Neuro-visual System

Question 1

what is the limbus

Answer 1

border between cornea and sclera

Question 2

what are the 3 layers of the eye and brief functions

Answer 2

sclera= hard and opaque

choroid= pigmented and vascular coat

retina= neurosensory tissue

Question 3

what does the uvea contain and it’s function

Answer 3

vascular coat
iris, ciliary body and choroid

-one part affects the other (in disease)

Question 4

retina function

Answer 4

captures light rays- light impulses sent to brain via optic nerve

Question 5

macula
where is it to optic nerve?
function?
what is at the centre?

Answer 5

-temporal to optic nerve
-detailed central vision
-fovea- give detail ventral vision ie. reading

Question 6

what is a blind spot

Answer 6

where optic nerve meets retina- no light sensitive cells.

Question 7

optic nerve meeting retina- what is it called

Answer 7

optic disc

Question 8

what does the central vision involve-
which photoreceptor dominates?
how to assess
what happens when foveal vision is lost

Answer 8

detail/colour vision
-cone receptor
-visual acuity assessment
foveal lost= poor visual acuity

Question 9

what does the peripheral vision involve-
how to assess ?
what happens when visual field is lost?

Answer 9

movement and night vision
-visual field assessment
-unable to navigate- may need white stick even with perfect visual acuity

Question 10

Retinal structure what is in the
outer layer
middle layer
inner layer
- and what each does

Answer 10

outer layer
- photoreceptors-1st order neuron
-detect light

middle layer
- bipolar cells (2nd ON)
-local signal processing

inner layer
-retinal ganglion cell (3rd ON)
-transmission of signal from eye to brain

Question 11

photoreceptor- what is rods

Answer 11

-more sensitive to light
-slow response to light
-night vision
-most abundant

Question 12

photoreceptor- what is cones

Answer 12

less sensitive to light but faster response
-day light fine (+colour) vision

Question 13

what is emmetropia

Answer 13

adequate correlation between axial length and refractive power

-parallel light rays fall on retina

Question 14

what is it called when there is a refractive error-
mismatch between axial length and refractive power- parallel light doesn’t fall on retina?- overall terminology

Answer 14

ametropia

Question 15

what is myopia and causes

Answer 15

Parallel rays converge at focal point anterior to retina.

Causes
-excessive long globe (axial myopia)-common
-excessive refractive power (refractive myopia)

Question 16

myopia symptoms

Answer 16

Blurred distance vision
Squinting
Headache

Question 17

what is hyperopia and causes

Answer 17

Parallel rays converge at a focal point posterior to the retina

Causes
-excessive short globe (axial hyperopia) :common
-insufficient refractive power (refractive hyperopia)

Question 18

hyperopia symptoms

Answer 18

blurring at close distance
eye pain/headache

Question 19

what is the near response triad

Answer 19

-pupillary miosis- sphincter pupillae=increase field depth

-convergence -medial recti

-accommodation - circular ciliary muscle= increase lens refractive power

all contracts

Question 20

presbyopia what is it? age of onset?

how is it corrected ?

Answer 20

-natural loss of accommodation.
-40y.o +
-corrected by reading glasses (convex)- increase refractive power.

Question 21

Visual Pathway Anatomy

Answer 21

1. eye
2. optic nerve
3. optic chiasm
4. optic tract
5. lateral geniculate nucleus (thalamus- synapse)
6. optic radiation=4th order neuron
7. primary visual cortex

Question 22

common causes of homonymous hemianopia

Answer 22

stroke

Question 23

why is there macular sparing in some homonymous hemianopia

Answer 23

damage to primary visual cortex
-ie stroke
-macula receives dual blood supply from posterior cerebral arteries from both sides

Question 24

in light- pupil constrict-> which nerve is it mediated by and which muscle contract

Answer 24

parasympathetic nerve (CN III)

contract circular muscle

Question 25

in dark- pupil dilatation-which nerve is it mediated by and cause which muscle to contract

Answer 25

sympathetic nerve

contract radial muscle

Question 26

explain the pupillary reflex steps

Answer 26

afferent-
1. pupil-specific ganglion cells exit optic tract (before LGN)
2. synapse at brainstem pretectal nucleus
3. synapse at Edinger-Westphal Nuclei on both sides in brainstem

efferent-
4. Edinger-Westphal nucleus–> oculomotor nerve efferent
5. synapse at ciliary ganglion
6. short posterior ciliary nerve –> pupillary sphincter

Question 27

what is it called when pupil constrict from direct light stimulation vs constriction of pupil in the other eye

Answer 27

direct vs consensual pupillary reflex

Question 28

what is the swinging torch test for (hint- damage to afferent pathway is usually incomplete/relative). How to do the test?

Answer 28

relative afferent pupillary defect
-alternating stimulation of right and left eye with light

Question 29

results of swinging torch test if
left=undamaged
right=damaged (relative-afferent pathway)

Answer 29

-both pupils constrict when light swings to left undamaged side

-both pupils paradoxically dilate when light swings to right damaged side =positive sign

Question 30

what nerve innervates lateral rectus and superior oblique

Answer 30

lateral rectus= CN 6- abducens

superior oblique= CN 4- trochlear