Glaucoma

Glaucoma is a group of diseases that can lead to irreversible damage to the optic nerve, resulting in blindness eventually. It is one of the leading causes of blindness in adults in the world.

Loss of vision in glaucoma starts from the periphery of one's vision, and progresses towards the center of vision. In the most common form of glaucoma, there is no pain or visual symptoms at the early stages. For this reason, many affected people are unaware they have glaucoma until less than 20% of their visual field remains.

This pamphlet is designed to provide a general introduction to the nature of this eye disease, and also how it is diagnosed and treated.

2. What is the optic nerve?

The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina, the light-sensitive layer of tissue at the back of the eye, with the brain.

3. How does glaucoma damage the optic nerve?

In the front of the eye is a space called the anterior chamber. A clear fluid flows continuously into this space, and then out through a spongy meshwork at the angle (Figure 2 ). If this flow of fluid is blocked anywhere along the way, intraocular pressure builds up and damage to the optic nerve may occur (Figure 1b).


Fig 2: Segment of the eye with an open drainage angle

4. Types of Glaucoma

There are two basic forms of glaucoma, open-angle and angle-closure. The former is usually of chronic nature which comes slowly without obvious signs while the latter   is usually of acute nature which must be treated as a medical emergency.  

Primary open-angle glaucoma (POAG) gets its name because the angle that allows fluid to drain out of the anterior chamber is open (Figure 2). It is the most common form of glaucoma, and has no symptoms at first. For unknown reasons, the fluid passes too slowly through the meshwork drain. As the fluid builds up, the intraocular pressure rises. Unless the pressure is controlled, damage to the optic nerve can occur and results in visual loss.

Fig 3: A painful red eye with acute glaucoma

5. Who is at risk?

Although anyone can get glaucoma, some people are at higher risk than others. People who are at increased risk of chronic open-angle glaucoma include:

• Anyone over age 60;
• People with a family history of glaucoma – the approximate risk is 10% in siblings and 4% in offspring;
• People with high myopia;
• People with diabetes mellitus and / or hypertension.

6. What are the symptoms of glaucoma?

Those who suffer from chronic open-angle glaucoma do not have symptoms at first, and for this reason, it is often not detected until a late stage. Initially, vision remains normal, and there is neither pain nor eye redness. As glaucoma remains untreated, people may notice that although they see things clearly in front of them, they miss objects to the side and out of the corner of their eye. Without treatment, the condition progresses with time. At a later stage, it may seem as though they are looking through a tunnel (Figure 4a & 4b).Over time, the remaining central vision may decrease until vision is totally lost.

Fig 4a What a person with normal eyes will see.	Fig 4b
	What a person with advanced glaucoma might see. Because only a narrow central visual field is left, this is sometimes also known as tunnel vision.

In angle-closure glaucoma, patients may present with severe symptoms of rapid onset, such as severe eye pain, blurring of vision, headache, or even nausea and vomiting (Figure 3).

7. How is chronic open-angle glaucoma detected?

Figure 5	Fig 6a	Fig 6b
	The intraocular pressure (IOP) of the patient on the left being measured with an automated machine called a non-contact tonometer (NCT).	A puff of air is blown onto the patient's eye to detect the pressure within the eye.

Tonometry: This standard test determines the fluid pressure inside the eye. One common type is the air puff test, which measures the resistance of the eye to a puff of air (Figure 6a & 6b).

Angle assessment:Your doctor may use a special lens with built-in mirrors, called a gonioscope (Figure 7), to look at a special region within your eye, called the drainage angle&. By examining the drainage angle, your doctor would be able to say which type of glaucoma, open-angle or closed-angle, you have, and tailor the treatment regimen to your needs.	Fig 7
	The drainage angle of an eye being examined with a "gonioscope". This small optical instrument allows visualization of the angle through reflections in four small mirrors.

Fundoscopy: This examination provides your eye care professional with a better view of the optic nerve to check for signs of damage (Figure 1a and 1b). To do this, your eye care professional places drops into the eye to dilate (widen) the pupil. After the examination, your near vision may remain blurred for several hours.

Visual Field: This test measures your side (peripheral) vision. It helps your eye care professional find out if you have lost side vision, a sign of glaucoma. (Figure 8a &8b)

Figure 8a

Figure 8b

8. Can glaucoma be treated?

Yes. Although you will never be cured of glaucoma, treatment can often control it. This makes early diagnosis and treatment important to protect your eyesight.

Glaucoma treatments include oral and topical medications. Some people taking glaucoma medications may experience the following side effects:

• stinging or redness of eyes
• blurred or dimmed vision
• headache
• changes in pulse, heartbeat or breathing
• tingling of fingers and toes
• drowsiness
• loss of appetite
• change of iris color

Most side effects are not serious, and may disappear after a while. If they become serious or intolerable, you have to consult your ophthalmologist and decide if a change of medications or type of treatment is necessary.

Laser and conventional surgeries may be done after medications failed to control the IOP.

Laser surgery: In open-angle glaucoma, laser burns may be made on the drainage meshwork to decrease the resistance to fluid flow through the meshwork. This helps to open the holes and let fluid drain better through them.

Conventional surgery: An eye surgeon may remove a small piece of tissue from the white (sclera) of the eye. This creates a new channel for fluid to drain from the eye. In some patients, the new drainage opening closes and a second operation may be needed. While glaucoma surgery may save the remaining vision, it usually does not improve sight. In fact, your vision may not be as good as it was before surgery. Like any operation, glaucoma surgery may have complications. These include cataract formation, problems with the cornea, infection inside the eye and over-drainage of fluid leading to a soft eye (Figure 9)

(Figure 9)

Smoking: a threat to eye health
Age-related macular degeneration (AMD)
Cataract
Red Eye