Optic Neŕve

Question 1

Which Cranial nerve is it? Where does it start and end?

Answer 1

2
From retina to optic chiasm

Question 2

How many sections and name them

Answer 2

1. Intra-ocular (1mm) visible
2. Intra- orbital (25 to 30mm)
3. Intra-canalicular (4-10mm)
4. Intra-cranial (10mm)

Question 3

How long is ON and how many nerve fibres?

Answer 3

50mm long
1 million nerve fibres
Mostly afferent

Question 4

Optic disk vs optic head. What is the ONH.

Answer 4

Disk- 2D view/flat/seen with opthamolscopy
Head-3D view/seen with OCT
ONH- collection and exit point for axons of retinal gang cells

Question 5

Lamina cribosa?

Answer 5

Perforations on sclera
Mesh of collagen fibres
Pathway for RNF to exit eye
Structural support to ONH if IOP increases
Increased visibility of LC ~glaucoma/shallow cup

Question 6

Optic cup?

Answer 6

Nerves bend 90° to enter ON
Peripheral fibres=deeper = longest distance to ON

Question 7

Distribution of nerve fibres in optic disc?

Answer 7

Pattern is TOPOGRAPHICAL
MACULAR fibres- enter TEMPORALLY
Mac fibres form PAPILLOMACULAR bundle
Nasal fibres - enter nasally
Superior and inferior fibres bend round macula
Individual fibres X cross horizontal raphe(midline)

Question 8

Blind spot?

Answer 8

X photoreceptor at optic head
X aware of blind spot location bz input from each eye overlap and compensate (~15°temporal to fixation)

Question 9

Bld supply to intra-ocular?

Question 10

3 types of mater and their structure?

Answer 10

Protective layers around ON
Dua- toughest
arachnoid- highly vascular
pia- thin
Only start in intra- orbital layer

Question 11

Myelination?

Answer 11

Insulation so X short circuit
Starts after ONH so nerves in return should NOT be myelinated
If seen in ONH, appears as fuffy white patch - follows nerve pattern

Question 12

Glial cells structure and function

Answer 12

Around fibre axons
Homeo and structural support
3 types, varying density: astrocytes , Oligodendrocytes, NG2

Question 13

Blood supply in ON Head and choroid

Answer 13

By short posterior cil artery
Low bld supply= paler ONH (pallor)

Question 14

Braches of Bld vessels?

Answer 14

Internal Carotid Artery》Opthalmic artery》Central Ret Art & Short Posterior Cil A

Question 15

Blood supply to retina?

Answer 15

Central Retinal artery

Question 16

Which open space does ON pass thru at back of orbit?

Answer 16

Optic canal

Question 17

What happens to protective layers in cranium?

Answer 17

Dura and arachnoid disappear

Question 18

Optic disk parameters

Answer 18

Location: 10° nasal & 2.5 degrees superior to fovea
Size: 7°vertical x 5°horizontal
Shape: oval, slight tilt

Question 19

How to estimate depth of ON with opthamolscopy?

Answer 19

Change in focus
Higher changer=deeper cup

Question 20

Optic disc?

Answer 20

3 items: cup,NNR, Margin
CD ratio: less than 1
Fewer nerve fibres =bigger cup
Same # of fibres in healthy eye despite disc size
Volk Super 66= definite size of disc(X mag)

Question 21

Estimate Optic disc size

Answer 21

Knowing aperture size with direct opthamolscope
Colour change
Bld vessel bending

Question 22

NRR?

Answer 22

Neuroretinal rim
Colour from bld vessels
Pallor from damage to bld supply/nerve fibre loss
Width : ISNT
Vertical CD ratio more inportamt- changes during glaucoma