Wednesday July 15, 2009
Loss of sight
By MAJORIE CHIEW
Blindness can creep up almost unnoticed in the aged who suffer from glaucoma.
GLAUCOMA is often called “the sneak thief of sight” because in most cases, sufferers will gradually lose sight without any symptoms.
The majority of glaucoma cases in Malaysia involve the elderly, who often associate blurring of vision to cataracts (the clouding of the lens in the eye), says Dr Shamala Ganesan, a cornea specialist and ophthalmologic surgeon.
“These people wait until they can’t see light or can only see hand movements before seeking medical help. If they have cataracts, it’s just the removal of the opaque lens. If they have glaucoma, it may be at the terminal stage where 90% of the optic nerve has been wiped out. Treatment may not be so successful and the patient may end up losing his vision.”
Normal eye with healthy normal nerve fibre rim and normal cup to disc ratio. The optic nerve receives light from the retina and transmits impulses to the brain that we perceive as vision. Glaucoma is a condition of progressive visual loss which can lead to blindness as a result of the optic nerve damage. It begins with a subtle loss of side vision (peripheral vision) and if not diagnosed and treated, it can lead to loss of central vision and blindness.
In general, the majority of people with glaucoma in Malaysia have “silent loss of vision” because the intra-ocular pressure builds up and destroys sight without symptoms.
Elevated eye pressure can lead to damage of the eye optic nerves. In some cases, glaucoma may occur in the presence of normal eye pressure as a result of poor regulation of blood flow to the optic nerve. The gradual death of the optic nerve is irreversible and leads to blindness.
According to the World Health Organisation (WHO), about 60.5 million people will have glaucoma by next year. With the world population ageing, the number may increase to 80 million by 2020.
An eye with glaucoma with a thin nerve fibre rim, especially above and below. Note the plunging blood vessel as it enters the optic nerve. WHO also found glaucoma to be the second most common cause of blindness worldwide, after cataract. It is estimated that 4.5 million people have been blinded by glaucoma and this number will rise to 11.2 million by 2020.
Shamala cites that the majority of those with glaucoma are the elderly and the average age is 62 years. The prevalence of glaucoma is 54.8% in the male population compared with 44.6% in the female population. With increasing aged population and life expectancy, more people will be affected with glaucoma. Findings from the 1996 National Eye Survey showed that 1.8% of those who were blind or had low vision was due to glaucoma.
“Glaucoma is unlike cataract where vision starts to drop (blurring occurs),” says Shamala. In glaucoma, the vision is still very clear but it starts to tunnel (becoming narrow).”
A person can see the television and read the book sharply. But in the dark room, the person may trip over steps because his vision is tunnelled. Or when driving the car, he may not noticed the pedestrian or car on the left side and frequently gets involved in accidents.
Those at risk
While everyone is at risk for glaucoma, certain people are more vulnerable and thus, require frequent eye checks. The major risk factors include: those aged 50 years and above, family history of glaucoma, race and history of elevated intra-ocular pressure. Medical problems like diabetes, hypertension and high cholesterol also raise the risk of glaucoma, as do short-sightedness and smoking. Trauma or history of injury to the eye can induce an ongoing glaucoma.
In advanced stages of diabetes, many new blood vessels grow in the back and front of the eye. These form a membrane which block the flow of aqueous fluid. Pressure goes up and damages the eye.
Cataracts can be one of the causes of glaucoma. “It usually happens in patients who keep their cataracts until it over-ripens and starts to melt down. The lens’ protein gets into the canal that drains out the aqueous fluid and blocks it,” says Shamala. Treatment can be very difficult from people who develop glaucoma from cataracts and many patients eventually lose sight, she says.
Patients often wait too long before seeking treatment says cornea specialist and ophthalmologic surgeon Dr Shamala Ganesan. The common types of glaucoma among Malaysians are the angle closure glaucoma (also known as acute glaucoma or narrow angle glaucoma) and primary open angle glaucoma.
“Primary open angle glaucoma is a silent thief of vision. The pressure rises (because the fluid can’t drain out of the eye as a result of clogging inside the drainage canals) so gradually that there is no pain but tunnelling of vision,” says Shamala.
In angle closure glaucoma, eye pressure rises quickly and the drainage canals get blocked. Symptoms include eye pain, headache, nausea, halos and blurring of vision. This type of glaucoma is more common in people with a shorter eyeball (particularly old Chinese women). These sufferers will complain of a brow headache (slight pain around the eyes) after prolonged watching of a movie or television.
“However, there will come a day where they will get acute attacks such as severe headache, painful eyes, nausea, severe vomiting and blurred vision.
Paediatric glaucoma can arise from birth when there is malformation in the outflow canal. These patients need surgery, she says.
Glaucoma is hereditary. Shamala informs that if your parents have it, there is a chance of one in two that you would have it.
“But if your sibling has it and your parents don’t, there is a one-in-four chance. But if your first cousin (your relative) has it, there is a one-in-eight chance (that you would have it).”
Hence, it is always advisable to screen for glaucoma and the best age for screening is at 30.
Detection and treatment
Awareness and early detection of glaucoma is extremely important. Through regular eye exams (once every two years or more often for those at risk), glaucoma can often be detected in its earliest stages and successfully treated. Such exams can help prevent damage to one’s vision.
An ophthalmologist can usually detect those individuals who are at risk for glaucoma (because of a narrow filtering angle or increased intra-ocular pressure) before nerve damage occurs. Diagnosis of patients who already have glaucoma can be done by observing their nerve damage or visual field loss through several tests.
Glaucoma is treatable but not curable. Treatment is a lifelong process. “In adult glaucoma, the mainstay of treatment is still eye drops,” says Shamala.
“The eye drops are to control eye pressure and reduce it to a level that does not cause progression of nerve damage. However, this progression varies in individuals: it can be very slow, fluctuates or very rapid (within two years, there is loss of vision).”
Shamala concedes that “the difficult part about treating glaucoma is that the cause is multifactorial; it is not due to one cause only.” Surgery is the last option in cases where the progression is not so rapid.
In cases where progression is very rapid, surgery should be immediate. If surgery is successful, the eye pressure is sustained at a low level at all times.
Secondary glaucoma (caused by like trauma, cataracts and diabetes) is more difficult to treat and more progressive than primary glaucoma. This sort of glaucoma is recalcitrant to eye drops and needs surgery.
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