Resolving the Mystery of Glaucoma
This article appeared in the Pontiac Daily Leader and Fairbury Blade in September 2014. By Sasha L Radford, OD
When asked about family history of eye disease, patients often confuse glaucoma with other conditions. “I think my grandmother had glaucoma, but she had surgery and got implants for that” (likely cataracts). Or, “My dad takes vitamins for that” (probably macular degeneration). If, on the other hand, a patient tells me a family member uses eye drops full time for an eye condition, glaucoma is a good possibility. Glaucoma is a mystery to patients and sometimes even doctors, for many reasons.
Glaucoma is a disease of the optic nerve, the structure in the back of the eye which carries visual signals to the brain. In glaucoma, these nerve fibers become damaged resulting in peripheral vision loss. It is more common in older patients but can occur at any age; family history is a risk factor as well. Glaucoma has no cure but is very treatable once detected. Usually eye drops are all that is needed to stop the damage to the optic nerve but there are also laser and other surgical procedures that can be performed when eye drops are not effective.
One reason glaucoma is so mysterious to patients is that there are usually no symptoms until quite late in the disease. Vision loss occurs very slowly and most have no pain or discomfort at all. In the early stage of glaucoma, loss occurs slowly in the peripheral vision; a small area of loss in one eye may be easily overlooked due to the intact vision of the other eye. If left untreated, these small defects in the periphery gradually enlarge, leading to tunnel vision and finally loss of central vision.
Glaucoma is often elusive to doctors as well, because there is not a single definitive test. Diagnosing glaucoma is like assembling a puzzle – there are several tests that must be fit together just right to come up with the correct diagnosis and treatment plan.
In most instances of glaucoma, the fluid pressure inside the eye is higher than normal, but this is not always the case. Most people associate the eye pressure test with glaucoma, but in fact it is only a small piece of the puzzle.
Patients with glaucoma typically present with a certain appearance of the optic nerve, but size, shape, and features of optic nerves is highly variable and what may be abnormal for one patient could be a normal variation in another.
The visual field test is performed when glaucoma is detected: small spots of light of varying brightness are presented to the patient in different locations; the patient must push a button each time he perceives the light. This serves to map the sensitivity of the peripheral vision – certain patterns of defects in a visual field are indicative of glaucoma. However, visual field testing is lengthy, difficult for patients to perform, and highly variable. Typically the test must be repeated two or three times before the results can be trusted to be accurate. In addition, many other conditions can cause visual field defects, so those must be ruled out as well.
Another test we use to detect glaucoma is optical coherence tomography (OCT) which measures the thickness or volume of optic nerve fibers. The test is more valuable in that is quick and requires no response from the patient. Results are compared to a standard set of normal values and repeated periodically to check for changes.
In fact, the most important element of diagnosing glaucoma is detecting a change over time, whether it be a change in optic nerve anatomy, thickness of nerve fibers, peripheral vision loss, or a combination of any of these. While the battery of testing can be tedious and time consuming, making the correct diagnosis is important.
Treatment is much more effective when begun early, before vision loss has occurred. The optimum time for treating glaucoma is before the patient is ever aware there is a problem – no pain, no noticeable vision loss. This is one of the many reasons why comprehensive eye examinations are so important to maintain the good vision that you have.