topic 2: glaucoma part 1 Flashcards
what is IOP regulated by?
aqueous production and outflow
Any obstruction to the above will result in raise of IOP
what is glaucoma? what are its 3 characteristics?
Disease of the optic nerve head
characterized by:
1. Loss of optic nerve fibres (cannot be regenerated)
- Corresponding visual field defects
- May or may not have: Raised IOP (commonly associated with glaucoma but not always)
what is the normal iop range and avg iop?
Normal
Range: 10 – 21 mmHg
Mean: 16 +/- 2.5 mmHg
what time of the day is iop highest? what is the normal diurnal variation? (fluctuation of iop through out the day)
morning (AM)
4-6 mmHg
what is tonometry results influenced by?
corneal thickness
thicker cornea=higher iop
what is the mechanical pathophysiology in increased IOP?
- Increased IOP → damage to retinal ganglion cell axons at the level of lamina cribrosa
- Misaligned lamina pores
- Twisted nerve fibres
- Decreased axoplasmic flow
- Optic atrophy
what is the vascular pathophysiology in increased IOP?
- Increased IOP squeezes b/v at ONH
- Splinter haemorrhages at ONH
- ONH infarction/ischemia
what are the 7 structural glaucomatous damages to the ONH
- enlarged cupping (CD ratio)
- neural rim changed (ISNT rule)
- peripapillary atropy (PPA)
- Optic disc hemorrhage
- Laminar dot sign
- B/V changes
- *NFL loss
what is the functional and other 3 glaucomatous damages to the ONH
functional:
1. VF defect
others:
- corneal oedema
- corneal thickness
- ACA change
what is the normal range of cup disk ratio? how much is abnormal
Normal range: 0.3 - 0.4
> 0.5 is suspicious
How do we differentiate physiological from pathological CD ratio abnormality?
Asymmetry of >0.2 is abnormal (pathological)
what are the 2 types of neuroretinal loss?
Notch loss
Diffuse loss
what rule should we follow to evaluate shape? what about size?
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
describe peripapillary atrophy. what are the 2 zones where atrophy might occur?
RPE and choroidal degeneration around the disc
Alpha (outer) zone: superficial RPE changes
Beta (inner) zone: chorio retinal atrophy → may be associated with glaucoma
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?
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
what is the glaucomatous damage seen in the lamina cribosa?
Laminar dot sign (exposed as the neuroretinal rim recedes)
what are the 3 blood vessels changes would you observe? briefly describe them
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
what are the 2 types of NFL loss and the 2 ways to identify NFL loss
types:
Diffuse
Localized
- Striations are absent
- Blood vessels appear dark and sharply defined
what are the 5 Rs of glaucoma evaluation?
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.
what are the 5 types of of vfd that can be detected by VF analyser?
- Paracentral scotoma/enlarged blind spot (earliest sign)
- nasal step
- superior arcuate field loss
- entire superior field loss
- Superior & inferior field loss
what does the frequency doubling perimetry test for?
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
what would loss of ganglion M cells result in?
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
what are the 2 machines used for optic disk imaging? what do they give us?
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
what is the purpose of gonioscopy?
to evaluate the anterior chamber angle structures (need numbing eye drops)
what are the 4 structures that are visible in an open angle?
cilliary body
scleral spur
anterior trabeculum
schwalbes line
what structures are visible in a 75% open angle?
scleral spur
anterior trabeculum
schwalbes line
Higher risk compared to Open angle structures
what structures are visible in a 50% open angle?
anterior trabeculum
schwalbes line
Higher risk compared to Open angle structures
what structures are visible in a 75% open angle?
schwalbes line
Higher risk compared to Open angle structures
what structures are visible in a closed angle?
None of the Angle structures visible
High risk
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