant relative bearing no a collusion path
Closing speed exceeds visual perception time
Threshold of acuity
Target contrast
Degraded visual performance

Fix it with proper scan pattern

Question 28

What are the restriction with contact lenses

Answer 28

Must meet selection criteria and be approved
Extended wear, soft and disposable CLs preferred
Ground trial of 7 days with at least 8 hours per day comfortably use
Hygiene procedure and duration of wear in place
Not authorised during field deployment or dusty environments