What is Glaucoma?
Glaucoma is a multifactorial ocular disease in which the optic nerve is damaged over time. The optic nerve is located in the back of the eye. The nerve fibers in the retina collect at the optic nerve and the optic nerve carries the vision impulse to the vision center in the back portion of the brain. The major contributing factor in damage in glaucoma is the intraocular pressure. In most cases the intraocular pressure is elevated. It is believed that the elevated eye pressure diminishes the blood flow in the head of the optic nerve. There are cases where the intraocular pressure is not elevated but the patient still gets damage to their optic nerve. This is called normal pressure or low tension glaucoma.
Vision Loss Caused by Glaucoma
In the most common type of glaucoma called open angle, there are no visual symptoms until late in the disease. Open angle comprises more than ninety percent of glaucoma cases. You may have to lose more than fifty percent of the optic nerve fibers in the nerve before any vision loss can be detected. There seems to be a little bit of a safety margin present in the optic nerve.
When vision loss starts to occur, it is very subtle. In most cases, it does not blur the vision until the end. There is a slow insidious loss of the peripheral vision over weeks, months, or years depending on the level of the intraocular pressure. The side vision loss is so slow and subtle that very few people are able to pick it up on their own. The eye doctor uses a computerized visual field machine that measures the side vision to a fine level. Also our brains tend to compensate for the side vision loss and we either turn our heads more or move our eyes more to see to the side.
The diagnosis of glaucoma is made by an eye doctor examining the eye and using several different tests.
The eye doctor measures the eye pressure using one of several methods. The normal eye pressure is 10 to 21 mmHg.
Optic Nerve Damage
The eye doctor examines the appearance of the optic nerve and records the cup-to-disc ration. The amount of opening in the nerve compared to the amount of nerve tissue present in the optic nerve.
This instrument measures the side vision. You are placed in a bowel-like machine with one eye patched and a series of lights are shown. Every time you see the light, you push a button to acknowledge seeing the light. The visual field computer records your response. Glaucoma damage or the vision loss has a typical appearance which is recorded.
OCT or Optical Coherence Tomography
The computerized scanning device measures the thickness of the nerve fiber layer just before it enters the optic nerve. It is able to detect early loss of nerve tissue related to glaucoma damage.
Glaucoma Treatment Goals
Once the data is collected and the diagnosis of glaucoma has been made or the eye doctor has made a determination that damage is going to occur, a treatment protocol is started. Based on the information obtained a target pressure or the pressure the eye doctor feels is a safe level is chosen. The target pressure is based on how high the intraocular pressure is and the severity of the damage to the eye from glaucoma.
In eyes that have minimal glaucoma damage or no glaucoma damage but the eye doctor is concerned about the level of the intraocular pressure, reducing the eye pressure to the upper level of normal may be adequate.
In eyes where the eye is totally normal but the eye pressure is only slightly elevated, no treatment may be necessary. These patients may need close monitoring and no treatment.
In eyes where significant glaucoma damage is present or in patients with normal pressure glaucoma, the target pressure may need to be in the 10 to 12 mmHg range.
Glaucoma is treated with several different topical ocular medications, laser treatment with Selective Laser Trabeculoplasty (SLT) or Argon Laser Trabeculoplasty, and/or a variety of surgical procedures. Most cases of glaucoma can be controlled with medication and laser treatment.
Glaucoma occurs in approximately 1 to 2 % of the population in the United States. In most cases, glaucoma does not cause any symptoms until it has advanced considerably. There is a major component of genetics causing glaucoma. Anyone with a family history of glaucoma should have their eyes monitored more closely. People over age forty with a family history should have their eyes checked annually. If you are being treated for glaucoma, make sure you are using your medications properly. If you have had laser treatment and do not need medications, you still need to be followed closely.
Find out what your target pressure is and make sure you don’t miss you eye appointments. Almost all patients with glaucoma can maintain their vision if they keep their intraocular pressures at their target pressure and monitor their glaucoma properly.