introduction to the glaucomas Flashcards
define glaucoma
the name given to a group of ocular conditions that produce a characteristic optic neuropathy called: glaucomatous optic neuropathy (GON)
what happens as a result of glaucomatous optic neuropathy
RGC’s die in the retina, and hence lose vision
how many % of glaucomas does primary glaucoma account for
> 95%
how does primary glaucoma occur
occurs without any preceding ocular or systemic disease, so occurs because of elevated pressure and nothing else is associated with the glaucoma, the result is optic neuropathy
how much % of glaucomas does secondary glaucoma account for
how much % does primary angle closure glaucoma account for in primary glaucomas
15% of the primary glaucomas in the UK
how much % does primary (chronic) open angle glaucoma (POAG/COAG) account for in primary glaucomas
85% of the primary glaucomas in the UK
what happens as a result of glaucomatous optic neuropathy
RGC’s die in the retina, and hence lose vision
what two mechanisms are associated with open angle glaucoma are being studies
- mechanical: lamina cribrosa
- immune component: passes way to optic nerve through lamina cribrosa & causes ischemia to the optic nerve i.e. blood supply to it
how does secondary glaucoma occur
it is caused by something else, e.g. anterior uveitis, drugs, alcohol, steroids etc
how much % does primary angle closure glaucoma account for in primary glaucomas
15% of the primary glaucomas in the UK
how much % does primary (chronic) open angle glaucoma (POAG/COAG) account for in primary glaucomas
85% of the primary glaucomas in the UK
why do we have to measure IOP in patients over 40 years
because the prevalence of them having primary chronic open angle glaucoma is 2% in the UK
what is the prevalence of patients over 75 years having primary chronic open angle glaucoma
10% of POAG in the UK
list the 3 types of primary glaucomas
- primary angle closure glaucoma
- primary (chronic) open angle glaucoma (POAG or COAG)
- congenital glaucoma
how does primary angle closure glaucoma occur
a close in the angle between the iris and the lens, causing a sudden high IOP, and this prevents aqueous outflow from the anterior chamber
name two causes of primary congenital glaucoma
- bupophthalmos
- micro ophthalmia
what two mechanisms are associated with open angle glaucoma are being studies
- mechanical - lamina cribrosa
- immune
what is the possible definition of open angle glaucoma
optic nerve ischemia
what is the important risk factor that causes open angle glaucoma
- IOP which is raised above average levels
- genetic factors i.e. it can run down the family
= higher risk of developing OAG
why must primary chronic open angle glaucoma be detected as soon as possible
it is asymptomatic until the late stages of the disease
what does the smith method test
the anterior chamber depth
what does the smith method not look at
the anterior chamber angle
what 2 other things can the value of an IOP measurement be complicated by
- diurnal variation in IOP
- ocular hypertension: high IOP but not P(C)OAG
what is ocular hypertension? and what two things must be considered when ruling out ocular hypertension
high IOP >21mmHg but everything else is normal e.g. optic disc, visual fields and an open anterior chamber
- consider age of px: when applying 21mmHg as a threshold, because for an older px a threshold of 18-19mmHg is possible
- is theres >2mmHg different in IOP between the eyes e.g. 13 & 16mmHg, this means there is a risk of the px having glaucoma, even if it is ‘normal’
what do approx. 50% of patients with POAG have at the time of diagnosis and so what must be considered
pressures within the normal range at the time of diagnosis (normal tension glaucoma)
so consider the 5 points as having low pressures doesn’t mean they don’t have glaucoma
describe the changes in visual fields, that is characteristic of someone who has primary open angle glaucoma
- the axons of the RGC’s will respect the horizontal midline, but doesn’t respect the vertical midline as glaucoma is anterior to the chiasm
- the earliest visual field defect is some sort of loss in the mid periphery
- the scotoma becomes arcuate, running along the raphe of the ganglion cells, still respecting the horizontal midline
- another scotoma can occur later, which builds to the arcuate shape
- in later stages, there will just be tunnel vision left
these are characteristic visual field losses but not diagnostic of glaucoma
what level of IOP will a thin cornea always have
low IOP, which is normal
