The silent thief of sight.
Writer: Dr Farok Irani (MBBS, Dip Anat, FRANZCO) - eye specialist at EYE SURGEONS BENDIGO
This is the third part of a series looking at eye diseases that affect vision.
Glaucoma is the leading cause of irreversible blindness in the world. Five per cent of Australians will develop glaucoma, yet sadly, 50 per cent of patients with glaucoma remain undiagnosed.
Who gets Glaucoma?
Those with a first-degree relative have an eight-fold increase in risk of developing this disease. Other risk factors include myopia (shortsightedness), hyperopia (long sightedness), diabetes, past trauma to the eye, inflammatory eye conditions and use of corticosteroid drugs.
What is glaucoma?
Glaucoma is a condition where the optic nerve is slowly destroyed. This nerve connects the eye with the brain. Commonly there are very few or no symptoms. Hence it is termed the “silent thief of sight”. Later in the disease there is constriction of peripheral vision and in advanced cases loss of central vision and blindness. Damage occurs because the pressure inside the eye is not appropriate for the health of the optic nerve. In most cases the pressure is high. However in one third of cases the pressure is actually normal – “low tension glaucoma”. The pressure inside the eye is a result of the equilibrium between fluid production and fluid drainage of aqueous humour – the natural liquid made by the eye. People over age 40 should be checked for this condition, and those with a family history earlier. It will involve measuring the eye pressure and checking the visual field – the peripheral extent that a normal eye should be able to see. Other tests such as an OCT may be done to measure the thickness of the nerve fibres that make up the optic nerve. Most importantly, a detailed inspection will be made of the optic nerve itself. This is done by shining a light through the pupil and looking at the back inside part of the eye. In early glaucoma, this will be damaged despite normal visual fields and good vision. Photographs of the nerve are taken to document and record its appearance. Several varieties of glaucoma exist and they may co-exist in any individual. Open angle describes no blockage to fluid egress (just increased resistance). Closed angle describes difficulty for eye fluid to drain out because of mechanical obstruction. Narrow angle describes a propensity for the eye to develop a closed angle. Some eyes have a high pressure but no glaucoma (i.e. no nerve damage) and this is termed ocular hypertension. These must be monitored closely as many will progress to frank glaucoma in time. Any patient with signs not entirely consistent with glaucoma but enough to raise concern are labelled a “glaucoma suspect”. Again, these should be serially monitored.
How is Glaucoma treated?
Treatment is initiated to halt progression of this condition, or just slow it down. Damage done cannot be reversed. Therapies are aimed at lowering the eye pressure. This is done with eye drops and/ or laser, and these are often combined. In advanced or recalcitrant cases, surgery to lower the pressure is performed. Glaucoma patients are monitored serially for life to make sure that the pressure reduction achieved is not only maintained, but that the optic nerve is not suffering further damage. Hence, the optic nerve must be continuously appraised by direct examination, measurement of the eye pressure and ancillary tests such as visual field and OCT.
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