I went to get new glasses and the optometrist told me I have glaucoma. What is this?
Glaucoma is a disease characterized by damage of the optic nerve. The optic nerve is an extension of the retinal nerve cells and it transmits the information that is received by these cells to the area of the brain responsible for vision. Glaucoma is a very slow, progressive, disease, but once the optic nerve is damaged and vision is lost, the loss is permanent and cannot be regained. It is felt that one of the factors contributing to the damage of the optic nerve is a build-up of pressure within the eye, either from overproduction, or a problem with drainage, leading to a subsequent loss of vision. Another contributing factor is ischaemia, or decreasing oxygenation, of the optic nerve. Glaucoma often produces no symptoms until it is too late and vision loss has begun.
What causes glaucoma?
The front part of the eye between the cornea and the iris is called the anterior chamber and is filled with a fluid. This fluid is constantly being produced and then drained. This produces an equilibrium within the eye, and maintains a constant pressure. This pressure can fluctuate depending on the time of day it is taken, but it tends to stay within a given range. If for some reason, too much fluid is produced, or the drainage gets blocked, there will be a build-up of intraocular pressure (IOP) within the eye. It is felt that one of the factors contributing to the damage of the optic nerve is a build-up of this IOP, leading to a subsequent loss of vision.Because the time from onset of glaucoma to blindness is a long one, the most important thing to realize is that early detection and treatment is critical.
How is it diagnosed? What tests are used?
Glaucoma is diagnosed by three main tests. These are: assessment of the optic nerve head cupping, visual field tests, and intraocular pressures.
Opthalmoscopy: this test is where the doctor uses an instrument called the ophthalmoscope to look into the back of your eye and see your optic nerve. The optic nerve should have a small central ‘cup’ where the vessels emerge. If this cup is enlarged, or irregularly shaped, this is an indication of glaucoma.
Tonometry: this test involves the use of an instrument called a tonometer which measures the pressure of the intraocular fluid within the eye. If the pressure is above the ‘normal’ range, this may indicate glaucoma. The doctor may take several measurements at different times of the day to make this determination.
Perimetry (Visual field test): this is a test that checks the function of the optic nerve, especially your peripheral vision. In glaucoma, it is the peripheral vision that goes before the central vision. It also helps to monitor progression of the disease. This is a simple computerized test where you look into a machine and press a button when you see a light. A computer then assesses your responses and gives a print-out.
But I don’t wear glasses. How can I have glaucoma?
Unfortunately, this is why so many people lose their sight from glaucoma. Glaucoma damages the visual field. If you close the left eye, everything you see with the right eye is called the visual field for that eye. Because we have two eyes with separate visual fields that overlap, you can have damage to one and not realize it because of this overlap, and this is why patients can have significant damage from glaucoma before they notice a problem. Glaucoma does not affect sharpness or clarity of vision. Thus, you can have 20/20 vision, and still have late stage glaucoma.
Can I get my vision back in that eye?
Because the time from onset of glaucoma to blindness is a long one, the most important thing to realize is that early detection and treatment is critical. If you are diagnosed in the early stages of glaucoma, you need never go blind with appropriate treatment and monitoring. The primary method of treatment is intra-occular pressure (IOP) lowering drops. You may need just 1 or 2 drops to keep your pressure at acceptable levels, or you may need as many as 4. However, if you are diagnosed when the glaucoma is far advanced, or your treatment is not sufficient, the potential for low vision or blindness exists, and the vision loss is permanent.