What is Glaucoma?

I have come to realise that glaucoma is a very poorly understood condition. Most people have heard of the disease, but few understand what it really is and how it can affect them. In this article, I will attempt to explain what glaucoma is.

Glaucoma is actually a disease affecting the optic nerve of the eye. Images are perceived by the retina and carried via the optic nerve to the brain, where they are interpreted. Hence, the optic nerve is a very important structure, and its health is critical to having good vision.

eyeball
Glaucoma results in damage to the Optic Nerve, which connects the Eye to the Brain. Without a healthy Optic Nerve, we cannot have good vision.

In glaucoma, the optic nerve is progressively damaged, and this affects both its structure and function. Structural damage of the nerve can be seen by an Ophthalmologist using special instruments to visualise the inside of the eye. Structural damage can also be measured objectively with specialised tests that can be done in an Ophthalmologist’s clinic.

glaucoma-nerve-changes
Structural damage to the Optic Nerve results in what is known as cupping of the nerve, where its edges are thinned out like the rim of a cup.

Functional damage to the nerve typically results in a loss of ones’ peripheral vision, which can progress from mild loss to tunnel vision. Interestingly, although peripheral vision is very important, mild losses are usually not noticed by patients. For example, when I see something out of the corner of my eye (such as a car on the road), my instinct is to turn my head in the direction of the car, thereby bringing it into my central field of vision. Hence, if my peripheral vision is poor, I may not initially realise it.

glaucomavision
Here’s an illustration I found that shows what tunnel vision is. 

The cause of the optic nerve damage is frequently (but not always) raised eyeball pressure, and hence the strategy to treat glaucoma involves lowering the eyeball pressure. This is usually achieved with medications, but may also involve laser treatment or surgery.

Here’s one fact that is quite frightening- most cases of glaucoma have no symptoms! Normal eyeball pressure is about 21mmHg, and contrary to popular belief, eyeball pressure can be raised without pain or other symptoms. A patient usually only feels eye pain when eyeball pressure is very significantly elevated. Unfortunately, in most cases, eyeball pressure is raised but not to the extent that it causes pain, and optic nerve damage goes undetected until late stage disease. Patients sometimes present with only tunnel vision remaining, and because optic nerve damage cannot be reversed, there is no way to restore their peripheral vision once lost.

How do we know that we do not have glaucoma? Since glaucoma has no symptoms, the only way to know for sure is to see an eye care professional for eye screening. Annual eye screening is recommended for anyone over the age of 40, to detect eye conditions such as cataract and glaucoma.

I hope this gives you a better understanding of what glaucoma is! There are actually many types of glaucoma, and many different types of treatment, which I will share in subsequent posts.