The glaucomas comprise a family of disorders that result in loss of vision if not treated. In most cases they are caused by a high eye pressure that results in loss of function of the optic nerve that carries vision signals to the brain. Normal pressure in eyes varies between 10 and 21mm Hg. Sometimes glaucoma develops despite normal pressures in the eyes; these occurrences are known as normal pressure glaucoma. Glaucoma can be inherited genetically or acquired during life. Acquired glaucoma can be due to an old or recent injury, use of steroids (prednisone or cortisone and usually eye drop forms), and inflammatory disorders of the eye or from diabetic or vascular conditions. While most glaucomas arise in older patients, they may begin in midlife and can be seen at any age. There is even a type of congenital glaucoma seen in infants. If glaucoma is present in your family you should be screened by a physician as there are no symptoms.
Most glaucoma is chronic and hereditary. It develops slowly over a decade or longer and is silent during the incipient period. It occurs mostly because of a failure of the drain inside the eye to adequately lower eye pressure. The drain is the “trabecular meshwork.” The failure of drain function is progressive. It results in the elevation of the eye pressure. The pressure increases over time until it causes slow damage to the eye nerve, known as the optic nerve. There is usually no pain even with great pressure elevation as it is slow to increase. The damage to the optic nerve is the cause of sight impairment, vision loss, or blindness. Generally, damage to the nerve is gradual and occurs over months and years. Early damage is best revealed by a careful look at the optic nerve.
In order to confirm the diagnosis of glaucoma, the physician need only find “typical” optic nerve cupping. This can be seen in the face of normal eye pressure and visual field. Conversely, if the eye pressure is higher than normal, glaucoma may be diagnosed even before damage is visible as field loss or optic nerve damage. This is trickier and depends on a careful evaluation of the risk factors for glaucoma development in the face of high pressure. These factors have been described in the Ocular Hypertension and Treatment Study, also known as the OHTS study. This landmark study of patients with high eye pressure and no detectable damage that were treated or followed for comparison (with a control group) over a 7-year period discovered a new risk factor for glaucoma development and confirmed several previously known risks.
Treatment of glaucoma is carried out in most cases by applying eye drops that lower eye pressure. Laser or surgery can also be performed. Treatment prevents worsening but does not improve vision or repair existing damage.
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The most common treatment for glaucoma employs eye drops. There are two methods by which drops lower pressure. Some drops decrease the flow of fluid into the eye. These are known as inflow drugs. The most well known of the inflow agents are the beta blockers such as timolol. The more effective and physiologic method to lower eye pressure is to enhance outflow. This means to improve the natural drainage pathways. These drugs mostly belong to a class ofprostaglandin or lipid agents. These are the most effective means to lower eye pressure. They are used once daily and lower pressure the furthest. There are other medicines including one with features of both inflow and outflow drugs. Drops are the most common treatment for glaucoma.
The downside of drop usage is their need for constant placement by the patient. They can be costly as well and have bothersome side effects. This inconvenience often leads to incorrect usage on the part of the patient. This is termed non-compliance. Poor compliance is an important explanation for worsening despite treatment. For this reason, we prefer to maintain patients on once-daily medicines whenever possible. When these regimens fail to control pressure we often recommend Selective Laser Trabeculoplasty.
Selective laser Trabeculoplasty is used to treat the drainage tissue directly that is blocked and causing the elevated eye pressure. The laser has a biologic effect on the natural drainage tissue enhancing outflow and lowering pressure. It is nearly painless and takes only about 5 minutes. It does NOT always work. It is effective in about 75% of cases and can lower pressure dramatically in some eyes. Maximal pressure lowering occurs in about 6 weeks. The successful reduction can last for 5 years or longer in some eyes but in most cases the median success is about 11/2 to2 years. If it does not work no harm is done. The 2 main risks are pressure elevation following the laser for a few hours (due to inflammation) the second is inflammation which is usually mild and uneventful. Sometimes the pressure elevation after laser can be damaging to sight and requires close monitoring. The eye is pretreated with medicine to blunt this effect. Laser has been shown to be a viable first treatment in patients with glaucoma after the Glaucoma Laser Trial completed in 1992. With the advent of the Selective Laser, I now offer laser as a first treatment in lieu of eye drops for certain patients. Arguably, laser is the safest treatment for glaucoma.
In severe, aggressive, or intractable cases, conventional surgery is required to lower eye pressure. These surgeries lower eye pressure by creating a new drainage outlet in the eye. The most commonly performed surgery is called a trabeculectomy. It can lower pressures to below normal levels. It is highly successful but comes with certain specific risks not seen with non-cutting treatments. Other surgical methods use drainage implants to create and maintain a drainage channel. Many newer techniques are being explored today and will be available to lower eye pressure in the future. All of these methods so far require an operating room and a sterile field, and do not use laser.