GLAUCOMA 6 - assessment of optic disc in POAG Flashcards
what is glaucoma characterised by??
retinal ganglion cell dysfunction and death
before you develop a VF defect, how much of your nerve fibres need to die?
25%
what is the OHTS study?
ocular hypertension treatment study 2002
in glaucoma, are you more likely to observe an optic disc change or a VF defect??
optic disc change
what structure marks the edge of the neuro retinal rim?
Elschning scleral ring
which structure haas a yellow-white ‘sieve-like’ appearance?
lamina cribrosa
how do you measure disc size?
from the inner part of the rims on either side
what is the ISNT rule?
NRR is widest inferior, superior, nasal then temporal
what section of the disc is likely to show thinning in glaucoma EARLY STAGES? (isnt rule)
infero-temporal region
what section of the disc is likely to show thinning in glaucoma LATE STAGES? (isnt rule)
can be nasal
if you have a large disc/scleral opening are you more likely to have a larger or smaller cup?
large cup
if you have a small disc/scleral opening, are you more likely to have a larger or smaller cup?
small cup
how many nerve fibres are going through the scleral opening of the ONH?
1.2 million
what is the scleral canal/opening?
where the nerve fibres run through the optic disc
what are the key optic disc changes in glaucoma?
- enlargement of optic cup
- loss of NRR
- vascular changes (haemorrhages and distribution of vessels)
- increased pallor
- peri-papillary atrophy
- RNFL changes
if pallor is the biggest change to the optic disc, is glaucoma the only disease to be considered?
NO - consider other optic neuropathies e.g AION
pallor is a late sign in glaucoma
is enlargement of the optic cup generalised or localised?
can be both !
is vertical cupping or horizontal cupping more indicative of glaucomatous changes?
vertical cupping
if you have inter-eye asymmetry, what do you need to check for?
the disc sizes are the same - if not this could be physiological
what is the diagnostic accuracy of measuring CD ratios?
poor sensitivity and poor specificity
limited
what are the disadvantages of measuring CD ratios?
poor diagnostic accuracy - poor sensitivity/specificity
inter/intra-observer variability
what is the lens magnification factor for a superfield?
1.5
what is the lens magnification factor for a 66D volk?
1.0
what is the lens magnification factor for a 90D volk?
1.4
what is the lens magification factor for a 78D volk>
1.1
when assessing VFs, you need to look for asymmetry…
between the 2 eyes
AND
between the superior and inferior hemi fields (GHT)
what are the vascular changes that can occur in glauc?
- vessel configuration (nasalisation, bayonetting, flyover/overpass, circumlinear bearing)
- calibre of vessels can be thinner at optic disc
- collateral vessels
- haemorrhage
what are collateral vessels?
occur when someone has had a CRVO which can be associated with high IOP
OPTOCILIARY SHUNT VESSELS
what are the main changes you need to be looking for when assessing if a disc is glaucomatous or not?
cupping changes and thinning of NRR
a disc haemorrhage is a sign of..
active progression
which type of glaucoma are disc haemorrhages common in?
NTG
other than glaucoma what is a common cause for a disc haemorrhage?
PVD
are haemorhhages constantly there?
no - they can be reabsorbed
what does this image show?
disc haemorrhage
what does this image show?
disc haemorrhage, little cupping
could be due to PVD
what does this image show?
large inferior haemhorrhage
what does this image show?
superior haemorrhage in thte RNFL as it is radiating away from disc
you can get peri-papillary atrophy in 2 zones - what are these called?
alpha zone and beta zone
out of aloha and beta zones, which is worse??
beta
(remember B for BAD)
what is peri-papillar atropy associated with?
NRR loss and VF defect
what do these images show?
peri-papillary atrophy
optic disc checklist!!
- Is the vertical C/D ratio >0.5?
- Is the C/D ratio consistent with disc size?
- Is the cup more vertically oval than the disc?
- Does rim configuration differ from ‘ISNT’?
- Are there any notches or pallor regions in the nrr?
- Are there any disc haemorrhages ?
- Is the inter-eye C/D ratio asymmetry >0.2?
- Has there been a >0.15 change in C/D ratio?
CD ratio??
0.7-0.85 (about 1.5 difference per person)
what is the DDLS?
disc damage likelihood scale
how do you grade the disc size according to DDLS?
measure disc size (correct for volk magnification)
small = <1.5mm
medium = 1.5-2 mm
large = >2.0mm
how do you measure width of thinnest part of the rim for DDLS?
rim - disc ratio
if no rim oresent at thinning part = 0
if rim as thick as possible (no cup) = 0.5
IF YOU HAVE SEEN PX BEOFRE how much difference in the CD ratio does there need to be for you to say there has been a change??
0.15
IF YOU HAVEN’T SEEN PX BEFORE how much difference in the CD ratio does there need to be for you to say there has been a change?
0.25
what does this image show?
optic atrophy
what does this image show?
RNFL assessment - inferior cupping with notched rim
dark shadow extending inferior temporally from the disc = nerve fibre layer defect
what does this image show?
wedge-like defect in RNFL
associated with inferior VF defect in the Px’s RE
what does this image show?
wedge-like defect in RNFL
associated with inferior VF defect in the Px’s RE
which 3 systems are good for imaging the optic nerve head?
OCT
heidelberg retina tomograph (HRT)
GDx VCC
if you have an abnormal finding on one machine, does that mean they have glaucoma??
NO - need to asses all clinical information together
what does this image show?
pseudoexfoliation in the lens = flakes and sheets of exfoliative material
can be cause of secondary glaucoma
what are some examples of congenital disc abnormalities?
coloboma
optic disc pit
tilted disc
drusen
myelinated fibres
myopic disc
what does this image show?
myopic disc
what does this image show?
tilted disc potentially has glaucoma as well
what does this image show?
optic disc drusen
other than glacuoma, what other conditions can cause nerve fibre bundle defects?
- optic nerve head drusen
- congenital optic nerve head pits
- coloboma of optic nerve
- AION
- tilted disc
is this disc physiological or pathological?
physiological- ISNT rule is followed,
is this disc physiological or pathological?
pathological - superior rim is thinner than temporal, vertically excavated
what does this image show?
what does this image show?
what does this image show?
