The silent thief of sight
Damage caused by glaucoma cannot be reversed, however, once detected, the vision loss from glaucoma can be slowed or stopped. Find out whether you are at risk.
BY: Dr Jovina See
Glaucoma is a group of eye conditions where the pressure in the eye is too high for the optic nerve and retinal nerve fibres at the back of the eye. This high pressure in the eye then causes permanent irreversible damage to the optic nerve, and leads to a narrowing of the visual field. This can result in blindness. Glaucoma can affect any age group, even newborns (congenital glaucoma). Most commonly, it affects those aged 40 years and older. In Singapore, the prevalence of glaucoma is about 3.2 percent among those aged 40 years and above.
Majority of glaucoma patients have eye pressures exceeding 21 mmHg. Patients who have a sub-type of glaucoma called “Normal Tension Glaucoma” can have glaucoma damage even when the eye pressure is in the “normal” range of below 21 mmHg. Conversely, there are also patients with ocular hypertension where their eye pressures are high but no glaucomatous damage is present at the level of the optic nerve. These latter patients have to be monitored as they can convert to glaucoma over time. Therefore, eye pressure alone cannot be used to diagnose glaucoma. A comprehensive eye examination by a glaucoma specialist, where the optic nerve is carefully evaluated, is essential in diagnosing glaucoma.
There are two main types of glaucoma: Primary Open Angle Glaucoma (POAG) and Primary Angle Closure Glaucoma (PACG). POAG is the more common type worldwide, including in Singapore. But PACG is more visually destructive, as it often involves higher eye pressures which build up more rapidly, compared to POAG. East Asians have one of the highest prevalences of PACG, including Singapore, where it accounts for more than 1/3 of all glaucoma cases. Glaucoma accounts for 40 percent of registered blindness in Singapore, with PACG contributing a higher percentage compared to POAG.
The risk factors
So what are some risk factors for developing glaucoma?
• Age is the main risk factor for glaucoma. The relative risk of having glaucoma in those above 60 years old is 9.2 times higher compared to those who are younger.
• In PACG, race is another important risk factor. Research in Singapore has shown that Chinese have a relative risk of 2.8 times that of Indians and Malays.
• Females have a relative risk of 2.4 times that of males for developing PACG.
• In some populations, up to 30 to 50 percent of glaucoma patients have at least one first degree relative with glaucoma.
• Certain eye conditions such as a dense cataract (this is when the cataract has been allowed to grow so thick with age that it starts to push the iris forward and closes the drainage angle of the eye, so that aqueous fluid in the eye cannot exit the eye. This leads to increased pressure and therefore glaucoma), previous eye trauma or eye diseases like iritis or Possner Schlossman syndrome, can also increase the likelihood of developing glaucoma. Prolonged use of medications such as steroids in the form of oral tablets, ointments/creams, or inhalers can also result in glaucoma.
Glaucoma is usually asymptomatic, hence it is often called the “silent thief of sight”. Most glaucoma sufferers do not feel any pain even when their eye pressures are high. In the early stages of glaucoma, only the peripheral visual field is blurred. Therefore, as we use our central visual field to see and do most things, we often end up missing this early symptom. By the time glaucoma is so advanced as to cause the central fields to become affected, it is already too late as the patient will by this time be quite handicapped in their daily activities. Any visual field deficit or loss of vision at this time is permanent and cannot be reversed. Hence, eye screening from the age of about 40 years old is important to discover this asymptomatic eye condition early so that damage in our vision can be prevented. If everything looks healthy on the first eye screening, and there are no risk factors or family history identified, eye screening can be done once every two to three years.
In some patients where the eye pressure rises very high (usually at least 30 to 40 mmHg), some may notice on and off mild headaches or haloes when looking at bright lights. Many mistake it for a tension headache and do not seek consultation with the ophthalmologist. In PACG, some patients may experience a one-sided headache and may mistake this to be migraine. In severe cases of PACG where the eye pressure rises to as high as 70 mmHg, patients may experience blurred vision, eye redness, nausea and vomiting. The damage to the optic nerve is usually significant and permanent in such cases.
Glaucoma is traditionally diagnosed and monitored with the help of visual field (VF) tests. However, these tests do not detect glaucoma in the early stages. Recently many new imaging devices have been invented that can help to detect glaucoma at an earlier stage, often before VF deficits manifest. These include the Heidelberg Retina Tomograph (HRT) and Optical Coherence Tomography (OCT). Both of these devices can detect glaucoma up to five to seven years earlier than the VF tests. Patients can therefore be started on treatment earlier so as to prevent any functional deficit in their vision. This way, they stand a better chance of maintaining good vision until a ripe old age. In addition to enabling diagnosis, the HRT, OCT and VF tests are also essential for monitoring the stability of the glaucoma. Regular monitoring will enable the ophthalmologist to better decide when to modify treatment.
Treatment aims towards decreasing the eye pressure to a safe level. There are three main methods – medical treatment, laser and surgery. Depending on the type and severity of the glaucoma, the glaucoma specialist determines which mode of treatment is the most suitable for the patient:
• Medical – Many different classes of medications are available for glaucoma. They work by decreasing the eye pressure to a level that is safe enough for the eye. Patients may have to use anything from one to a combination of four different types of medicines.
• Laser – Laser treatment is suitable for certain types of glaucoma. PACG in particular is often treated by laser.
• Surgery – Many types of surgery are available, depending on the type of glaucoma. Most commonly performed are trabeculectomy and glaucoma drainage implant surgery. Glaucoma surgery aims to decrease the eye pressure in order to arrest damage to the optic nerve.
Dr Jovina See is a senior consultant at Shinagawa LASIK Centre and is also the vice-president of the Glaucoma Surgeons of Singapore. She was previously head of glaucoma at the National University Hospital.