vision

Question 1

what is sight

Answer 1

perception of objects in environment by means of the light they emit or reflect

Question 2

name the accessory structures for vison

Answer 2

Eyebrows
Eyelids
Conjunctiva
Lacrimal apparatus
Six Extrinsic eye muscles

Question 3

what is a sty

Answer 3

Inflamed ciliary gland of eyelash

Question 4

what is a meibomian cyst

Answer 4

Infected oil-secreting tarsal glands

Question 5

what is the Conjunctiva

Answer 5

Transparent mucous membrane, vascular

Question 6

what is the Lacrimal apparatus

Answer 6

Gland & duct drain tears to nasal cavity

Tears contain bactericidal lysozyme

Question 7

name the lacrimal structures

Answer 7

lacrimal gland (just above eye lid)
and
nasolacrimal canal (just a bit above hole of nose)

Question 8

what do the Lacrimal gland & Nasolacrimal duct do

Answer 8

drain tears to the nasal cavity

Question 9

how many extrinsic muscles of the eye are there

Answer 9

6

Question 10

name the extrinsic muscles and the eye movements that they carry out

Answer 10

Superior rectus muscle:
- Upward, slightly outward

Inferior rectus muscle:
- Downward, slightly inward

Medial rectus muscle:
- Inward, toward the nose

Lateral rectus muscle:
Outward, away from the nose

Superior oblique muscle:
- Inward, downward

Inferior oblique muscle:
Outward, upward

Question 11

describe the anatomy of the eye

Answer 11

Sphere with 3 principal components:
- Tunics: 3 layers that form wall
- Optical apparatus: admits & focuses light
- Neural apparatus: retina + optic nerve

Retina part of 1 & 3
Cornea part of 1 & 2

Question 12

name the 3 tunics

Answer 12

Tunica fibrosa
Tunica vasculosa
Tunica interna

Question 13

explain the Tunica fibrosa

Answer 13

sclera (white of eye) & cornea (transparent region; admits light into eye)

Question 14

explain the Tunica vasculosa

Answer 14

uvea, under fibrosa (=choroid, ciliary body & iris)

Choroid = highly vascular, deeply pigmented layer behind retina

Ciliary body = thick extension of choroid, forming muscular ring around lens; supports iris & lens & secretes aqueous humour

Amount of melanin determines eye colour

Question 15

explain the Tunica interna

Answer 15

retina

Question 16

name the 3 layers of the eye (its outer surface surrounding the eye)

Answer 16

sclera (the most outer layer)
choroid
retina (most inner later of the eye layers)

Question 17

what are the transparent elements of the eye and what are for

Answer 17

to admit/bend/focus light

• Cornea
• Aqueous humour
• Lens (if cloudy = cataract)
• Vitreous body = transparent jelly

Question 18

where is the Aqueous Humor produced

Answer 18

by ciliary body

Question 19

explain the Aqueous Humor in terms of what it flows through and what reabsorbs it

Answer 19

Flows through pupil into anterior chamber

Reabsorbed by ring-like blood vessel
- canal of Schlemm (= scleral venous sinus)

If reabsorption < secretion, pressure
- glaucoma

Question 20

explain the structure of Optic Disc in Glaucoma

Answer 20

The pink rim of disc contains nerve fibers.

The white cup (in middle) is a pit with no nerve fibers.

As glaucoma advances, the cup enlarges until it occupies most of the disc area.

Question 21

what cup to disc ratio indicated glaucoma

Answer 21

If cup to disc ratio >0.6, indicates glaucoma.

Question 22

what shape is the lens of the eye

Answer 22

curved structure
‘Ellipsoid’ in shape, 10 mm across x 4 mm front to back

Question 23

what is the crystalline lens

Answer 23

a clear disk behind the iris

flexible and changes shape to help you see objects at varying distances.

Question 24

what does the lens of the eye do

Answer 24

Bends light and focuses it for the retina to help you see images clearly.

Question 25

what happens to the eye lens as you age

Answer 25

the lens may become weaker or damaged.

