Saturday, 23 July 2011

Diagnosing & Treating Glaucoma

Published in "Panorama"

Early Detection can prevent blindness resulting from Glaucoma:

Glaucoma is a leading cause of irreversible blindness around the world. But the good news is, if detected early, the blindness from it is preventable, says Dr.Ratan Bajaj, Eye Specialist and Contact Lens Expert, Ramada Medical Centre, Dubai.

Glaucoma is a group of related conditions in which the optic nerve, the nerve connecting the eye to the brain, is damaged. Most often, this damage is due to an increase in intraocular pressure (IOP) greater than 21mmHg (millimeters of mercury, the same unit used to measure blood pressure). A certain minimum pressure (ranging between 10-21 mmHg) is required to maintain the shape and size of the eyeball and optimalise its function. However, problem arises when the pressure gets too high, becoming higher than the pressure of the blood in the small arteries inside the eye. This leads to the flattening of the tiny arteries supplying the beginning of the optic nerve. Long term partial deprivation of blood to the optic-nerve head gradually destroys the nerve fibres; vision impairment is the consequence, explains Dr.Bajaj.

So how does this eye pressure rise? The eye constantly makes and drains fluid which contains nutrients that are essential for normal eye function. The trabecular meshwork or drain of the eye, is located at the junction of the Sclera, Iris and Cornea, in a part of the eye called the angle. In some individuals, the drainage channel may become less efficient with age resulting in fluid buildup and consequent intraoccular pressure. The condition is termed Primary Open Angle Glaucoma (POAG), the commonest forms of glaucoma, brought about when the fluid drainage angle within the eye is open but the drainage channels are closed. Initially it affects the individual’s peripheral vision, causing tunnel vision, meaning the person is able to see only what is directly ahead of him. Since the condition is symptom-less and the process painless, subtle and gradual, the damage may continue, eventually causing loss of central vision and blindness. The whole process leading to blindness can take many years; hence if diagnosed and treated early, the damage can be arrested and blindness prevented, explains Dr.Bajaj.

The cause of POAG is unknown reveals Dr.Bajaj but ageing and genetic factors are certainly involved. The incidence of POAG rises with age and is equally common in both sexes. Ten per cent of confirmed cases have first degree relatives, that is parents, siblings or children with the disease.

A second form of glaucoma is seen in people where the iris may block the access to the drain, leading to Acute Closed Angle Glaucoma (ACAG). Elaborating on the condition, Dr.Bajaj explains, “The incidence of ACAG is approximately one in 1,000 in people over the age of 40, with a female to male ratio of 4:1. ACAG is characterised by an acute rise in IOP to levels as high as 70-80mmHg. If the angle between the iris and cornea is too narrow, acute glaucoma can occur when the pupil is enlarged by certain medications, or in a darkened room or in cinema theatres. It can be precipitated by stress and emotional upsets. This happens when the iris is pushed against the lens of the eye, shutting off the drainage angle. The patient can present with pain, blurred vision, rainbow-like halos around light, frontal headache, nausea and vomiting. This is a medical emergency, requiring immediate treatment; else permanent vision damage may result.”

ACAG is often caused by some kind of structural defect in the eye. Individuals with myopia or short sight and those with mature cataract are at higher risk of ACAG. Sub acute episodes of angle closure glaucoma may present with few symptoms like frontal headache and nausea and blurring of vision which may disappear after sleep but are likely to recur, thus carrying the risk of an acute attack. In such instances, it is better to have certain tests called Provocative tests done to confirm glaucoma and take appropriate timely measures to prevent further damage, says Dr.Bajaj.

“However, some people with glaucoma may not have a high eye pressure; these people have Normal Tension Glaucoma. On the other hand there are people who have high eye pressure but don’t get glaucoma. These people have Ocular Hypertension and do face the risk of, particularly if their eye pressure is greater than 30 mm Hg,” explains Dr.Bajaj.

Contrary to what many people may believe, glaucoma is not a disease that is limited to the elderly, reveals Dr.Bajaj. In a rare condition, Glaucoma may be present at birth when infants are born with underdeveloped drainage canals. This is usually corrected successfully with surgery.

So who are the people at risk of developing one or the other form of glaucoma? The following categories of people require to be examined for glaucoma, says Dr.Bajaj.
Those above the age of 40.
Those with a family history of glaucoma
Those with high myopia (With power greater than minus 6)
Individuals with retinal vein occlusion
Those on chronic medication with cortico-steroids.

Early detection is very important in diagnosing and treating glaucoma. Tests for eye pressure, optic nerve damage and peripheral vision should be conducted. A comprehensive eye examination for high risk individuals includes taking detailed family history, checking intraocular pressure by tonometry, inspecting drainage angle, examining retinal and optic nerve, evaluating the visual field and examining the back of the eye to see the health of the optic nerve.

There is no cure for glaucoma, but it can be treated and managed in two ways: medication – topical and oral; and surgery – laser and incisional. Both treatment modalities aim to manage the problem by reducing intraocular pressure. While damage already done in terms of vision impairment cannot be reversed, further vision loss can arrested if the condition is diagnosed well on time, before the optic nerve fibres have been destroyed. Dr.Bajaj explains, “Medication is the first line of treatment in Glaucoma, particularly for POAG. However, drugs used in the treatment of POAG and ACAG are different. Surgery is reserved for the minority of patients who do not respond to medication.

Basically four main families of medication are used in treating individuals with POAG: beta blockers like betaxolol, adrenaline-related drugs, miotics like pilocarpine, carbonic anhydrase inhibitors like dimoxol, in that order. Dr.Bajaj, however cautions, “These drugs have side effects; hence we must be very careful in prescribing them, selecting them after taking a thorough medical history of the patients. For instance, Beta Blockers can have adverse effect on individuals with asthma or other lung and heart conditions. Side effects can include low blood pressure, reduced pulse rate, fatigue and depression.”

Explaining the side effects of carbonate anhydrase inhibitors, Dr.Bajaj reveals, “These are basically diuretics and therefore cause more urine output. In addition, they may cause mental confusion, depression, renal stone formation and potassium deficiency. These drugs should therefore be used only as a short term therapy, for 2-3 weeks. If dimoxol also fails, the next course of action is surgery – laser or filtration surgery.”

The type of surgery would again depend on the stage of glaucoma, opines Dr.Bajaj. “In advanced cases of glaucoma where medication has failed, there is substantial vision loss or the visual field is damaged to the extent of 60%-70%, the pressure is high and not well controlled with the drugs, then we don’t go for laser surgery – filtration surgery would be the better option. This is because with the laser surgery we find that the patients cannot see without the drugs, the local drops have to be used following surgery.”

In treating ACAG, the immediate need is to decrease the eye pressure. This is done with medication, given either orally or intravenously. While Beta Blockers may not be used, the drainage of fluid out of the eye can be helped by the instillation of 4% pilocarpine eye drops to contract the pupil and open the pores in the drainage tissue, explains Dr.Bajaj. “However, surgery should almost certainly be followed up in acute cases.”


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