by DR. CARL STITES
Stites Eye Care
Our visual system is a complex network of nerves, blood vessels, muscles and refractive surfaces that allow us to view the world clearly. Although we have made great advancements over the years in the study of human medicine, we still cannot repair nerve fibers. If your spinal cord is severed, paralysis is unavoidable. The eye relies on nerve fibers to transmit visual information to the brain. If the nerve fibers of the eye are damaged, transmission of this visual information is affected and vision loss inevitably and irreparably occurs. This is what takes place in glaucoma. Glaucoma is the leading cause of preventable blindness in the United States.
Glaucoma is a disease of the eye that initially causes a gradual loss of peripheral vision that slowly advances to an eventual total vision loss in the affected eye. This article will deal with the most common type of glaucoma, “open angle glaucoma.”
Unfortunately, there are no symptoms-no redness, no pain and no blurred vision. Patients do not realize they have the disease, which is why it is the leading cause of preventable blindness in our country. The earliest effect of this condition is a very gradual loss of peripheral visual field. If you notice a loss in your visual field, the disease has most likely been present for quite some time and even with aggressive treatment it is often too late to save any usable vision in that eye. Any vision loss at all from glaucoma is always permanent and irreversible since it involves damage to nerve fibers. The goal in any treatment is to prevent further vision loss.
Glaucoma can affect any person at any age. I have diagnosed and treated glaucoma in 29-year-olds and 89-year-olds, although it is more common with each decade of life. There is definitely a genetic component to this disease, so if a family member is affected, your risk increases markedly. Blacks, Hispanics and diabetics are also at a greater risk of developing glaucoma earlier in life. Glaucoma has not been linked to blood pressure, diet, exercise, high cholesterol or wearing glasses.
The eyes are filled with a viscous fluid, much like a balloon is filled with air. In patients with glaucoma, the amount of fluid inside the eye increases and exerts pressure on the back of the eyeball (getting your “pressure checked” means determining the amount of fluid inside your eye). This increased fluid pressure inside the eye inhibits the heart’s ability to pump blood into the blood vessels that nourish the eye. What happens when the blood supply is cut off to any part of your body? That organ slowly loses function due to a lack of oxygen and nutrition.
A basic understanding of the eye’s structure helps in understanding the detection and treatment of glaucoma. The back surface of the eye is called the retina. The retina is a network of nerve fibers that process the images we see. All of the retinal nerves meet and connect in the back of the eye to form the optic nerve. The optic nerve is the eye’s pathway that carries visual information to the brain.
In the last 10 years, there have been fantastic advancements in diagnostic instrumentation that have helped us to detect this condition earlier and treat it more effectively. Scanning laser ophthalmoscopes, digital retinal imaging, ocular coherence tomography and newer, more accurate visual field units have ushered in a new generation of glaucoma treatment. The optic nerve is composed of over one million nerve fibers. Glaucoma eventually causes permanent damage to these nerve fibers. These new instruments allow us to detect microscopic changes to the nerves and help determine who is at risk for the disease, who is at the very early stages of the disease, and how far the disease is progressing.
The medical term for this test is non-contact tonometry (NCT). An NCT emits a small puff of air that bounces off the front of the eye and then re-enters the instrument. A computer inside the instrument measures how far the air “pressed the eyeball in” and converts it into a reading. This reading is called your “intraocular pressure.” Think in terms of how far you could press your finger into a balloon that was overfilled compared to a balloon that was half empty. When the pressure inside the eye starts to increase over time, the patient is monitored more closely for changes to the nerve fibers of the eye that would indicate glaucoma.
Another method of measuring intraocular pressure involves instilling a yellow dye into the eye and using a purple light to determine the pressure reading. This is called Goldman tonometry.
When caught early, the treatment is very simple: eye drops. These drops are not a cure for the disease; they basically lower the intraocular pressure inside the eye to prevent vision loss. Medication needs to be taken for the rest of your life to preserve your vision.
Newer, more effective medications have been discovered in the last 10 to 20 years. The older generation of drugs caused frustrating side effects and had a shorter duration of action. The newer generation of glaucoma medications is often taken only once daily, is very effective at controlling the disease, and has minimal side effects.
Surgical options are available in certain instances. Surgery is often a last resort to try to save any usable vision in advanced stages of the disease or in patients who are unresponsive to topical medications.
The eyes are the portal through which we absorb the world. Seventy percent of the information we take in every day is through our vision. The single most important factor in preventing vision loss from this sight-robbing malady is early detection during annual ocular health evaluations. Yearly exams by a qualified professional using the latest diagnostic instrumentation are imperative to keeping the eyes in good health.
I often hear people say, “I don’t need to get my eyes checked. My vision is perfect!” Well, that may be the case, but I only spend about 25 percent of each patient’s examination determining a prescription for glasses. The vast majority of each visit is spent assessing the health of the eyes-it is the most important thing I do. Every patient I have ever diagnosed with glaucoma was truly shocked that they had the disease. They will often say, “I had no idea. I didn’t notice a thing,” which is why glaucoma is the leading cause of preventable blindness in the United States. Your eyesight is truly a gift that cannot be replaced.