Question 26

what is cataracts

Answer 26

changes in proteins (crystallins), clumping. cloudiness vision through pupil

Question 27

explain the retina

Answer 27

Innermost layer; thin, transparent membrane 2 attachment points (optic disc & ora serrata [scalloped anterior margin]) Examine with ophthalmoscope - Look for signs of hypertension, diabetes, atherosclerosis etc.

Question 28

explain macula lutea

Answer 28

directly posterior to centre of lens, with central fovea centralis (mostly finely detailed images); no rods, only cones; highest concentration of cones

Question 29

explain the optic disc

Answer 29

where all nerves & blood vessels pass Creates ‘blind spot’ in vision

Question 30

what is Proliferative Diabetic Retinopathy (PDR)

Answer 30

when Irregular new blood vessels form from the retina this can cause black patches in vision

Question 31

explain how an image is formed

Answer 31

Pupil admits light: Diameter controlled by iris: - Pupillary constrictor = concentric circles of SMC to narrow pupil - Pupillary dilator = spokelike myoepithelial cells, widen pupil Light is bent (refracted): - By curvature of cornea towards centre of retina - Refractive Index = measure of light retarded; lens merely fine tunes The Near Response: - Adjustment to close range vision

Question 32

what does changing the curvature of the lens do

Answer 32

Light from a single point of a distant object and light from a single point of a near object being brought to a focus by this changing in curvature

Question 33

what are the 3 processes involved to focus a near response image on retina

Answer 33

Convergence of Eyes: - If problem, double vision Constriction of Pupil: - Screens out peripheral light rays that cannot be refracted well Accomodation of lens: - Change in curvature to focus

Question 34

what is near response

Answer 34

the closest an object can still be in focus.

Question 35

name some common defects of image formation

Answer 35

Hyperopia Myopia

Question 36

what is Hyperopia

Answer 36

Image (focal plane) behind retina Correct with convex lens Hyperopia = “Far sighted” Image too far, behind eyeball Can see far objects correctedwith convex lense

Question 37

what is Myopia

Answer 37

Image within vitreous Correct with concave lens Myopia = “short-sighted” Image falls ‘short’ within eyeball Can see near/short

Question 38

explain Sensory Transduction in Retina

Answer 38

Conversion of light energy into action potentials occurs within retina Consider: - Cellular layout - Pigments that absorb light - What happens when light is absorbed

Question 39

how many layer are there of the retina

Answer 39

5

Question 40

name the 5 cellular layers of the retina

Answer 40

Pigment cell layer – retinal (RPE) absorb light (melanin) & reduce light scatter Photoreceptor layer - RODS – periphery, night - CONES – centre of eyeball, day & colour Bipolar layer Ganglion layer - largest neurons of retina Nerve Fibre layer

Question 41

what are the visual pigments in rods

Answer 41

RHODOPSIN (retinal+opsin) (retinal is a pigment; opsin is a protein)

Question 42

what are the visual pigments in cones

Answer 42

PHOTOPSIN (retinal+~opsin) (retinal is a pigment; opsin is a protein)

Question 43

what is retinol

Answer 43

a pigment

Question 44

what is opsin

Answer 44

a protein

Question 45

whats the shape of rods

Answer 45

long and thin

Question 46

whats the shape of cones

Answer 46

short and wide

Question 47

what is photochemical reaction

Answer 47

Cyclical process, same in rods & cones cis-retinal (bent) absorbs photon of light, and with the requirement of ATP, it becomes trans-retinal (straight). which creates a nerve signal trans-retinal can become cis-retinal by the dissociation from opsin

Question 48

Colour Vision is based upon what

Answer 48

Based on 3 types of cones: Blue Green Red

Question 49

Perception of colour is based on what

Answer 49

on mixture of nerve signals from above

Question 50

what do people with Dichromats do

Answer 50

confuse the colours of red and green

Question 51

explain the visual pathway

Answer 51

the route of the visual image, from the retina through the optic nerve, crossing over at the optic chiasma, where the left field of vision is processed by the right side (& vice versa), moving along the optic tract to the thalamus, and on to the visual cortex (in the occipital lobe), where the brain interprets what is seen.