Physiology Of Vision Flashcards
Importance of vision in Aviation
80% of spatial orientation cues Visual scanning Collision avoidance Depth and distance perception Situational awareness
What threats degrade visual performance in military aviation?
Physiological threats
- G force, fatigue, hypoxia, medical conditions, medication
Physical threats
- Lasers, bird strike, MDC splatter, wind blast, glare, UV radiation, ionising radiation, NVGs
Role of cones in focal vision and its weaknesses
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
Role of rods in peripheral vision and its weakness
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
Types of depth perceptions and their cues
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
Physiological limitation of visual performance
Focal traps Empty field myopia Threshold for acuity Saccadic vision Cues of dept perception Anatomical blind spot Physiological blind spot Perception time
Explain Focal traps
Chip on windscreen
Focus on the foreground
Functionally myopic
Define empty field myopia
Rest position of gaze is 1-2 meter
Functional myopia, can’t see distance
Threshold of acuity
6/60 minimal distance
Saccadic eye movement
Rapid flicking movement of eyes
Blurs retinal image
Targets may not be perceived
Limitation of depth perception
Binocular cues - limited by distance
Monocular - misperceptions based on learned cues and expection
Illusions from focal or peripheral vision
Focal - Absent or inadequate visual cues, Errors of top down processing
Peripheral - False horizons, illusion of movement (vection)
What are illusions from central visual processing
Brown out
White out
Terrain shadows and illumination
Night illusion
Illusions from peripheral vision
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
What stages of flight are illusion more likely to occur
Approach and landing Mid-air collision High altitude Over water High speed, low level flying at nigh
Illusion with slope on runway
Upsloping runway = short, Pilot feels height and corrects low
Downsloping runway = long, pilot feels low and corrects high
Visual challenges at low level and high speed
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
Visual challenges of high altitude flight
Empty field myopia Horizon illusion Glare Different illumination cues ultraviolet
Challenges of over water flight
Poor altitude cues Poor motion streamling cues Horizon definition Glare off water Empty field myopia Landing over water
Visual challenges of night flying
Low light - rod vision Degraded visual cues Physiological Night blind spot Empty field myopia Fatigue Mild hypoxia Illusion Dark adaptation time NVGs
Vision illusions at night
Black hole approach
Autokinesis
Ground light confusion
Misperceptions on landing - high flare
What is later refractive disorder
Latent myopia unmasked at night
Pupillary dilated ion - large aperture
Chromatic aberration cues lost
How to maximise visual performance at night
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
Characteristic of optimal eyewear
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
