Glaucoma is actually a group of diseases whose common feature is an abnormally high pressure inside the eyeball which damages the optic nerve.
The optic nerve is like a giant “electric cable,” containing more than a million nerve fibers, which carries images from the retina to the brain. Blind spots develop in the visual field as the optic nerve deteriorates. This usually starts with peripheral vision.
Glaucoma is sometimes called the “silent thief” since it slowly steals the sight before it is realized. The most common form of glaucoma develops gradually, giving no warning signs and, if left untreated, leads to blindness of both eyes. Many people are unaware of the condition until their vision is extensively damaged.
To understand why this increased pressure can cause such a devastating condition, we must first understand the function of pressure. Internal pressure in the eye is called intraocular pressure (IOP). It allows the eye to hold its shape and function properly. IOP is like air in a balloon – too much can affect the shape and cause it to pop. In the case of the eye, too much can damage the optic nerve, vital to vision.
There are two fluids inside the eye which help maintain IOP. These fluids are the vitreous, which fills the vitreous cavity at the back of the eye, and the aqueous humor, which fills the anterior chamber at the front of the eye.
The continuous flow of aqueous humour is circulated through the anterior chamber before draining out of the eye. It nourishes the lens and the cornea and removes unwanted debris. A healthy eye produces aqueous humor at the same rate that it drains fluid, thus maintaining normal pressure.
Normal pressure ranges from 10 to 22 millimeters of mercury (mm Hg). Anyone with eye pressure over 23 mm Hg is considered at risk for developing glaucoma and requires careful monitoring. People with an intraocular pressure (IOP) greater than 30 mm Hg are considered at high risk.
Aqueous humor exits the eye through a drainage system located at the angle formed where the iris and the cornea meet. Here it passes through a sieve-like system of spongy tissue called the trabecular meshwork and drains into a channel called Schlemm’s canal. The fluid merges into the body’s bloodstream. When the drainage system does not function properly, the aqueous humor cannot flow at its normal rate, and pressure builds within the eye. For reasons not completely understood, the increased pressure gradually damages the nerve fibers that make up the optic nerve.
To receive a diagnosis of glaucoma, a person must exhibit several factors, including an elevated IOP, areas of vision loss, and damage to the optic nerve. In glaucoma, the optic disk will show visible signs of damage. The optic disk is the area where all the nerve fibers come together at the back of the eye before exiting the eyeball.
An optic disk that has been affected by glaucoma appears indented, or excavated, as if someone scooped out part of the center of the disk, a condition known as “cupping.” The normal contour and colour of the disk may be affected by the loss of nerve fibers.
If there is the presence of an elevated IOP, an excavated optic disk, and loss of vision field, the diagnosis will likely be glaucoma. However, if there is only slightly elevated IOP, an undamaged optic nerve, and no visual field loss, there may not be any treatment, but there will be more frequent examinations required to detect any future changes.
If there are signs of optic nerve damage and visual field loss, even though the IOP is within normal range, the doctor will likely advise treatment to lower eye pressure even further which may help slow the progression towards glaucoma.
Tests have shown that when large doses of vitamin C were prescribed, a reduction in intraocular pressure was noted. It is also suggested that avoiding the use of the herb licorice root, as well as high amounts of niacin, tranquilizers, and antihistimines were shown to be beneficial in the treatment of glaucoma.
Although there are many causes of glaucoma, it is most often related to stress and nutritional deficiencies. With the addition of the anti-stress vitamins (for the adrenal glands to respond), vitamin C (which aids in the reducing of pressure behind the eyes), and Vitamin E (which has been found helpful in removing particles from the lens of the eye and for fighting free radicals), glaucoma has improved. Studies done at Yale University show that Coleus forskohlii — used extensively in Ayurvedic medicine – has been effective in treating glaucoma without any side effects.
Certain people are more at risk for developing glaucoma than others. Although having a higher than normal IOP suggests a greater risk of developing the disease, most people with slightly elevated intraocular pressure do not develop the condition.
In the US, blacks are three to four times more likely to develop glaucoma than whites and are six times more likely to suffer permanent blindness as a result. Asian-Americans, particularly those of Vietnamese descent, are also at higher risk. Japanese-Americans are more prone to develop low-tension glaucoma. If there is a history of glaucoma in parents, there is a twenty per cent chance of children developing the disease at some point in their lives. If a sibling develops the disease, the probability of developing glaucoma just rose to fifty per cent. Diabetics and those with hypertension, or heart disease, are other groups at risk.
Other risk factors include retinal detachment, eye tumors, and such eye inflammations as chronic uveitis and iritis. Nearsighted people have a two to three times greater risk of developing glaucoma.
Prolonged used of corticosteroids greatly increases the risk of secondary glaucoma. Structural abnormalities of the eye can lead to secondary glaucoma. For example, pigmentary glaucoma is a form of secondary glaucoma caused by pigment granules being released from the back of the iris. These granules can block the trabecular meshwork.
There are several types of glaucoma. The differences have to do with what is causing the fluid blockage that builds pressure in the eye.
Primary, or chronic, open-angle glaucoma is the most common form of the disease, particularly in older adult women. Open-angle glaucoma is rare before the age of forty, but the risk nearly doubles every ten years after the age of fifty. By the age of eighty, nearly fourteen percent have developed the condition.
