Eyes Flashcards
Visual System Composed Of
Eye
Optic Nerve
Visual Cortex
Visual System Composed Of
Eye
Optic Nerve
Visual Cortex
What keeps spherical shape of eye
Two fluids
- Aqueous Humour (front of eye)
- Vitreous humour (back of eye)
Supply nutrients to eye
Retina
Inner lining of the eye containing light sensitive cells (photoreceptors)
Lens
20/40% of focusing occurs here
Ciliary muscles change lens shape for accomodation
Ageing/fatigue impact ciliary muscles
Pupil
Hole in Iris
Contracts if too much light
Expands when not enough light
Cornea
Allows light to enter via the pupil
60/80% of focusing occurs here
O2 needed to keep moisture
Iris
Colour part of eye
Contract and expands to maintain constant level of light
BLIND SPOT
No Photoreceptors in optic nerve (optic disk)
Cones - primary vision role/where they are found
Primary vision in daylight
Colour vision (red, blue and green)
Key for central vision
Photopic (light seeing)
Central vision (visual acuity)
150,000 cones per mom
Found around fovea
Visual Acuity + figures away from fovea
Capacity of the eye to resolve detail
More photoreceptors greater the acuity
5 degree away from fovea = 1/2
25 degrees away = 1/10
Rods
Peripheral vision
Concentrated along retina
Black and white night vision
Scotopic vision
Sensitive to movement
Visual Field
Defined as the space which can be seen at any time by a stationery eye
120 degree to right
150 degrees up and down
Movement of eye to track and pursuit
6 extra ocular muscles
Saccade - sudden jerk
Attention - moving eye to place over fovea
Track - Smooth pursuit movements
Factors effecting visual acuity
Angular distance from fovea
Level of lighting (dark condition cones not functioning as well)
Distance of object
Age/disease
Hypoxia
Smoking
Medication
Short/long sightedness
Binocular vision
Gives stereoscopic vision (Judging close objects)
Estimate distance using two eyes effective to about 60m out
Non stereoscopic cues
Estimating the distance after being further out than binocular vision
Using:
Colour
Contrast
Size
Rate of movement
Monocular Vision
Loss of all depth perception of close objects
Does not affect depth perception far away
Struggle to catch a ball
Initial examination class 1 - seen as unfit
Revalidation - referred and then assessed for fitness
Dark adaptation
Cones = 7-9 minutes
Rods = 30 minutes
Lost if exposed to bright light
Light adaptation
Eyelids will close
Pupil to contract
10 seconds for photoreceptors to adapt
Flash Blindness
Sudden intense light causing degradation in vision temporarily
Can bleach photoreceptors and cause vision damage
Hazards of light at high alt
Blue and UV light (cumulative damage)
Good and bad quality’s of sunglasses
Dos:
High quality
Strong polycarbonate
Thin rims
Good optical qualities
Do Not:
Photochromic sunglasses
Polarised
Yellow tinted
Empty Field Myopia
Default to objects 1-2m ahead
Cloudless featureless sky
Regular eye movements overlapping sectors of about 10 degrees
Focus on objects at distant
Detecting objects in dark
Look at them slightly off centre
Scotopic vision used
Refractive Error Long Sightedness
(Hypermetropia)
Distance objects clear
Closed objects blurred
Convex len used to fix
Light focuses behind the retina
Refractive error - Short sightedness
Myopia
Close objects clear
Distant objects blurry
Corrected with concave lens
Light focuses in front of the retina
Astigmatism
Misshapen cornea/lens
Difficulty in resolving detail
Corrected by tailored lens
Rules for spectacles and contact lenses
Must have easy access spare at all times
Contact lenses can be worn for distant vision ONLY and no bi-focal lenses not permitted with contact lenses
Presbyopia
Longsightedness by age
Lens less flexible/elasticity of ciliary muscles reduces
Decrease in accomodation
Glaucoma
High pressure in the eye
Retinal blood supply cuts causing retinal cell death
Blindness
Sudden and painful - fine jet of pressurised air onto cornea measuring the deflection
What happens if you are in darkness for a long time and exposed to bright light
Dark adaptation and will hamper depth perception will take time to adapt to high brightness levels
Order of light passing through components in the human eye
Cornea/Iris/Pupil/Lens/Retina
Remember alphabetic order
What controls accomodation
Lens
What controls adaption
Pupil
Monocular cues for depth perception include
Obcuration
Texture
Atmospheric perspective