what level of IOP will a thick cornea always have
high IOP, which is normal
what must be considered in conjunction when measuring IOP
central corneal thickness
there is a 10mmHg variance in IOP depending on corneal thickness
what does the smiths method test
the anterior chamber depth
what does the smiths method not look at
the anterior chamber angle
what is observed of the neural retinal rim when looking at sectoral and diffuse pallor
- as nerve fibres die, the disc becomes paler
- colour is a subjective judgement (1-4) grade
- 0 = white (dead and atrophic)
- 1 = grey
- 2 = pink (healthy)
- 4 = hyperaemic/red (papillodema)
what is considered a narrow anterior chamber depth when using the smith method
what 4 things can complicate the value of visual field measurement, when assessing for glaucoma
- there may have been considerable nerve fibre death before the patient has a definite field defect
- visual fields are very subjective - there is much variability
- learning and fatigue effects - causes variable/unreliable results
- 30-2 sita or data need full threshold data to progress data later on (don’t do supra threshold as can miss points and won’t know the true DB/value of that point, so can’t do follow up on a chronic glaucoma px) this is the baseline if the patient has family history of primary open angle glaucoma
describe the changes in visual fields, that is characteristic of someone who has primary open angle glaucoma
-
what is the variability of visual field loss as it changes over time due to
- variability associated with visual fields tests
but shows a pattern of isolated scotomas respecting the midline = ONH disease ~glaucoma
what is used to assess the disc and retinal nerve fibre layer
serial imaging:
- direct and indirect ophthalmoscope, with volk binocular view (as you can see the depth of cupping more easily)
- conventional photography e.g. fundus photography
- optical coherence tomography (OCT)
- scanning laser polarimetry (SLP)
what is the appearance of the nerve fibre layer where glaucomatous damage has occurred
less clearly visible as thickness is reduced and the retina appears darker
viewed with green light on ophthalmoscope i.e. red free light, where you can see axon loss within the ganglion cell layer of retinal nerve fibre layer
what is the neural retinal rim
layer of neural tissue between the edge of the disc and edge of the cup
list the 3 factors to assess of the neural retinal rim
- sectoral or diffuse pallor
- focal notching - irregularities in the rim
- ISNT rule: inferior thicker than superior thicker than nasal thicker than temporal, in a healthy eye
what is observed of the neural retinal rim when looking at sectoral and diffuse pallor
- as nerve fibres die, the disc becomes paler
- colour is a subjective judgement (1-4) grade
- 0 = white (dead and atrophic)
- 4 = hyperaemic (papillodema)
what value of vertical c/d ratio is considered suspicious to glaucoma
0.6
what does a change in c/d ratio of 0.2 or more throughout time suggest
neuronal damage in the arcuate fibre area
what must you look for with c/d ratio between the two eyes
a difference in c/d ratio between the eyes
- an asymmetry of 0.2 or more in c/d ratio is suspicious
- but cup size depends on disc size - the larger the disc the larger the cup, so a big cup in a small disc is suspicious
how can you use an ophthalmoscope to assess the depth of a cup
to focus the ophthalmoscope of a BV e.g. +2D, then focus on that BV when its in the cup e.g. with a +4D = 2D cup depth
what does dots in the cup indicate
it is the lamina cribrosa, will look grey and indicates a deep cup
what is the appearance of the nerve fibre layer where glaucomatous damage has occurred
less clearly visible and the retina appears darker
viewed with green light on ophthalmoscope i.e. red free light, where you can see axon loss within the ganglion cell layer of retinal nerve fibre layer
when does haemorrhages at the optic disc most frequently occur
- in cases of normal tension glaucoma
- ocular hypertension
- trauma
- can sometimes just happen, e.g. come and go so is not a large association with glaucoma
what is the prevalence of ocular hypertension in the adult population
between 2.7 and 7.5%
what is the first step in treatment, to aim for a ‘target’ IOP
first use topical drugs to lower IOP e.g.
- prostaglandin analogues
- beta blockers
aims to get IOP below 21mmHg
if topical drugs does not work in achieving a target IOP of 21mmHg, what is the next step in treatment
consider surgery
- laser
- conventional
to open the trabecular meshwork through surgery
