What is Glaucoma?
Glaucoma is a wasting disease of the optic nerve. This causes progressive vision loss, starting un-noticed in the surround (peripheral) vision and causing noticeable patches of vision loss and sometimes blindness later in the disease.
Who gets glaucoma?
About 1-2% of New Zealanders have glaucoma. But the proportion of people affected increases with age. One in ten New Zealanders over the age of 80 has glaucoma. Glaucoma is caused by the combination of genes you carry. The inheritance is unpredictable but if you have a first-degree relative with glaucoma your chances of having the disease yourself are increased 25%. A first-degree relative is a mother, father, brother or sister. It is very important to pass on information on this condition to others in your family as it may help with early detection. So, in summary, a cocktail of genes and aging causes glaucoma.
How is glaucoma detected?
There are several tests necessary to diagnose and monitor glaucoma. These include measuring the pressure in the eyes, examining the optic nerves and mapping the sensitivity of the surround vision with special automated visual field testing. These tests will be repeated on a regular basis to monitor and manage the glaucoma.
Optometrists are often the first to diagnose glaucoma. This is because the need for spectacles increases with aging and optometrists are alert to the disease and screen for it.
Spectral domain OCT scanning
With the advent of spectral domain OCT scanning (SDOCT), Eye Doctors have a powerful modern tool for measuring the amount of optic nerve tissue in each eye directly. The SDOCT retinal nerve fibre analysis is recommended as an annual test, especially for those at risk of glaucoma or those with early stage disease. It can accurately detect loss of nerve tissue from glaucoma before this is manifest in the visual field test. The tests used to monitor glaucoma are covered by Southern Cross.
Corneal thickness measurements
Ultrasound measurement of the thickness of the cornea should be undertaken on all glaucoma patients and those at risk of glaucoma. The observed intraocular pressure is adjusted on the basis of the corneal thickness and furthermore the corneal thickness is an independent predictor of glaucoma and glaucoma severity. For example those with thick corneas have higher intraocular pressure even though they may not have glaucoma and those with thin cornea may have a seemingly normal intraocular pressure which when adjusted upwards gives the true picture and explains the presence of the disease.
Due to statistics compiled from large US studies it is possible to assign a probability of getting glaucoma to a patient in some instances. On the basis of this probability treatment may be instituted prior to the development of glaucoma. The benefit is a delay in the onset of glaucoma. The downside is possibly using drops un-necessarily.
Visual Field Test
Patients with glaucoma require long term follow up. During the period of follow up it is most important to know whether the glaucoma is getting worse. Regular visual field tests tells if the vision is getting worse. A visual field test is a map of the surround vision of each eye. Usually visual field tests are made every year but if the glaucoma is severe more frequent field tests may be required.
There is no doubt that lowering the eye pressure slows the progression of glaucoma. The usual way of lowering the eye pressure is by instilling pressure lowering eye drops on a daily basis.
Depending on the type and severity of the glaucoma there are other options for treatment.
Angle closure glaucoma
This is a common type of glaucoma that affects long-sighted people and Asians. Long-sighted people have smaller eyes than others. Long-sighted people never needed glasses when they were young but had to get glasses for reading in their forties. The lens in the eye grows as a person matures. The increase in size of the lens may cause pressure on the eye’s plumbing in particularly in people with small eyes. Such people are helped by a safe laser procedure called a peripheral iridotomy, which provides a way of bypassing this type of plumbing congestion.
Laser Trabeculoplasty: This is a laser method of reducing the intraocular pressure by exposing the trabecular meshwork to laser. The trabecular meshwork is the name given to the eye’s internal gutter that drains eye fluid away from the eye.
Surgery may be necessary for treating glaucoma. The surgical procedures that are employed for treating glaucoma are as follows:
Cataract surgery: This can reduce the pressure by freeing up the plumbing of the eye. It is especially useful in those long-sighted patients with small eyeballs and large lenses. The mature tissue lens is removed and replaced with a much smaller plastic lens. Immediately following successful cataract surgery there is much more room inside the eye to provide for the uninterrupted drainage of eye-fluid.
Trabeculectomy surgery: A small, gated hole is made in the sidewall of the eye to permit the drainage of eye fluid directly from the eye into a space between the skin of the eye (conjunctiva) and the wall of the eye.
Tube surgery: A silicone tube is placed within the eye to allow for the drainage of fluid away from the eye to be absorbed back into the body from the space between that wall of the eye and the skin of the eye.
Cyclodiode laser: In very serious cases the tissue within the eye that makes the eye-fluid can be destroyed by infrared laser light directed straight through the wall of the eye.
iStent surgery: Currently the smallest implant used in medicine, the Glaukos iStent is a 2mm titanium snorkel that creates an exit passage for blocked eye fluid, relieving the pressure that causes glaucoma. The iStent is not only effective but it has also dramatically reduced recovery time following surgery.