topic 2: glaucoma part 1

Question 1

what is IOP regulated by?

Answer 1

aqueous production and outflow

Any obstruction to the above will result in raise of IOP

Question 2

what is glaucoma? what are its 3 characteristics?

Answer 2

Disease of the optic nerve head

characterized by:
1. Loss of optic nerve fibres (cannot be regenerated)

2. Corresponding visual field defects
3. May or may not have: Raised IOP (commonly associated with glaucoma but not always)

Question 3

what is the normal iop range and avg iop?

Answer 3

Normal
Range: 10 – 21 mmHg
Mean: 16 +/- 2.5 mmHg

Question 4

what time of the day is iop highest? what is the normal diurnal variation? (fluctuation of iop through out the day)

Answer 4

morning (AM)

4-6 mmHg

Question 5

what is tonometry results influenced by?

Answer 5

corneal thickness

thicker cornea=higher iop

Question 6

what is the mechanical pathophysiology in increased IOP?

Answer 6

1. Increased IOP → damage to retinal ganglion cell axons at the level of lamina cribrosa
2. Misaligned lamina pores
3. Twisted nerve fibres
4. Decreased axoplasmic flow
5. Optic atrophy

Question 7

what is the vascular pathophysiology in increased IOP?

Answer 7

1. Increased IOP squeezes b/v at ONH
2. Splinter haemorrhages at ONH
3. ONH infarction/ischemia

Question 8

what are the 7 structural glaucomatous damages to the ONH

Answer 8

1. enlarged cupping (CD ratio)
2. neural rim changed (ISNT rule)
3. peripapillary atropy (PPA)
4. Optic disc hemorrhage
5. Laminar dot sign
6. B/V changes
7. *NFL loss

Question 9

what is the functional and other 3 glaucomatous damages to the ONH

Answer 9

functional:
1. VF defect

others:

1. corneal oedema
2. corneal thickness
3. ACA change

Question 10

what is the normal range of cup disk ratio? how much is abnormal

Answer 10

Normal range: 0.3 - 0.4

> 0.5 is suspicious

Question 11

How do we differentiate physiological from pathological CD ratio abnormality?

Answer 11

Asymmetry of >0.2 is abnormal (pathological)

Question 12

what are the 2 types of neuroretinal loss?

Answer 12

Notch loss

Diffuse loss

Question 13

what rule should we follow to evaluate shape? what about size?

Answer 13

Shape = ISNT rule

thickest Inferiorly, followed by superiorly, then nasally and thinnest temporally.

With glaucoma, you begin to see vertical thinning, with atrophy along the inferior and superior rims. (usually inferior region starts thinning first)

Size varies according to disc size

Question 14

describe peripapillary atrophy. what are the 2 zones where atrophy might occur?

Answer 14

RPE and choroidal degeneration around the disc

Alpha (outer) zone: superficial RPE changes

Beta (inner) zone: chorio retinal atrophy → may be associated with glaucoma

Question 15

what are the 2 types of haemorrhages that may occur in the ONH? where do they occur and what happens to them when iop returns to norm?

Answer 15

Drance haemorrhage / splinter haemorrhage

Occurs in areas where nerve fibres are present, often adjacent to thinned areas where the nerve fibres are lost

Will disappear once IOP is normal

Question 16

what is the glaucomatous damage seen in the lamina cribosa?

Answer 16

Laminar dot sign (exposed as the neuroretinal rim recedes)

Question 17

what are the 3 blood vessels changes would you observe? briefly describe them

Answer 17

Baring–blood vessels hang over ONH and have poor support underneath due to loss of NRR

Nasal sweep–BV move over to the nasal side

Bayoneting– sharp angle of exit of BV out of ONH

Question 18

what are the 2 types of NFL loss and the 2 ways to identify NFL loss

Answer 18

types:
Diffuse
Localized

1. Striations are absent
2. Blood vessels appear dark and sharply defined

Question 19

what are the 5 Rs of glaucoma evaluation?

Answer 19

Observe scleral *ring to evaluate optic disc size

Neuroretinal *rim size and shape (ISNT rule), notching

• Retinal nerve fiber layer
• Region of peripapillary atrophy

Presence of *retinal or optic disc hemorrhages.

Question 20

what are the 5 types of of vfd that can be detected by VF analyser?

Answer 20

1. Paracentral scotoma/enlarged blind spot (earliest sign)
2. nasal step
3. superior arcuate field loss
4. entire superior field loss
5. Superior & inferior field loss

Question 21

what does the frequency doubling perimetry test for?

Answer 21

test for Ganglion M cells with relatively large diameter axons (comprise 25% of the ganglion cell population)

These cells are particularly susceptible to glaucomatous damage and appear to be preferentially lost in early glaucoma

Question 22

what would loss of ganglion M cells result in?

Answer 22

A loss of a small number of these cells has a considerable effect on visual function

Frequency doubling perimetry based on the above principle is used as a screening tool to detect early glaucoma

Question 23

what are the 2 machines used for optic disk imaging? what do they give us?

Answer 23

OCT and HRT\

Both capture the images of the optic disc to measure the CD ratio, NRR thickness and the Retinal Nerve Fiber Layer (RNFL) thickness.
tells us about any structural loss

Question 24

what is the purpose of gonioscopy?

Answer 24

to evaluate the anterior chamber angle structures (need numbing eye drops)

Question 25

what are the 4 structures that are visible in an open angle?

Answer 25

cilliary body

scleral spur

anterior trabeculum

schwalbes line

Question 26

what structures are visible in a 75% open angle?

Answer 26

scleral spur

anterior trabeculum

schwalbes line

Higher risk compared to Open angle structures

Question 27

what structures are visible in a 50% open angle?

Answer 27

anterior trabeculum

schwalbes line

Higher risk compared to Open angle structures

Question 28

what structures are visible in a 75% open angle?

Answer 28

schwalbes line

Higher risk compared to Open angle structures

Question 29

what structures are visible in a closed angle?

Answer 29

None of the Angle structures visible

High risk

Question 30

LOOK AT REFERAL GUIDELINE TABLES

Answer 30

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