Eye and vision

Question 1

parts of the eye

Answer 1

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

Question 2

accommodation of the lens

Answer 2

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

Question 3

eye movement

Answer 3

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

Question 4

2 types of photoreceptors are?

Answer 4

cones & rods

Question 5

cones

Answer 5

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

Question 6

rods

Answer 6

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

Question 7

rods and cones Adaption

Answer 7

10 secs for rods and cones to adapt to bright light

adapting to dark- rods take 30 min , cones take 7 min

Question 8

visual acuity

Answer 8

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:
smoking
alcohol
hypoxia
some medications

Question 9

visual field

Answer 9

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

Question 10

depth perception

Answer 10

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

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

Question 11

binocular depth cues:

Answer 11

inward turning/ converging eyes when object close

stereoscopic vision: differing images from each eye, brain puts together and gathers perception

Question 12

monocular perception cues

Answer 12

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

Question 13

blind spot

Answer 13

where optic nerve leaves back of the eye

no cones and rods so blind spot

Question 14

empty field myopia

Answer 14

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

Question 15

scanning technique

Answer 15

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

Question 16

myopia

Answer 16

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

Question 17

hypermetropia

Answer 17

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

Question 18

Presbyopia

Answer 18

develops as get older

form of hypermetropia as ciliary muscles become less flexible

Question 19

Astigmatism

Answer 19

mis shapen cornea, abnormalities in lens

cured by lenses or surgery

Question 20

cataracts

Answer 20

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

Question 21

glaucoma

Answer 21

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

Question 22

glaucoma symptoms

Answer 22

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

Question 23

colour vision deficiency

Answer 23

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

Question 24

flash blindness

Answer 24

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

Question 25

corrective lenses requirements

Answer 25

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

Question 26

contact lenses

Answer 26

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

Question 27

sunglasses

Answer 27

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

Question 28

sunglasses: photo chromatic lenses

Answer 28

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

Question 29

sunglasses: polarised

Answer 29

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