Flashcards in Visual defects Deck (68)
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1
Pupil
Opening that allows light to enter the eye, seems dark because of the light absorbing pigment epithelium in retina
2
Iris
Colour, 2 muscles - may vary in size
3
Cornea
Glassy transparent external surface of eye, lacks blood vessels, nourished by aqueous humour, continuous with sclera
4
Extraocular muscles
3 pairs
5
Conjuctiva
Membrane that folds back from inside of eyes and attaches to sclera
6
Optic nerve
Carries axons from retina > brain
7
Lens
Transparent structure suspended by ligaments (zonule fibres), attached to ciliary muscles control shape of lens
8
Vitreous humour
Viscous jellylike substance, between lens and retina, keeps eye spherical
9
Retina
Where light is transformed into neural activity (part of CNS)
10
Fovea
Highest visual acuity, light can reach photoreceptors directly
11
Refraction
Bending of light rays,occurs when light passes from one transparent medium (air) to another (cornea), bends towards a line that is perpendicular to the border betwen media
12
As light passes through the cornea
Light rays that strike curved surface of cornea bend so they converge on back of eye > retina
13
Closer images and refraction
Require greater refractive power to bring them into focus, occurs by lens changing shape (accommodation)
14
Lens accomodation
Rounding of lens increases curvature of lens surface and increases refractive power, ability to accomodate lens changes with age
15
Ciliary muscles
Allow lens to change shape, contraction relieves tension of zonule fibres allowing it to become rounder
16
Emmetropic eye
Normal - focuses parallel light rays on the retina without need for accommodation
17
Hyperopia
Farsightedness
18
Farsightedness/hyperopia
Eye too short, light focuses behind retina, convex lens used for refraction to allow near objects to be brought to focus
19
Myopia
Nearsightedness
20
Nearsightedness/myopia
Eyeball too long, parallel light rays converge before retina, concave lens refraction to allow distant objects to be brought into focus
21
Photorefractive keractectomy
Corrective laser surgery, uses laser to reshape the cornea and increase/decrease amount of refraction possible
22
Macula
Central vision
23
Fovea
Central/thinner region of retina
24
Optic disc
Origin of blood vessels, where optic nerve axons exit, blind spot
25
The retina
- Light is focused by cornea and lens > vitreous humour > retina
- Pigment epithelium (behind retina), filed with melanin - absorbs light not absorbed by retina
- Light passes through all retinal cells > photoreceptors
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Photoreceptors - absorption occurs in
Outer segments of photoreceptors (stack of membranous disks - light sensitive photopigments)
27
Photoreceptors transduce
Light energy > changes in membrane potential
28
Cones
Lower sensitivity, day light, colour, fast response, high acuity, concentrated in fovea, trichromatic
29
Rods
High sensitivity, more photopigment, high amplication, slower response, low acuity, not in fovea, lots of them connected to less neurones than cones
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