Glaucoma

Glaucoma is an eye condition where damage to the optic nerve results in the gradual loss of vision. The optic nerve in each eye serves to transmit images from our retina to our brain. Usually, but not always, damage to the optic nerve in is caused by high pressure within the eyeball.

Sometimes called the "silent thief of vision", Glaucoma often causes irreversible harm to the eyes before there is any vision loss. Without treatment, glaucoma can lead to blindness.

In Singapore, Glaucoma affects about 3 per cent of those aged over 40. This risk increases with age.

The eye is like a ball filled with fluid which provides oxygen and nourishment to the rest of the eye. It has an inflow tap (ciliary body) and an outflow drain (trabecular meshwork).

To maintain normal pressures, the inflow must balance the outflow. In certain types of Glaucoma, such as Angle Closure Glaucoma, if the drainage is blocked, fluid accumulates and pressure in the eye builds up. This raised pressure may damage the optic nerve.

Glaucoma can be classified into primary (not associated with other eye diseases) and secondary (as a result of pre-existing eye diseases). These are sub-divided into Open-Angles and Closed-Angles Glaucoma.

Primary Open-Angle Glaucoma

This is the most common type of Glaucoma. Its symptoms are usually gradual and you may not notice any vision loss until the advanced stages. Primary Angle-Closure Glaucoma may be be acute or chronic.

Acute Primary Angle-Closure Glaucoma

• Occurs more commonly in the middle-aged or elderly, especially those who are long-sighted.
• Characterised by a sudden increase in the eyeball pressure, causing sudden onset of pain, redness and blurred vision in one or both eyes. There may be headache, nausea and vomiting as well.
• Urgent treatment to lower the pressure is essential to save vision.

Chronic Primary Angle-closure Glaucoma

• Vision loss is progressive with side vision usually being affected first.
• The disease is often very advanced before visual loss is noted, that is why this disease is often called the "silent thief of vision".

In both forms of Glaucoma, laser treatment (peripheral iridotomy), along with anti-Glaucoma eye drops may be needed.

Secondary Glaucoma occurs when other eye diseases cause an increase in eye pressure, leading to optic nerve damage. This can be related to other medical conditions such as diabetes mellitus, or can happen following injury to the eye.

One can also be born with Glaucoma, in the case of Congenital Glaucoma.

Normal Tension Glaucoma

In Normal-Tension Glaucoma, susceptible individuals develop optic nerve damage even when their eye pressures are within normal limits.

Risk factors for the development of Normal-Tension Glaucoma include:

• Family history of Glaucoma
• History of major blood loss or blood transfusion
• History of migraine
• History of Raynaud's phenomenon- spasm of blood vessels leading to discolouration of fingers and toes.

Treatment with anti-Glaucoma eye drops is first line for this condition.

In Open-Angle Glaucoma and Chronic Angle-Closure Glaucoma, you may not notice any vision loss until it is in its advanced stage. Vision loss is gradual, with side vision typically being affected first. As the condition progresses, the vision (visual fields) gets increasingly narrower and eventually only a small central island of vision is left and you will only be able to see what is directly ahead of you.

In Acute Angle-Closure Glaucoma, symptoms are typically more sudden and severe. You may notice/experience the following:

• Blurring of vision
• Eye redness
• Eye pain, often associated with headache
• Nausea and vomiting

If you experience any of the symptoms, please visit your ophthalmologist immediately.

Early treatment is essential to prevent further vision loss.

The diagnosis of Glaucoma will be made by your eye doctor following a comprehensive eye examination and review of investigations.

You may undergo the following tests / investigations:

• Tonometry is the diagnostic test that measures the pressure inside your eye, called the intraocular pressure (IOP).
• Your eye pressure can be measured using instruments such as non-contact tonometer (commonly known as "air puff") or the tono-pen.

Normal Eye Pressure

Our normal pressure can range from 10 to 25 mmHg, and this can vary throughout the day. In general, doctors are more concerned with whether your current eye pressure is sufficiently low to slow down or prevent Glaucoma damage to your eyes.

If the pressure is more than 21 mmHg, as checked by your doctor or optometrist, you should consult an eye specialist. The eye specialist or ophthalmologist can accurately determine if your eye pressure is normal, or is high and associated with Glaucoma. Your eye pressure will be checked at each visit and its trend and in particular, its progression, will be monitored by your eye doctor.

One of the instruments used in measuring eye pressure

• Gonioscopy is done by your eye doctor to determine if your Glaucoma is of the "open-angle" type or the "angle-closure" type.
• Anaesthetic eye drops will be given prior to placement of a special lens/mirror on your cornea. This examination is quick and painless

• This takes about 15 minutes and is usually carried out in a dark room.
• You will be asked to look at a central light source on a white screen. Flashes of light of different intensities and sizes will appear on the screen and you will be required to press a button when you see them.
• This assesses the degree of optic nerve damage and measures the extent to which each eye can see on either side of an object.

• This is done by your eye doctor who will look at the back of the eye through a special lens to assess the health of the optic nerve.
• Photographs and specialised scans of the optic nerve may also be taken to help your eye doctor assess the degree of nerve damage, if any.

Normal optic disc

Optic disc in a patient with Glaucoma

Glaucoma is a potentially blinding condition. However, its progression is usually gradual. If it is detected early, and one complies to treatment and follow-ups, the risk of blindness can be reduced. If diagnosed early, we can treat Glaucoma and prevent blindness in most cases.

Management of Glaucoma depends on the type of Glaucoma, degree of optic nerve damage, your eye pressure, the presence of other eye problems and your age.

Eye drops are the most common form of treatment used to reduce eye pressure. Compliance with your eye drop regime is of utmost importance in ensuring success of your medical therapy.

Some of the eye drops have side-effects, as the drops are absorbed into the bloodstream. This absorption can be minimised by pressing a finger against the lower lid where it meets your nose, or by closing your eye for one minute after instilling the eye drop. Any side effects should be reported to your doctor. It is important that if there is more than one Glaucoma eye drop, to instill them at least five minutes apart.

Compliance with anti-Glaucoma eye drops, together with regular follow-ups with your eye doctor, is key to prevent your glaucoma from getting worse.

Instillation of eye drops

This is usually done if medical therapy and anti-Glaucoma eye drops fail. The most common surgery is trabeculectomy, where an opening is created for the fluid in the eye to escape into the surrounding tissues and absorbed. This allows the pressure inside the eye to be relieved.

Other kinds of surgery are available and include inserting a tube to drain the fluid from the eye. This is often indicated in complicated Glaucoma.

This is usually carried out in patients with angle-closure Glaucoma (laser peripheral iridotomy) or in patients with acutely high eye pressure not responding to medical treatment (laser peripheral iridoplasty).

It is important to tell your eye doctor if you have the following conditions/ drug allergies as it may affect the type of treatment given:

• Any form of drug allergies - especially sulphur allergy
• Kidney disease
• Heart disease - especially heart block and heart failure
• Asthma

If you have Glaucoma, you may continue with your usual activities and diet. If you are on steroids, please inform your eye doctor as this may sometimes contribute and lead to progression of your Glaucoma.