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Flashcards in Eye and vision Deck (29)
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parts of the eye

sclera- white bit
cornea- 70-80% of focusing
aqueous humour- keeps shape
iris- control size of pupil
pupil- hole
lens- 20-30% focusing- changes shape to focus- called accommodation
ciliary muscles- change shape of lens
retina- layer at back with photosensitive receptors
fovea- central part of retina, clearest vision
vitreous humour- keeps shape
optical nerve - connects eye to brain


accommodation of the lens

thickens to focus close- convex
flattens to focus further away- concave
age and fatigue affect ability to change shape of the lens
dioptres- reactive power of the lens, Avg 16-30D


eye movement

6 muscles
extraocular muscles
series of jerks called saccade
saccade period- 1/3 of a second including a period of rest


2 types of photoreceptors are?

cones & rods



bright light conditions, photopic vision
colour sensitive(RGB rods)
cover area approx 1deg wide, concentrated at fovea where there's 150 per mm
used for central vision
enables details, colours & movement to be seen
depicting alphanumeric information is limited to fovea and cones



low light, night vision, scotopic vision
not sensitive to colour, black and white
contain rhodopsin which is destroyed by bleaching on exposure to light
used for peripheral & night vision( very sensitive to movement but not in detail)
spread over larger area- max number about 10deg from fovea


rods and cones Adaption

10 secs for rods and cones to adapt to bright light
adapting to dark- rods take 30 min , cones take 7 min


visual acuity

measure of central vision, ie from fovea
avg vision is 20/20
angle at which light hits fovea or distance away from fovea it hits affects vision
hits 5deg away from fovea: acuity halves
hits 25deg away from fovea: acuity 1/10th

factors affecting:
some medications


visual field

each eye can see:
up and down 150deg
left and right 120 deg
binocular vision- 60deg overlap
visual field made up of binocular and peripheral vision


depth perception

ability to detect distance of an object
need both eyes for best perception

monocular perception:1 eye
parallax error
depth perception not as good


binocular depth cues:

inward turning/ converging eyes when object close
stereoscopic vision: differing images from each eye, brain puts together and gathers perception


monocular perception cues

1 eye
parallax error
depth perception not as good

relative size
elevation/ relative height
absolute or actual size
texture gradient
motion parallax
arial/atmospheric perspective
linear perspective
overlap/ interposition
shading and lighting


blind spot

where optic nerve leaves back of the eye
no cones and rods so blind spot


empty field myopia

if eye not stimulated(e.g. clear sky) will focus on point 1-3m away


scanning technique

split horizon into 10° segments
start at first segment and scan for 2 seconds and move to next segment and so on
at night look to the side of objects as using rods



short sighted
image short of retina
blurred image on retina
need diverging/ concave lenses



long sighted
image falling/ forms behind retina
converging/ convex lens



develops as get older
form of hypermetropia as ciliary muscles become less flexible



mis shapen cornea, abnormalities in lens
cured by lenses or surgery



opacity/ clouding of the lens
develops due to ageing
cured by surgery



caused by pressure of liquid in the eye
untreated can lead to blindness
cured by drops or surgery
insidious onset of concealed progression
affects peripheral vision first


glaucoma symptoms

acute pain in eye
blurred vision
sensitivity to high levels of light
visual field deterioration
red discolouration of eye


colour vision deficiency

1 or 2 types of cones not working = deficiency
all 3 types not working = blindness
doesn't affect visual acuity
can occur as we get older
occurs in 7% of men, 0.1% of women
may still be able to fly


flash blindness

flashes of light at night can cause temporary blindness
lightning, lasers
damages Rhodopsin(visual purple)
may be an idea to increase lighting on flight deck so flashes have less effect, or wear sunglasses


corrective lenses requirements

have a spare pair
spare can be prescription sunglasses
night flying- best that you have a spare pair of clear glasses


contact lenses

can dry out which can damage cornea
can become dislodged by ribbing eye, G-forces or accidental break
bubbles can form if decompression occurs
bifocal prohibited
if cleared for use must have spare pair of ordinary specs



protects against damaging UV
tint should be neutral colour
no darker than 80% absorption
graduated tint useful
frames should be well fitting & large enough to allow sufficient protection


sunglasses: photo chromatic lenses

react with UV by darkening
cockpit designed to block out
these lenses will not work effectively on flight deck
use of these sunglasses discouraged


sunglasses: polarised

reduce amount of light passing through by selective filtering
cause distortion patterns from laminated windshields
cloud appearance and reduce ground reflections useful for VFR
use of these sunglasses prohibited