Glaucoma

What is glaucoma? Glaucoma is a leading cause of visual loss that occurs from damage to a type of nerve cell within the retina called the ganglion cell. This damage is visible on an eye exam as damage to the main nerve in the eye, the optic nerve. As glaucoma progresses, this nerve slowly dies and shrinks. This loss of nerve tissue is caused ‘cupping’ of the nerve. Every person has some cupping, but in glaucoma it slowly worsens with time.

Healthy Optic Nerve

Cupped Optic Nerve

It is not known why some people develop glaucoma. However known risk factors include: advancing age, African American race, family history, and elevated eye pressure. Another risk factor is below average thickness of the cornea, which is the clear front part of the eye. The only known method to treat glaucoma is to lower the eye pressure.

Most glaucoma patients have no symptoms until very late in the disease. It usually causes a slow, gradual loss of peripheral vision. It does not affect central vision until very late in the disease. This means it does not blur vision or cause problems reading until very advanced damage occurs. Thus many patients will not realize they have glaucoma for many years. In very advanced disease, patients are left with very small areas of vision, or ‘tunnel vision.’ It is important to diagnose and treat glaucoma as early as possible, because once damage has occurred, it is irreversible.

How does eye pressure affect glaucoma? Glaucoma patients usually have eye pressures that are higher than normal, or above 21. It is felt that this pressure damages the ganglion cells and causes the loss of peripheral vision. However a significant number of patients have eye pressures that are in the normal range, but still develop glaucoma damage. This is called normal pressure glaucoma.

What is the difference between open and closed angle glaucoma? There are two main categories of glaucoma, open angle and closed angle. The “angle” is the part of the eye where the fluid within the eye drains. Many types of glaucoma occur from abnormalities of the angle, which keeps the fluid from exiting the eye. This then causes the pressure to rise, and damages the ganglion cells. With closed angle glaucoma, something is physically blocking the angle. This often occurs in people where the front part of the eye near the angle is crowded. This can cause the iris, or colored part of the eye, to block the angle. Risk factors for this include: being far sighted, Asian race, and advancing cataract. Sometimes this blockage can occur suddenly, causing the pressure to rise very quickly. This is called acute angle closure, and is an emergency which could cause blindness in a matter of hours. Symptoms of this include pain, headache, redness of the eye, blurry vision, and halos around lights.

Open angle glaucoma is more common, and occurs when the angle is not physically blocked. There may still be an abnormality of the angle keeping fluid from properly leaving the eye, but it is on a microscopic scale. Sometimes this is from problems that can be seen on an eye exam, such as excess pigment floating in the eye, inflammation in the eye, or collection of a substance called pseudoexfoliation. More often the angle appears normal on exam, but does not allow fluid to exit properly.

How is glaucoma treated? All types of glaucoma, whether open or closed angle, high or normal pressure, is treated by lowering the eye pressure. Typically this involves one or more eye drops, and sometimes pills. These medications either slow down the fluid production in the eye, or help the fluid to leave the eye.

Additionally, there are multiple in office laser treatments available. Patients with closed angle glaucoma or who are at risk for acute angle closure attacks are treated with a laser that creates a tiny hole in the iris. This allows for a new passageway for fluid to get to the angle and leave the eye. Patients with open angle glaucoma can have a procedure called laser trabeculoplasty. This laser is done in the office and has a high success rate in lowering eye pressure. This can be an effective alternative to daily eye drops.

Sometimes with advanced or difficult to treat glaucoma, surgery in the operating room is necessary. This involves creating a new passageway for fluid to leave the eye, thereby lowering eye pressure. Surgery is typically reserved for patients who have failed other treatments.

OCT of optic nerves showing glaucoma damage

Visual field showing loss of vision.

How will my doctor follow the status of glaucoma? Since the damage from glaucoma is permanent, it is important to diagnose glaucoma early, and to have regular eye exams. Typically a patient will be seen several times during the year to ensure that the eye pressure is at an appropriate level. Since controlling eye pressure is the only treatment for glaucoma, it is important to make sure the pressure is in a safe range. It is very important to take any prescribed glaucoma medications consistently. Missing doses will make the pressure rise, and this can cause the glaucoma to worsen. The doctor will also periodically inspect the optic nerve in the back part of the eye. Changes in the shape of the nerve can signal disease progression. In addition, other tests are done regularly. A visual field test measures peripheral vision loss, and repeated tests allow for detection of disease worsening. Advanced cameras such as OCT measure the shape of the optic nerve in fine detail. They can detect subtle changes that can indicate glaucoma damage.

Glaucoma is a serious disease that usually requires a lifetime of care. However current treatments are very effective in preserving good vision. Early diagnosis, regular follow up with your eye doctor, and consistent use of any prescribed medications are the keys to keeping glaucoma under good control.