Glaucoma is an eye disease characterised by damage to the optic nerve and loss of visual field. Often cases of glaucoma are related to elevated intraocular pressure (IOP), however it doesn't always have to be elevated for a person to develop glaucoma. The first line of treatment for most types of glaucoma is eye drop medication that lowers the fluid pressure inside the eye however in some cases, eye surgery may be required. Left untreated, glaucoma can lead to permanent loss of sight from the fluid pressure in the eye damaging the optic nerve. This nerve damage first affects your peripheral vision, but eventually can cause blindness.
What causes glaucoma?
The space inside the front of the eye between the cornea and the iris is called the anterior chamber. Clear fluid called aqueous flows in and out of the anterior chamber to bathe and nourish the anterior part of the eye. In one form of glaucoma, the aqueous fails to drain from the eye quickly enough, causing the pressure inside the eye to build up. Over time, the increased pressure inside the eye damages the sensitive optic nerve at the back of the eye and causes vision loss. In another form of glaucoma called "Normal Tension Glaucoma" the eye pressure never raises above the average range. However in these people the optic nerve head is exquisitely sensitive to the average eye pressure and glaucoma still eventuates.
What are the symptoms of glaucoma?
In the most common form of glaucoma (called chronic open angle glaucoma), there are no early symptoms. The eyes appear normal, vision is normal, and there is no pain or discomfort. As glaucoma progresses, peripheral vision is lost. As this form of glaucoma progresses, the visual field continues to narrow, causing tunnel vision and blindness.
There is a less common form of glaucoma called acute angle closure glaucoma. This form strikes suddenly and usually involves severe eye pain and a much quicker loss of vision.
How common is glaucoma?
Approximately 1 in 10 elderly people have glaucoma, but half are unaware of it.
Risk factors include:
- Anyone over the age of 40
- A family history of glaucoma
- Ocular trauma
- Long-term corticosteroid usage
- Medical conditions such as diabetes, low and high blood pressure, sleep apnoea and migraine
What is the treatment for glaucoma?
There is no cure for glaucoma, but it can be controlled with prompt treatment. Depending on the type and severity of the condition, glaucoma is treated in one or several of the following ways:
Medicine - Glaucoma medicines may be in the form of eye drops, pills, or both. Some medicines reduce pressure by improving aqueous drainage from the eye; others work by slowing aqueous production. Instructions on how to instil eyedrops are here.
Laser surgery - Laser surgery may be used to create wider openings in the aqueous drainage structures within the eye so the aqueous can exit the eye more easily.
Other microsurgery - Other surgical techniques may be used to increase aqueous outflow if drugs and/or laser surgery are contraindicated or cannot sufficiently reduce eye pressure. This includes a trabeculectomy and more recently Minimally Invasive Glaucoma Surgery (MIGS) such as iStents and Hydrus stents.
Reducing risk factors
There are a few modifiable risk factors that can be addressed. Recent studies have found increasing the intake of green leafy vegetables can reduce the risk of glaucoma by 20-30%. More information is here. Also raising your head while sleeping can help. Good control of sleep apnoea will help reduce the development and progression of glaucoma.
None of the treatment options for glaucoma can restore vision that has already been lost because of the disease. Treatment is intended to prevent further vision loss.
Can glaucoma be prevented?
Routine eye exams are the only way to ensure glaucoma is diagnosed before extensive damage occurs. During your exam, your optometrist will perform a test called tonometry to measure the pressure inside your eye. They will also examine the appearance of the optic nerve at the back of the eye. If glaucoma is suspected, a visual field test may be performed to evaluate your peripheral and central vision and to examine for functional loss. Early structural changes of the retina will also be investigated using a Scanning Laser Ophthalmoscope.
Retinal scanning using our the Zeiss Cirrus HD OCT is the latest technology available to allow earlier detection of glaucoma. Using a low powered laser it scans the retinal nerve fibre layer to look for structural defects characteristic of glaucoma. Often before there is a functional vision loss from glaucoma, there are structural changes to the nerve fibre layer. Our Zeiss Scanning Laser Ophthalmoscopes can detect these structural changes.
Remember that the most common form of glaucoma has no symptoms. By the
time you notice a change in your vision from glaucoma, it's too late.
See your optometrist for routine glaucoma testing to protect your eyes
from this serious sight-threatening disease.
Author: Stuart Macfarlane