SINGAPORE: Glaucoma is an eye condition that can cause progressive loss of vision due to damage to the optic nerve. The optic nerve carries what you see from the eye to the brain, therefore damage to the nerve will result in damage to your sight. Usually, but not always, the damage occurs because pressure within the eye increases.

According to Associate Professor Aung Tin, who is senior consultant and head of Glaucoma Service (Research Development) at the Singapore National Eye Centre, glaucoma is one of the world’s leading causes of irreversible blindness. In Singapore, approximately three per cent of people over the age of 50 years have glaucoma. This percentage increases with age, with almost ten per cent of people over the age of 70 years suffering from this condition.

“It has been shown worldwide that over 90 per cent of people suffering from glaucoma are unaware of it because of the lack of symptoms. For this reason, it is sometimes called the “silent thief of sight”. Glaucoma is not curable, but blindness is preventable if glaucoma is diagnosed and treated early enough. While usually there are no warning signs, regular eye tests will detect the onset of the disease,” advised Associate Professor Aung.

Types of glaucoma

Glaucoma occurs in several types, and the signs and symptoms vary depending on the type of glaucoma you have.

Open angle glaucoma progresses with few or no symptoms until the condition reaches an advanced stage. As increased eye pressure continues to damage your optic nerve, you lose more and more of your peripheral (side) vision. If left untreated, you can develop tunnel vision and eventually lose all sight. Open angle glaucoma usually affects both eyes, although at first you may suffer vision loss in just one eye.

“Open angle glaucoma cannot be prevented but if diagnosed and treated early, it is possible to prevent visual damage and blindness,” said Associate Professor Aung.

Closed angle glaucoma, however, may be potentially preventable. In the early stages of the disease (when the eye has a closed angle but has not developed glaucoma yet), performing a laser procedure called laser iridotomy can prevent blindness caused by closed angle glaucoma. The procedure involves using laser energy to create a hole in the iris (the brown part of the eye), causing the angle to become “wider”. This treatment ‘ ophthalmic vaccination ’ is a low-risk procedure.

Family history a risk factor

Glaucoma has a strong genetic basis. Family history is a very important risk factor for glaucoma. Studies have shown that up to 50 per cent of primary open angle glaucoma patients report a family history of glaucoma.

First-degree relatives of patients (parents, siblings and children) with glaucoma are at increased risk for the disease. The exact risk is difficult to determine but these are estimates:

* If you have a sibling with glaucoma, you will have three to five times higher risk for glaucoma (the risk to siblings is about ten to 20 per cent chance).

* If you have a parent with glaucoma, you will have two to three times higher risk for glaucoma (the risk to offspring is about four to five per cent chance).

Associate Professor Aung added: “Therefore, if you have glaucoma, it is important that you inform your relatives, so that they are aware. It is also important to encourage your relatives to have regular eye checks. This is particularly critical for first-degree relatives over the age of 40 years.”

Individuals with a family history of glaucoma in first-degree relatives should be examined by an ophthalmologist from the age of 40 years. Provided the initial assessment is normal, subsequent reviews should be done every two or three years until the age of 50 years and then annually thereafter.

Other risk factors include:

* Age: Age is a large risk factor in the development of glaucoma. Everyone older than the age of 60 years is at increased risk of the disease. For blacks, however, the increase in risk becomes apparent earlier, after the age of 40 years.

* Race: Blacks are significantly more likely to get glaucoma than are whites, and they are much more likely to suffer permanent blindness as a result. Mexican-Americans also face an increased risk. Asian-Americans are at higher risk of angle-closure glaucoma, and Japanese-Americans are more prone to low-tension glaucoma. The reasons for these differences are not clear.

* Medical conditions: Diabetes increases your risk of developing glaucoma. A history of high blood pressure or heart disease also can increase your risk, as can hypothyroidism.

Routine consumption of coffee has recently been found to be associated with a slight increase in intra-ocular pressure.

* Refractive error: Short sightedness or myopia is a risk factor for open angle glaucoma, while long-sightedness or hyperopia is a risk factor for closed angle glaucoma.

Singapore National Eye Centre is an institution of SingHealth, the largest integrated healthcare group in Singapore.