gradual loss of vision glaucoma Flashcards
what is the angle
the anngle is the name given to the space between the posterior cornea and the anterior surface of the iris
this is where the aqeuous leaves the eye
glaucoma classification
Anatomic-Open angle or closed angle
Presentation-Chronic or acute
Cause-Primary or secondary
The most common type of glaucoma is chronic open angle glaucoma also called chronic simple glaucoma
aqueous humour - how is it produced
Aqueous is produced in the ciliary body
It circulates around, and provides nourishment for, the lens
It passes through pupil into the anterior chamber
It leaves eye via the trabecular meshwork in the angle and enters the episcleral veins
what is iop and what are the normal values
IOP is a balance between aqueous production by the ciliary body and aqueous drainage through the angle
If aqueous drainage is impaired, the IOP rises
Normal IOP is below 21 mm Hg (defined as 2 standard deviations above the mean)
what is chronic open angle glaucoma
COAG is a chronic progressive optic neuropathy with gradual loss of nerve fibres
80% of patients have IOP > 21mmHg
There is enlargement of optic disc cup (loss of neurones), and
Progressive loss of visual field (leading to tunnel vision)
what are glaucoma syndromes
Manifest glaucoma
Patients have high IOP, large cup, field loss
Glaucoma suspect
Patients have abnormal disc or field loss but not both
Ocular hypertension
Patients have high IOP but normal disc and field
Normal Tension Glaucoma
Patients have large cup and field loss but normal IOP
Secondary glaucoma
E.g. after trauma, use of steroids, inflammation
what is optic disc cupping
Most optic discs have a central physiological cup which usually has a diameter less than half of the disc diameter
The cup is the part of the disc without nerve fibres and blood vessels
Small optic discs have small cups and still be healthy
Large optic discs can have large cups and still be healthy
what field loss would you expect in acute open angle glaucoma
Arcuate scotomas begin in superior or inferior visual field
These join up to produce a ring scotoma
This extends to produce tunnel vision
Eventually central vision is lost
Visual acuity remains good until very late in the condition
how is glaucoma identiifed
Patients are asymptomatic until late
Most are picked up by opportunistic ‘screening’ by opticians
Screening by IOP has low specificity with a high false positive rate (FPR)
Visual field testing has similar high FPR
Identification by cupping-poor inter and intraobserver agreement
Best sensitivity and specificity by a combination of all three tests
how is chronic opened angle glaucoma managed
COAG can be managed by:
Observation: mainly ocular hypertension
Medical therapy: drops (rarely oral therapy)
Laser therapy: laser trabeculoplasty, ciliary body laser, laser iridotomy
Surgery: trabeculectomy, deep slcerectomy
what meidcal therapy is given for chronic open angle glaucoma
Topical
Beta-blockers e.g. timolol
Prostaglandins e.g. latanoprost
Carbonic anhydrase inhibitors e.g dorzolamide
Alpha adrenergics e.g. brimonidine
Miotics e.g. pilocarpine
Oral
Carbonic anhydrase inhibitors e.g. acetazolamide
what is the aim of treatment in chronic open angle glaucoma
To stabilise visual field loss
To reduce risk of further progression
To maintain central visual field
Once lost, visual field cannot be recovered
