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Flashcards in Vision + Visual Field Deck (39)
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1

What happens when light enters eye

Travels through all layers of retina to reach rod and cones (photoreceptor)
Transduction occurs to convert light -> chemical
Travels back and synapse at nerve fibre layer
Joint optic nerve to generate AP (photoconduction)

2

What is fovea centralis

Area packed with cone cells for max visual acuity
Located within the macula
High concentration of cone cells
Exposed so don't have to pass through all layers of retina
Eyes will move to focus on this

3

What is the macula

Small area at centre of retina for central field of vision
Contains highest conc of cone cells

4

How do rod and cone cells work in the dark

At rest
Depolarised by open Na / Ca) channel

5

What do rod and cone cells do different

Different visual pigment
Rhodopsin pigment in rods = low light
Opsin in cones = daylight / colour

6

Colour blindness

Defect in cone cells or pathway to brain

7

What happens when light enters aye

Changes vit A in pigment to all-trans-retinal (ActivateD)
Molecule can't fit into rod / cone
Splits = bleaching and activation of visual pigment (rhodopsin / opsin)
Picked up and changed back to original but only if have diet vitamins A

8

What is activated rhodopsin

No vit A present 11'cis-retinal

9

What happens when activated

Causes channels to close
Hyperpolarisation
AP forms and travels to optic nerve in nerve fibre layer

10

What happens if vit A deficiency

Can't see in the dark
Unhealthy conjunctival and cornea
Bitots spots (triangular silver foam) in conjunctiva
Ulceration
Corneal melting + opacification

11

What is refraction

Bending of light rays to form a sharp image on retina when changing from one optic medium to another

12

What are main mediums

Cornea + lens
AH / VH = refract slightly

13

When do errors occur

If mismatch in bending

14

What happens if object close

Eye needs to bend more to focus
Lens becomes thicker

15

If object >6m

Light is parallel

16

If <6m

Divergent rays so bend

17

What is convex

Makes light converge (bend in)

18

What is concave

Makes light diverge (bend away)

19

What is accommodation

Bending light to focus on far off or near objects

20

What happens

Lens thicker to focus on close object
Pupil constrict for sharp focus
Eyes converge - MR (III)

21

What are intrinsic ocular muscles and nerve

Pupillary constrictor - para III - Ach
Pupillaey dilator - sympathetic - NA

22

What happens if increased light and what is the mechanism

Pupil constrict
Light on retina
Travels to optic nerve -> chiasma -> tract
Do not go to LGB
Go to mibrain and synapse on III on both sides

23

What happens if decrease

Pupil dilates

24

What are extrinsic ocular muscles

Superior rectus
Inferior rectus
Lateral rectus - CN6
Medial rectus
Superior oblique - CN4
Inferior oblique
All other CN3

25

LOOK AT EYE

OK

26

Where is L half of visual field seen

R side of retina

27

What is the pathway of visual field

Optic nerve -> optic chiasma
Medial fibres (nasal) cross to opposite side
Lateral stay the same
Travel in optic tract and synapse in LGB of thalamus
Optic radiation travels through internal capsule
Goes to visual cortex in occipital lobe

28

What does process at chiasma mean

Optic tract contains fibres from lateral half of ipsilateral and medial from contralateral
so ALL fibres from opposite half of visual field = optic tract
L visual field = R optic tract

29

What does L side of brain receive

L visual field of both eyes

30

What happens if R optic nerve damage

No vision in R eye
Direct reflex is absent but indirect will remain intact