Now you see, Now you don't - Glaucoma, the silent blinding eye condition

By

Dept of Ophthalmology,

RIPAS Hospital

Blind Indonesian students playing chess inside their room at a rehabilitation centre in Jakarta, Indonesia. According to the World Health Organisation, more than 161 million people are visually impaired worldwide; among them some 124 million have low vision and about 37 million are blind. Another 153 million people suffer from visual impairment due to uncorrected refractive errors. More than 90 per cent of the world's visually impaired people live in low- and middle-income countries. The most common causes of blindness all over the world are cataract, glaucoma, cornea disorder, macula degeneration and diabetic retinopathy. epa

Courtesy of WHO

Glaucoma is a spectrum of related diseases. Increased pressure in the eye is a measurable problem in this disease. Increased pressure can occur due to a variety of reasons. When the pressure in the eye is high it can cause damage to the optic nerve, which transmits visual information from the eye to brain.

Glaucoma is the second most common cause of blindness worldwide, where 4.5 million persons globally are blind due to glaucoma and is expected to rise to 11.2 million by 2020. Up to 90 per cent of affected persons may not even aware of having the disease.

Glaucoma affects more than 4.5 million people worldwide of whom 10 per cent or 6.6 million people are blind. Glaucoma is the leading cause of irreversible blindness and is second only to cataract as the most common cause of blindness.

The prevalence of glaucoma in Southeast Asia (Singapore) is 4.7 per cent. No population-based data of glaucoma prevalence in Brunei Darussalam is currently available. However, extrapolating the prevalence in the region, about 13,000 should have glaucoma. But studies have shown that 50 per cent of glaucoma remains undiagnosed and at least 10 per cent of the people are blind in one eye at the time of diagnosis .It is commonly seen after 40 years of age and the chance of getting the disease increases with advancing age.

The inheritance of glaucoma still remains obscure. Family history of glaucoma can be seen in 50 per cent of the relatives in one kind of glaucoma. Trauma to the eye can also cause glaucoma.

There are certain groups of people who have increased risk of developing glaucoma; people with diabetes, myopia (short-sightedness), old age, small eyes, family history of glaucoma, migraine, high blood pressure and severe acute low blood pressure. These high-risk people should be evaluated early at the age of 40 and at regular intervals thereafter.

The fluid inside the eye is called the aqueous humor, which is formed by specialised cells. This fluid maintains the pressure normally up to 21mm Hg in normal eyes. This fluid is necessary to carry the nutrients to important structures and removes waste products. The fluid moves out of the eye through small channels to the blood circulation. When the normal flow of the fluid gets blocked the pressure inside the eye can build up causing damage to the optic nerve.

Damage to the optic nerve can cause blind areas in the outer side of vision, which is the beginning of the damage. As the disease gets worse only the central tunnel of vision remains. What is common to all glaucoma is the visual loss that cannot be reversed. Hence early diagnosis and management is very important.

There are two types of glaucoma - open angle and closed angle. In open angle glaucoma the normal drainage channels of the eye is anatomically open but does not function normally. When the fluid cannot leave the eye, the pressure builds up and eventually causes vision damage. This causes painless, progressive loss of vision that may escape the patient's attention. In angle closure glaucoma the site from which the fluid leaves the eye is narrow or physically blocked. This can occur suddenly, which causes a painful red eye with general symptoms such as vomiting. This is due to a rapid increase in eye pressure.

The cornerstone of management of glaucoma is detecting it at the earliest possible stage. People at risk should undergo annual eye examinations. The diagnosis of the problem is made by a comprehensive eye examination with special attention in estimating eye pressure, estimating field of vision and evaluation of the eye's optic nerve and visualising the drainage angle.

The eye pressure is measured by instruments called a tonometer. This can be non-contact where a jet of air is used to estimate the pressure or contact, where the doctor uses a special instrument, which touches the eye to measure the pressure. The latter is more accurate. The upper limit of eye pressure is set at 21mm of Hg. If the pressure is more than this on three consecutive separate visits, the suspicion of glaucoma arises. At times the doctor will estimate pressure at various times of the day to confirm that the pressures are elevated.

The optic nerve is assessed by examining the back of the eye with special lenses and a microscope. Increased pressure damages the nerve fibres, which can cause excavation of the optic nerve seen clinically as cupping, signifying the cumulative damage of individual nerve fibres. These changes are now recorded with digital cameras and archived for reference at subsequent assessment to monitor progression. There are many modern instruments such as optical coherence tomogram, nerve fibre layer analyser, which can exactly quantify the glaucomatous damage to the optic nerve.

The field of vision is estimated with a perimeter. The exact site and amount of the defect is measured with computer-assisted programmes and stored for comparison overtime.

The 'triad' of increased pressure, nerve damage and the loss of fields form the syndrome of glaucoma. At times only the eye pressure is elevated without associated corresponding changes in the field of vision or nerve changes. This is known as ocular hypertension and is such that a person's eyes need careful follow up examinations. Diagnosis of glaucoma is made if at least two of these three criteria are present.

The primary aim of treatment is to preserve the existing vision for as long as possible. The typical first line of treatment is the use of eye drops, which lowers the eye pressure by helping the fluid leave the eye or by reducing the amount of fluid produced in the eye. Some people need to take different combinations of eye drops depending on the extent of damage. The drops have to be applied as prescribed by the doctor paying attention to the time schedule. The eye medications do not cure the disease. They lower the pressure to prevent further damage and therefore must be used

continuously to maintain the pressure at a level, which has been decided by the doctor, much like medications to lower blood pressure in hypertension.
In addition there are laser treatments for both open angle and angle closure glaucoma. laser trabeculoplasty is generally done for open angle glaucoma that continues to progress despite use of medications. A laser beam is directed at the outflow channels to increase the fluid drainage. The procedure is done as an out patient procedure at the eye doctor's office. Laser treatment does not cure glaucoma. It helps to lower the eye pressure, which can either stop or slow down vision loss. Laser treatment is also done for angle closure glaucoma. This is called as laser iridotomy, which is done to eliminate the mechanical blockage by diverting the fluid. A small opening is made in the iris (the coloured part of the eye). The iris falls back to open the angles thereby removing the mechanical blockage to fluid egress resulting in lowered pressure.

All laser procedures have some risks and are not done unless the benefits outweigh the risks.

Source: Weekend, 25 April 2009