Visual defects Flashcards Preview

CM Clinical Symposia > Visual defects > Flashcards

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

26

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

30

Rhodoposin

Pigment in rods (receptor protein - opsin)