B2 Glaucoma Flashcards
define glaucoma
it is the disease of the optic nerve head characterised by:
- loss of optic nerve head fibres (NFL) and its corresponding visual field defects
- potentially raised IOP
state normal IOP (range and mean) and diurnal variation
normal: 10-21 mmHg (range), 16 +- 2.5 mmHg (mean)
diurnal variation: higher in the morning than afternoon, 4-6 mmHg (normal variation)
how is IOP measured
by tonometry
highly influenced by corneal thickness (thicker cornea -> higher IOP)
when assessing IOP, risk factors must be taken into account ie. medication, refractive surgery
state and explain 2 pathophysiological aspects to glaucoma
mechanical theory: IOP increase causes damage to retinal GLC axons which cause NFL to eventually die leading to ONH atrophy
vascular theory: IOP increase causes blood vessels at ONH to be squeezed, hence ONH undergoes infarction/ischemia (lack of O2). splinter haemorrhages may be seen but will subside if IOP returns to normal
state classifications of glaucomatous changes
ONH damage (enlarged cupping, neural rim changes, signs of peripapillary atrophy, optic disc haemorrhage, laminar dot sign, b/v changes, NFL loss) …
…and its corresponding VF defects
others: corneal oedema/thickness changes/AC angle changes
explain ONH changes (glaucomatous)
- c-d ratio: 0.3 to 0.4 (normal), >0.5 suspicious, asymmetry > 0.2 suspicious
- neuroretinal rim thickness: loss (notching/thinning) of sequence in thickness (ISNT) can indicate loss of NFL ((glaucoma usually causes vertical thinning))
- peripapillary atrophy: common in high myopes, RPE (alpha zone) and choroidal (beta zone) degeneration which happens when the RPE pulls away from the ONH revealing the choroid or sclera. in the beta zone, chorio retinal atrophy may be associated with glaucoma
- haemorrhage (drance/splinter): occurs where NF present, often adjacent to NF thinning, temporary (IOP stabilises)
- lamina cribosa dot sign: becomes more obvious due to receding NRR/loss of NRR (loss of NFL)
- blood vessels: nasal sweep, baring (hangs over ONH, poor support to BV), bayoneting (sharp exit from ONH)
- NFL loss: different in colour can be seen in fundus imaging to show NFL loss or bvs appear darker and sharply defined. normally starts at inferior (recall NF never cross temporal raphe). diffused/localised, striations are absent
state 5 R’s for glaucoma evaluation
(scleral) RING - observe optic disc size
(neuroretinal) RIM - observe NRR size&shape / i.s.n.t.
RNFL
REGION of peripapillary atrophy
(hemo)RRHAGES - presence of retinal or optic disc haemorrhages
instruments to detect for possible glaucoma
VF analyser (stages of glaucoma): starts off with enlarged blind spot/paracentral scotoma, nasal step, (superior/inferior) arcuate field loss, entire (superior/inferior) arcuate field loss, superior & inferior arcuate field loss
frequency doubling perimeter (early glaucoma): measures ganglion M cells which are bigger in diameter and more susceptible to glaucomatous changes. loss of these cells causes considerable loss of visual function
OCT & HRT (structural loss): capture the images of the optic disc to measure the CD ratio, NRR thickness and the Retinal Nerve Fiber Layer (RNFL) thickness.
gonioscopy: gold standard for AC angle assessment, this technique allows actual visualisation of AC angle structures unlike other methods.
what are some symptoms of glaucoma (if not asymptomatic)
pain, redness, watering of eyes
blurred vision
nausea & vomitting
haloes
bumping into objects while walking (due to diminishing peripheral vision)
explain referral guideline & management for glaucoma
van herick angle <0.25: symptomatic of ACG (haloes, headache, blurred vision) refer within 3 days, asymptomatic is non-urgent referral
disc >0.7/thinning or notching of NFL/asymmetry >0.2: non urgent referral and advice accordingly to sheet
IOP > 22mmHg (avg of 4 readings and taken on 3 different occasions): 22-25 non urgent, 25-35 early, >35 3 days, AACG immediate, and according to advice sheet
glaucomatous VF defect: according to urgency appropriate to clinical assessment
explain ocular hypertension
when the patient’s IOP is higher than normal but show no detectable glaucomatous change.
4-7% of individuals older than 40 have OHTN. OHTN has 10% chance of progressing to glaucoma in 5 years
risk factors of progression from OHT to glaucoma: IOP >/= 30mmHg, greater age, thin central corneal thickness, larger c/d ratio
describe POAG
most common, chronic, usually bilateral but asymmetrical
AC angle is open but outflow is slow. meaning AC angle structures may be blocked ie. TM
risk factors: more in black people, age 40-60 and risk increasing with age, high myopia, fm hx 1st degree 1/10 risk, systematic diseases (DM, HTN), smoking, steroid use, ocular (constantly high IOP, higher myopia, large cd ratio, retinal disease CRVO RP)
explain ssx of POAG
signs: glaucomatous changes, open & normal filtration angle
symptoms: usually asymptomatic though they may start to lose their peripheral vision with time (by then 40% damage is done). therefore, regular eye exams and hx taking important
explain ssx of POAG
signs: glaucomatous changes - IOP may be normal, open & normal filtration angle
symptoms: usually asymptomatic though they may start to lose their peripheral vision with time (by then 40% damage is done). therefore, regular eye exams and hx taking important
explain management of POAG
IOP reduction: the greater the damage, the greater the IOP reduction
urgent referral for medical Tx (first choice)
regular follow up: 6-12 months
