Vision Flashcards
Anatomy of eye
*KNOW WHERE THEY ARE
Cornea - very front protective layer
Iris - colored portion of eye, opens and closes
Pupil - black part of eye
Ciliary muscles/fibers - close and open iris
Crystalline lens - lets light into eye, refracts it onto retina
Retina - back inner of eye, light is refracted on, Rods and Cons interpret
Optic nerve - sends data
Photoreceptor cells
On the retina
(Fovea - packed with cone cells, bump on rear of eye)
Cone cells - used in bright light, IDENTIFIES COLOR, sharp visual acuity and color sense, 7 million in fovea and parafoveal regions, 1:1 RATIO OF CONE CELLS TO NERVE CELLS
Rod cells - used in low light, can identify outlines/silhouettes, poor color sense and visual acuity, 120 million rod cells, 10:1 to 10000:1 ratio of rod cells to neuron cells. Produces Rhodopsin (visual purple)
Fovea centralis
Central vision , has no rod cells (produces night blind spot), the little bump on the retina near the optic nerve
Day blind spot
One of the retinal blind spots (1 of 2)
Related to the position of the optic (nerve) disk on the retina
Located 15 degrees from fovea
No photoreceptor cells (rods or cons)
*Encompasses 5.5 to 7.5 degrees of visual field
Compensate with binocular vision
Night blind spot
One of the retinal blind spots (1 of 2)
Located in central viewing axis (fovea)
*Absence of rod cells in fovea
Inability of cone cell function
*Encompasses an area of 5-10 degrees of central, visual field
Viewer must SCAN to compensate
Visual deficiencies
*Astigmatism - due to unequal curve of cornea, can ot focus on horizontal and vertical objects simultaneously
Glare disability - inability to detect objects against varying shades or backgrounds-related to contrast
- Myopia - nearsightedness
- Hyperopia - farsightedness
- Presbyopia - (aging) hardening of lenses, cataracts
Allowable refractive surgeries
PRK - Photorefractive Keratectomy (slowest return, but least susceptible to flap issues
LASIK - Laser in Situ Keratectomy (most common)
LASEK - Laser Subepithelial Keratectomy (carving of corneas to big for LASIK)
Types of vison
*PMS
Photopic - daylight/bright light, central vision, visual acuity 20/20
Mesopic - dawn/dusk, full moonlight; parafoveal region (rods and cons), decrease acuity and color sense (increase scanning)
Scotopic Vision - night vision (partial moon/stars), peripheral vision only (rods), silhouette recognition, loss of color perception
Binocular cues
Valuable only when the object is close
Each eye has a slightly different view
Operates subconsciously
Little value in flight enviornment
Visual cues
Monocular cues - *GRAM
G) geometric perspective (LAV)
R) retinal image size (KITO)
A) aerial perspective (FLP)
M) motion parallax (*most common cue to depth perception)
Geometric Perspective (LAV)
Objects have different shapes when viewed at varying distances and altitudes (linear objects like rail lines seem to converge)
Retinal image size (KITO)
K) known size of objects
I) increasing or decreasing size of objects
T) terrestrial association
O) overlapping contours (position of convoy)
Aerial perspective (FLP)
An objects clarity and its shadow are perceived by the brain as cues for estimating distance
F) fading of colors and shades
L) loss of detail or texture
P) position of light and direction of shadow
Motion parallax
*Most important cue to depth perception (stationary objects, observer moving)
Rate depends on the relative distance of the object from the observer
Limitations of night vision
Depth perception (safe landings)
Visual acuity (obstacle identification)
Night blind spot
Dark adaptation (time factor)
Color perception
Night myopia (decreased color, visual acuity)
Visual cues
Depth perception
Mental projection of perceived object in space
Correlation of “real object” to projected visual space
Decreased light affects ability of depth perception
*Two most important monocular factors - motion parallax and retinal image size
Visual acuity
How well you can see in daytime (20/20), is not how you see at night (legally blind status at night)
Night blind spot
At 3ft can miss a wrench, at 3,000ft can miss commercial aircraft (need to visually scan - use peripheral vision)
Dark adaptation
*average time required is 30-45 minutes
Red lens van help start dark adaptation
Exposure to intense sunlight, glare for 2-5 hours will increase time for dark adaptation for up to 5 hours
After full dark adaptation, 3-5 min of re-adaptation needed after exposure to brief bright light.
Vitamin A required for production of Rhodopsin
Color perception
Scotopic vision degrades primary color perception
Shades of black, gray, and white
Other colors perceived if light intensity increases
Night myopia
Blue wavelength light causes night myopia
- image sharpness decreases as pupil diameter increases
- mild refractive error factors combined, creates unacceptable blurred vision
- focusing mechanism of the eye may move toward a resting position (increases myopic state)
Visual illusions
ICCHAFFSS
I) induced motion C) confusion with ground lights C) crater illusion H) height-depth illusion (loss of visual cues) A) autokinesis** F) false horizon F) fascination/fixation S) structural illusion S) size distance illusion
Flight hazards
Solar glare
Bird strikes
L.A.S.E.E.Rs (light amplification by a stimulated emission of radiation) intense <1in diameter up to 2m at 2km
Nerve agents
Laser injuries
Lens - focuses and concentrates light rays entering eye
Concentration of energy inside eye is up to 100,000 times greater than light entering eye
Damage depends on laser type, exposure time, and distance (lesions on back of eye, flash blindness, impaired night vision, burns)
Laser protective measures
Passive - take cover, NVDs, squinting, protective goggles
Active - evasive action, scanning with one eye or monocular optics
Nerve agents
Threat in both day and night at low level flight
Consult FS immediately
Severity of miosis depends on agent concentration (direct or minute exposure will cause miosis - pupil constriction… severe miosis may last 48hrs, complete recovery could take 20 days)
Self-imposed stresses
DEATH
Drugs Exhaustion Alcohol Tobacco Hypoglycemia