Although the drainage angle formed by the cornea and the iris remains open, the aqueous humor drains too slowly, causing fluid backup and, consequently, a buildup of pressure within the eye. Damage to the optic nerve is so slow and painless that a large portion of the vision can be lost before the person is even aware of a problem.
The primary cause is unknown, but it may be that the aqueous humor drains or is absorbed less efficiently with age, but then, not all older adults develop this form of glaucoma. There is evidence to suggest a genetic link. Those with a family history of the disease have a greater risk of developing it themselves.
Open-angle glaucoma usually affects both eyes although symptoms may begin in just one. Other symptoms include: sensitivity to light and glare, trouble differentiating between varying shades of light and dark, and trouble with night vision.
Angle-closure, or closed-angle, glaucoma is a less common form of the disease. It occurs when the drainage angle formed by the cornea and the iris closes or becomes blocked. The aqueous humor is unable to exit through the trabecular meshwork, resulting in an increase in eye pressure. The condition can be chronic or acute. Most people with this type of glaucoma have a very narrow drainage angle, which may be an abnormality from birth. Angle-closure glaucoma is more common in farsighted people who tend to have smaller eyes that can narrow the angle. Normal aging may also contribute. During the aging process, the lens becomes larger, pushing the iris forward and narrowing the space between the iris and the cornea. If there is a narrow drainage angle and the pupils become widely dilated, the angle may close and cause a sudden increase in eye pressure. This acute attack of angle-closure glaucoma requires immediate treatment. Although it often only affects one eye, the other is at risk as well.
Several factors can cause the pupils to dilate: darkness or dim light, stress or excitement, and certain medications including antihistamines, tricyclic antidepressants, and eyedrops used to dilate the pupils, which may not cause the angle to close until several hours after the drops are put in. Acute angle-closure glaucoma is a medical emergency that can cause vision loss within hours of onset. Without treatment the eye can become blind in as little as one or two days. Acute angle-closure glaucoma develops suddenly in response to a rapid rise in eye pressure. An attack often happens in the evening when the light is dim and the pupils are dilated. The symptoms may be severe and include such things as blurred vision, halos around lights, reddening of the eye, headache, severe eye pain, nausea and vomiting, and hardness of the affected eye. Medical attention in such cases must be immediate in order to prevent permanent vision loss which can occur within hours of an attack.
Primary and secondary glaucoma can happen with either open-angle or angle-closure glaucoma and can be either a primary or a secondary condition. It is called primary when the cause is unknown. It progresses with few or no symptoms until the condition reaches an advanced stage. As increased eye pressure continues to damage the optic nerve, more and more peripheral vision is lost. Secondary glaucoma occurs when the condition can be traced to a known cause, as an injury or an eye disease. It may also be caused by a variety of medical conditions, medications, or eye abnormalities or deformities. On rare occasions, eye surgery may also cause the condition. Signs and symptoms of secondary glaucoma vary and depend on the cause and whether the drainage angle is open or closed.
Low-tension glaucoma is an unusual and poorly understood form of the disease. In this form, eye pressure remains within a normal range, but the optic nerve is damaged nevertheless. It is not known why this happens; but some experts speculate that people with this condition may have an abnormally fragile optic nerve or a reduced blood supply to it, which may be caused by such conditions as atherosclerosis which closes arteries. Under these circumstances, even normal pressure on the optic nerve is enough to cause damage.
Tests to detect glaucoma include the following:
Tonometry is a simple, painless procedure that measures IOP and is usually the initial screening test for glaucoma. Two common techniques are air-puff tonometry and applanatation tonometry. Air-puff tonometry uses a puff of air to measure the amount of force needed to indent the cornea. An applanation tonometer is a sophisticated device often fitted to a slit lamp. It is an extremely accurate test that requires the doctor to numb the eyes with drops while the patient is sitting at the slit-lamp. A small, flat-tipped cone is then pushed lightly against the eyeball. The force required to flatten (applanate) a small area of the cornea translates into a measurement of the IOP.
Optic nerve damage testingis done through the use of an ophthalmoscope. This enables the doctor to look directly through the pupil to the back of the eye to check the fibers of the optic nerve. The doctor may also use laser light and computers to create a three-dimensional image of the optic nerve. This can reveal slight changes that may indicate the start of the condition.
Visual field test checks how the visual field has been affected by glaucoma. For this, the doctor uses a perimetry test. One method, known as tangent screen perimetry, requires the patient to look at a screen with a target in the center. The doctor manipulates a small object on a wand at different locations in the patient’s visual field and asks him to indicate when he sees the object come into view. By repeating this process several times, the doctor is able to map the patient’s entire visual field.
Conventional treatments for glaucoma include the following:
- eyedrops (beta-blockers, alpha-adrenergic agents, carbonic anhydrase inhibitors, prostaglandin analogues, prostamides, or maybe even miotics or epinephrine compounds; but these are rarely used today)
- oral medications (carbonic anhydrase inhibitors). With the oral medications and the eyedrops, there are side effects; but some can be quite serious so it is best to learn what these are.
- surgery, called a trabeculectomy, is the final course of treatment. Another type of surgery is the drainage implant surgery performed on people with secondary glaucoma or children with glaucoma.
