Optic Nerve in Glaucoma Flashcards
(24 cards)
who is more likely to have a larger disc?
Based on gender and race
AA > caucasian
Males > females
Should not change w age
ONH blood supply characteristics and main blood supply
Non fenestrated
Autoregulated (unlike in choroid)
Main supply from posterior ciliary arteries
Autoregulation
Intrinsic ability of vascular beds to maintain a constant level of blood flow regardless of changes in perfusion pressure and metabolic demands.
How does autoreg change with IOP increases??
NO is released and vessels dilate to increase blood flow to tissues. If autoreg does not work, it can lead to ONH damage
Autoreg factors
Endothelin 1 constricts
NO dilates
Axoplasmic flow
Energy dependent process of transmitting cellular material through an axon.
Growth factors (brain derived neurotrophic factor) travels from LGN to ganglion cells. Without, it will lead to glaucoma damage.
2 things that disrupt axoplasmic flow
Pinching of nerve (mechanical) or decreased blood flow to nerve.
Perfusion pressure
Blood flow pressure to the ONH. Balance of BP and IOP.
PP is proportional to ____ and inversely proportional to ___
Blood pressure. Increase BP will increase blood flow to the nerve.
Inverse to IOP bc IOP blocks blood flow to the nerve.
How to calculate PP?
Less than __mmHg may be risk for glaucoma bc perfusion pressure is too low (aka ONH is not getting enough blood flow. autoreg will kick on but can only dilate so far before dysregulation occurs).
Diastolic - IOP
What happens when autoregulatio breaks down
Perfusion pressure increases and causes vessel wall damage to pericytes and may cause atherosclerosis
Ganglion cell types
P: More numerous, at fovea. Small receptive field, sustained stimuli.
M: Even distribution across retina. Responds to transient and low spatial frequency changes in the periphery. Preferentially damaged in glaucoma. VF testing done to evaluate the system.
ON changes- violating ISNT rule and vertical elongation
Poles are at greater risk for damage due to axons entering and the NRR not being able to support them.
ON changes- NRR notching
FOCAL damage or loss within the NRR on the inner edge of the cup. Looks like NRR has been eaten away. Associated with RNFL defect
NRR notching vs pit
notching is focal damage within the NRR on the inner edge of the cup.
Pit is depending of the area within the center cup. Grey, oval appearance.
ON changes= concentric enlargement of cup
3 examples
Deepening. Includes bean potting, bayonetting, and vessel baring
Bean potting and bayonetting appearance due to concentric enlargement of cup
Bean potting: Describes what is happening at the NRR due to excavation.
Bayonetting: Describes vascular appearance of the vessel as it follows the excavated NRR. Like a pencil in water. Z shape.
Vessel baring
Where the NRR used to be. Indicates change and wearing away of the NRR/larger cup.
ON changes- asymmetric C/D
0.2 asymmetry is sus
POAG is bilateral but often symmetric
ON changes- disc hemorrhages
Drance, flame shape. Leads to PPA and VF defect.
Common in NTG
ON changes- vessel changes (4)
- Nasalization: nasal cup as glaucoma starts, vessel nasalization in progressed glaucoma. They fall off to the side bc the tissue is weak.
- Arterial attenuation
- Baring
- Bayonetting
How to evaluate the disc
Small rectangular beam over the nerve
Red free to view ONH and RNFL
Direct medium spot
5 R’s
- Scleral Ring
- Rim eval using ISNT rule
- RNFL
- Region around disc for PPA.
- Beta is closest to the nerve and appears white due to atrophy of RPE and choriocap. Associated with glaucoma.
- Alpha is further from the nerve and appears dark due to RPE pigment changes. Less associated with glaucoma.
5. Retinal/disc hemes
Lamina cribrosa has how many pores and where are they largest at
400-500 pores. Largest at vertical poles
Larger pores= less structural support. Susceptible to tensile strain and impede axoplasmic flow = glaucoma changes.
