This group of eye conditions is the second leading cause of blindness in the world, mainly affecting the middle-aged and elderly.
Glaucoma usually occurs when an increase in fluid pressure within the eye (intraocular pressure or IOP) damages the optic nerve, which transmits nerve impulses for sight to the brain. The nerve fibres in the retina may also be affected. As these changes are permanent, the loss of vision is irreversible.
The ‘angle’ refers to the internal group of structures which include a trabecular meshwork that allow the drainage of fluid (aqueous) from the anterior chamber of the eye.
This is the commonest form of glaucoma and results from an excess of aqueous or a blockage in the trabecular meshwork, causing an increase in the IOP. It is often referred to as the ‘silent thief of sight’ as the onset is insidious and the increase in IOP slow. The patient does not experience any symptoms until it has progressed to a late stage.
Peripheral (side) vision and night vision are gradually affected first; central or reading vision is only affected very late.
Risk factors for POAG include:
This accounts for 10 percent of glaucoma cases and in Singapore, usually affects middle-aged to elderly Chinese women. It is caused by an anatomical apposition of the iris onto the angle tissue, thus blocking the drainage of aqueous and increasing the IOP.
ACAG, in contrast to POAG, is an acute medical emergency, as the increase in IOP occurs suddenly and progresses rapidly.
The symptoms include:
Risk factors for ACAG include:
This also results from a blockage of the aqueous outflow but unlike ACAG, the build-up in IOP is gradual.
This results from the raised IOP caused by other conditions like tumours or inflammatory diseases of the eye, use of certain medications and injuries or surgery to the eyeball.
This occurs in infancy, childhood and adolescence and results from an inherited developmental abnormality that blocks the aqueous outflow.
Glaucoma cannot be prevented. However,the earlier it is detected and treatment started to reduce the IOP, the better the chances of slowing down its progression towards visual loss. Hence, regular eye checks for high-risk groups is recommended.
The eye tests for glaucoma include IOP measurement, optic nerve and aqueous drainage examinations and a visual field assessment.
There is NO CURE for glaucoma but there are effective means to control it. All are aimed at reducing and controlling the eye pressure such that visual loss is minimized. The eye doctor will be able to advise on which treatment options are most suitable.
When medications are not sufficient to control the pressure, laser surgery can be employed to help the outflow of fluid. The methods are:
If medications and laser treatment are not successful, trabeculectomy can be performed. In this procedure, a new opening is created in the trabecular meshwork for fluid to leave the eye.
All the above-mentioned procedures are done on an outpatient basis.
Due to the progressive nature of glaucoma, lifelong monitoring and/or treatment is necessary for effective control of this condition and to preserve sight as much as possible.