Glaucoma Flashcards
what is glaucoma?
group of diseases characterised by progressive optic nerve damage and visual field loss
raised IOP
pathogenesis of glaucoma?
usually due to blockage of aqueous outflow leading to raised IOP which causes damage and loss of retinal fibres at optic disc resulting in visual field loss
which visual fields are lost first in glaucoma?
peripheral
periphery has several photoreceptors connecting to 1 ganglion cell whereas 1 photoreceptor connect to several ganglion cells at macula
therefore damage to 1 ganglion cell at periphery causes lots of photoreceptors to be lost
signs of glaucoma?
peripheral field loss
raised IOP
optic disc cupping
how can glaucoma be tested for?
tonometry (tests IOP)
visual field testing
clinical examination to look at optic nerve
how is normal IOP defined?
normal range = within 2 standard deviations above and below the mean IOP
(16-21mmHg)
how is applanation tonometry done?
instrument used to press down on eyeball to measure pressure inside
like pressing on a football to test the air pressure inside
how are visual fields assessed?
goldman fields or other modern methods
both show arcuate defect (arc of visual field loss around centre)
why can glaucoma be last to present?
gradual loss of visual field so the brain fills in the gaps and you dont really notice it
what is cupping and why does it happen in glaucoma?
where the cup in the middle of the optic disc becomes larger in relation to the disc as a whole
due to nerve fibres in the optic nerve dying off so the cup expands to fill the space
what else can be seen at the optic disc in glaucoma?
haemorrhages
types of glaucoma
open angle (primary or secondary) closed angle (primary or secondary) most are open angle
what can cause secondary closed angle glaucoma?
diabetes where new poor quality vessels form and ischaemia occurs, central retinal vein occlusion can also cause
what can cause secondary open angle glaucoma?
cells in the eye (WCCs in uveitis or RBCs from trauma or haemorrhage) can increase pressure, occlude vessels and block drainage angle
what causes primary open angle?
unknown
raised IOP due mainly to blocked drainage of aqueous somehow
may be vascular
(2nd most common cause of blindness in UK)
risk factors for primary open angle?
age
raised IOP
afro-carribean origin
family history
aim of treatment in primary open angle?
need to lower IOP to point where it wont cause further damage within patient’s lifetime (so lower pressure needed in younger people)
what drugs can be used in glaucoma?
beta blockers CA inhibitors prostaglandins/prostaglandin analogues parasympathomimetics sympathomimetics
what do prostaglandins/analogues do?
block outflow through the iris by making iris vessels more leaky
increase uveoscleral outflow
side effects of prostaglandins?
well tolerated
can make iris darker and increase lash growth but patients usually dont care
what do beta blockers do?
reduce aqueous secretion (turn off the tap)
side effects of beta blockers?
cant use in asthma
can cause bradycardia, heart block etc
effects can decrease with time as beta receptors are upregulated
what do carbonic anhydrase (CA) inhibitors do?
reduce aqueous secretion (turn off tap)
side effects of CA inhibitors?
no systemic effects
acidic so stings when going in and can cause local irritation
