Normal-tension glaucoma, also know as low-tension glaucoma, is characterized as progressive optic nerve damage and loss of visual field, but with normal intraocular pressure. It is though to be related to poor blood flow to the optic nerve, which leads to the death of the cells which carry impulses from the retina to the brain. These eyes appear to be open to pressure-related damage even in the high normal range, therefore a pressure lower than normal is often needed to prevent visual loss. This form of glaucoma accounts for one-third of open angle glaucoma and is being increasingly recognized. Angle-closure glaucoma affects half a million people in the United States. In this disease the drain is normal, but there is a blockage to the flow of fluid between the iris and the lens. The outcome is the iris is pushed forward by fluid pressure. There have been tendency for this disease to be inherited, and often several family members will get it. It is shown to be most common in Asians who are far-sighted. There are different kinds of angle-closure glaucoma. The most common form of angle-closure glaucoma is relative pupillary block. In relative pupillary block, aqueous pressure behind the iris plane forces the iris forward. The removal of this pressure gradient can be achieved with laser iridotomy. A second, less common form of angle-closure glaucoma is known as plateau iris syndrome. In plateau iris, the iris is forced into the angle by the presence of an unusually placed, anterior ciliary body. Because this form of angle-closure glaucoma is not due to fluid pressure gradient, it responds poorly to laser iridotomy. If undiagnosed, recurrent angle-closure may develop. Other forms of angle-closure glaucoma of interest to researchers include lens-induced angle-closure, iris cysts, iris tumors, ciliary body rotation due to effusion, dark room provocative testing during ultrasound biomicroscopy, malignant glaucoma.
In acute angle-closure glaucoma intraocular pressure increases suddenly. This sudden rise in pressure can occur within a matter of hours and become very painful. If the pressure rises high enough, the pain may become so intense that it can cause nausea and vomiting. The eye becomes red, the cornea swells and clouds, and the person may see haloes around lights and experience blurred vision. An acute attack is an emergency condition. If treatment is delayed, eyesight can be permanently destroyed. Scarring of the trabecular meshwork may occur and result in chronic glaucoma, which is much more difficult to control. Cataracts may also develop. Damage to the optic nerve may occur quickly and cause permanently impaired vision. Many of these sudden attacks occur in darkened rooms, such as movie theaters. Darkened environments cause the pupil to dilate, or increase in size. When this happens, there is maximum contact between the eye's lens and the iris. This further narrows the angle and may trigger an attack, but the pupil also dilates when one is excited or anxious. Therefore, many acute glaucoma attacks occur during periods of stress. A variety of drugs can also cause dilation of the pupil and lead to an attack of glaucoma. These include anti-depressants, cold medications, antihistamines, and some medications to treat nausea. Acute glaucoma attacks are not always full blown. Sometimes a patient may have a series of minor attacks. A slight blurring of may be experienced, but without pain or redness. These attacks may end when the patient enters a well lit room or goes to sleep. An acute attack may be stopped with a combination of drops which constricts the pupil, and drugs that help reduce the eye's fluid production. As soon as the intraocular pressure has dropped to a safe level, the ophthalmologist will perform a laser iridotomy. A laser iridotomy is an outpatient procedure in which a laser beam is used to make a small opening in the iris. This allows the fluid to flow more freely. Drops will be used to numb your eye so there is no pain involved. The entire procedure takes less than thirty minutes. Laser surgery may be performed on the other eye, as well. Since it is common for both eyes to suffer from narrowed angles, operating on the unaffected eye is done as a preventive measure. Routine examinations using a technique called gonioscopy can predict one's chances of having an acute attack. A special lens which contains a mirror is placed lightly on the front of the eye and the width of the angle examined visually. Patients with narrow angles can be warned of early symptoms, so that they can seek immediate treatment. In some cases, laser treatment is recommended as a preventive measure. Not all angle-closure glaucoma sufferers will experience an acute attack. Instead, some may develop what is called chronic angle-closure glaucoma. In this case, the iris gradually closes over the drain, causing no obvious symptoms. When this occurs, scars slowly form between the iris and the drain and the intraocular pressure will not rise until there is a significant amount of scar tissue formed, enough to cover the drainage area. If the patient is treated with medication, such as pilocarpine, an acute attack may be prevented, but the chronic form of the disease may still develop.
Pigmentary glaucoma is a type of inherited open-angle glaucoma which develops more frequently in men than in women. It most often begins in the twenties and thirties, which makes it particularly dangerous to a lifetime of normal vision. Nearsighted patients are more typically afflicted. The anatomy of the eyes of these patients appears to play a key role in the development of this type of glaucoma. Myopic, nearsighted, eyes have a concave-shaped iris which creates a wide angle. This causes the pigment layer of the eye to rub on the lens. This rubbing action causes the iris pigment to shed into the aqueous humor and onto neighboring structures, such as the trabecular meshwork. Pigment may plug the pores of the trabecular meshwork, causing it to clog, and thereby increasing the intraocular pressure. Miotic therapy is the treatment of choice, but these drugs in drop form can cause disabling visual blurring in younger patients. Laser iridotomy is presently being investigated in the treatment of this disorder.
