Angle Closure Glaucoma

angle closure
In angle closure, fluid in the eye is unable to drain from the trabecular meshwork, resulting in the build up of eye pressure

 

The front of the eyeball is filled with a colourless fluid, known as aqueous humour. It is continually being produced in the eye and drained from the eye, through a drainage channel in the eye called the trabecular meshwork. In some patients, the part of the eye where the trabecular meshwork is located (known as the angle) is narrow, which can reduce the drainage of fluid from the eye. When pressure builds up in the eye as a result of this, angle closure glaucoma results.

Pressure build up can occur acutely, and can build up to very high levels. This results in symptoms of eye pain, redness, blurred vision and headache. The patient may also experience nausea and vomiting.

APAC
The red, painful eye of acute angle closure glaucoma

Angle closure glaucoma is an emergency. When the eye pressure is dangerously high, the optic nerve located at the back of the eye can become damaged. This damage is permanent and irreversible, and the patient can permanently lose vision as a result.

How is this condition treated? In the acute situation, the priority is to lower the eye pressure as quickly as possible, to reduce the damage to the nerve. This is achieved using medications, which are administered as eyedrops, oral pills or even injections.

Once pressure is controlled, laser treatment is performed to create an alternative channel for fluid to flow, and prevent the build up of pressure from occurring again.

PI.jpg
Laser treatment has been performed in this eye, creating an alternative channel for fluid to flow and preventing acute pressure rise from recurring

Patients with this condition sometimes suffer damage to the trabecular meshwork as a result of the high pressure, which results in chronic angle closure glaucoma. These patients often require life long treatment with anti glaucoma eyedrop medications.

Eye pain and redness are symptoms that should never be ignored, especially if they are accompanied by headache and vomiting. If you ever experience these symptoms, consult an Eye doctor without delay.

 

Open Angle Glaucoma

In Singapore, the overall prevalence of glaucoma is 4%- meaning that in your lifetime, you have a 4% chance of developing glaucoma. Not a big number- the odds are still in your favour, but it is still a condition worth knowing about.

Open angle glaucoma accounts for nearly half of glaucoma in Singapore- 1.7% of the population have or will have this disease. That figure does not sound intimidating. What is worrisome is that this disease does not have many symptoms, and many patients are diagnosed late for this reason.

In open angle glaucoma, the optic nerve at the back of the eye undergoes progressive damage. This is most often (but not always!) due to high eyeball pressure. Contrary to popular belief, this rarely causes pain or discomfort to the eye, and the patient is often unaware that he has glaucoma.

The result of optic nerve damage is visual field loss- reduction in the patient’s peripheral vision. Peripheral vision is important in daily life- it allows us to safely cross roads or drive, for example, but early peripheral vision loss is usually not noticeable. A loss of central vision is noticed by patients immediately, but loss of peripheral vision is much more subtle and can progress to severe loss before it is perceived by the patient.

As a result, open angle glaucoma is often diagnosed late, when significant peripheral field loss has occurred. Occasionally patients present when only tunnel vision remains, or worse, when the peripheral field is completely lost and the disease starts to affect central vision.

How is open angle glaucoma diagnosed? When patients present to an Ophthalmologist, a detailed history and physical examination is performed. Intraocular pressure is measured- usually raised beyond 21mmHg in the case of open angle glaucoma. Signs that point to the disease- a characteristic weak, thinned-out appearance of the optic nerve, would make one suspicious of the disease. The disease is often confirmed on further testing, where both structure and function of the nerve is tested. High resolution Optical Coherence Tomography (OCT) scans of the optic disc and the surrounding nerve fibre layer can determine if there is any thinning of the nerve due to glaucoma, and Humphrey Visual Field (HVF) testing can map out areas of visual field loss.

 

High resolution OCT image showing significant nerve fibre layer thinning. The red areas in all the circular plots are abnormal.

How is open angle glaucoma treated? Several eyedrop medications exist that can be instilled to lower intraocular pressure and reduce the progression of nerve damage. If eyedrops are insufficient to treat the disease, laser procedures and surgery can also be done to manage the disease.

If you are over the age of 40, or have a family member who has glaucoma, it is a good idea to go for a comprehensive eye screening to ensure that you do not have this problem.

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.