Primary open-angle glaucoma is the most common form of glaucoma usually in people over fifty. The pressure in the eye slowly rises and the cornea adapts without swelling. If the cornea were to swell, which is usually a signal that something is wrong, symptoms would be present. But this is usually not the case, the disease often goes undetected. It is painless and the patient often doesn’t realize that he or she is slowly losing vision until the later stages. By this time their vision is impaired and the damaged irreversible. There is no visible abnormality in the trabecular meshwork. It is believed that something is wrong with the ability of the cells in the trabecular meshwork to carry out their normal function, or there may be fewer cells present, as a natural result of getting older. Some believe it is due to a structural defect of the eye’s drainage system. Others believe that iris caused by an enzymatic problem. These theories, as well as others, are currently being studied and tested at numerous research centers across the country. Once a significant number of nerve cells are destroyed, blind spots begin to form in the field of vision. In later stages, the central vision is affected. Once visual loss occurs it is irreversible. Researchers have located a gene that causes a subset of Primary Open Angle Glaucoma (POAG) called juvenile open angle glaucoma. Juvenile open angle glaucoma is characterized by its early onset. These researchers have identified a mutation in approximately 3% of adult-onset (POAG) glaucoma patients they tested. Identification of the glaucoma gene provides the possibility of developing accurate and inexpensive methods for testing those who may be predisposed to develop glaucoma, and could lead to more effective treatments. We would soon be able to develop guidelines that recommend that people be screened for this particular genetic defect. Those who carry the defect in this gene would be likely to get glaucoma and should be followed carefully by their ophthalmologists. Now we have the ability to diagnose a subset of people with a predisposition to glaucoma before they have standard signs of the disease and most importantly, before they lose sight could be a huge benefit to their long-term treatment. For the patients who have mutations in this gene researchers hope to be able to determine which of their children will develop glaucoma and which of their children are at no higher risk for glaucoma than the general population. This is the first of many discoveries on the genetics of POAG that will revolutionize the way we think about this disease.
Alphagan ®, (produced by Allergan Inc.), is a new medication which has recently received approval from the Food and Drug Administration for the treatment of open-angle glaucoma and ocular hypertension. Alphagan® lowers intraocular pressure by reducing the production of fluid within the eye (aqueous humor) and by increasing outflow through the uveoscleral pathway. Side effects from this medication reported in clinical trials include burning or stinging upon instillation of the eyedrop and dry mouth. Alphagan® seems to be a promising new drug. It does not appear to have some of the bodily side effects of the beta blockers, including their caution for use in people who have asthma. In addition, researchers clinical studies show that there is less chance of patients building up a tolerance or developing an allergy to this drug. Alphagan® seems to be a promising new drug. This drug will initially be used as a additional therapy with beta blockers such as Timoptic® or Betoptic®, the topical carbonic anhydrase inhibitor Trusopt® or miotics such as Pilocar®. It may also be used as primary therapy in some individuals.
The development of Xalatan® stems from years of research on prostaglandins, which are naturally occurring fatty acids within the body. The FDA reported that this drug appears to work significantly better than standard glaucoma medications. Protaglandins are thought to lower intraocular pressures by increasing fluid outflow through the uveoscleral pathway in addition to the usual way that fluid exits the eye, which is through the trabecular meshwork, a filter-like structure within the eye. One potential drawback of this medication is that it has a side effect of sometimes changing iris pigmentation, due to an increased amount of brown pigment in the treated eye. This medication is now available by prescription.
Laser surgery has become increasingly popular as an intermediate step between drugs and traditional surgery. The most common type performed for open-angle glaucoma is called trabeculoplsty. This procedure takes place between te and twenty minutes, is painless, and can be performed at a doctor’s office or in an out patient facility. The hight energy laser beam is focused on the eye’s drain. Many people think the laser might burn a hole through the eye. Instead, it causes some areas of the eye’s drain to shrink resulting in the areas next to it to stretch allowing the fluid to drain more easily. After surgery you may go home and resume normal activity. The doctor should check your IOP one or two hours later. After this procedure nearly eighty percent of all patients respond well enough to delay or avoid surgery. While it may take a few weeks to see the full pressure-lowering effect of this procedure, during which time you may take your medication, many patients are eventually discontinuing some of their medication. This is not true of all cases. Cataracts do not occur after laser surgery and complications are minimal.
According to a recently published seven-year study by the National Eye Institute, laser therapy is a safe and effective alternative to medications as a first-time treatment for people with glaucoma. In the past, medications were almost always used as a first-time treatment. Researchers caution that neither eyedrops nor laser surgery is a "magic bullet" for long-term control of glaucoma. They noted that two years after the start of treatment, 56 percent of "laser first" eyes and 70 percent of "medication first" eyes needed new or extra medications to control pressure within the eye. Researchers also noted that both treatments caused side effects. However, study results suggested that the side effects of laser treatment were for the most part temporary, or made no apparent difference in the long run, while the side effects of eyedrops were troublesome for some people with glaucoma.
The most common of traditional surgery is called trabeculectomy. In this procedure the surgeon removes a small section of the eye’s drain. This allows it to drain more easily reducing the fluid pressure. This is done under local anesthesia either as an out patient or a brief hospital stay. Although safe about 1/3 develop cataracts within fife years. About ten to fifteen percent require additional surgery.