Management of Glaucoma

Glaucoma is the leading cause of blindness during adulthood in this country. Many new cases are found each year and many people become blind from it annually. One of the ophthalmologist’s most important roles is to screen for, diagnose, and treat glaucoma.

Glaucoma is a condition in which the pressure inside the eye is too high for the eye to tolerate. The pressure thereby causes damage primarily to the optic nerve which leads to loss of vision. Loss of peripheral (or side) vision often occurs earlier and the eventual loss of even central (straight ahead) vision can occur. The intraocular pressure may be elevated without evidence of ocular damage. That condition is called "ocular hypertension" and may or may not progress to become glaucoma.

In the normal eye, there is a fluid called aqueous humor which is produced by the ciliary body, a structure located behind the iris. This fluid is produced at a fairly constant rate and flows through the pupil into the front part of the eye (called the anterior chamber). The aqueous then flows out of the eye near the point where the iris and cornea join. An area called the trabecular meshwork is a sieve-lie drain through which the aqueous humor percolates as it exits the eye. As well as bathing the internal structures of the eye (such as the lens, iris, and inner part of the cornea) this fluid also helps to maintain the pressure within the eye which in effect keeps the eye inflated.

In most people, the flow of the aqueous humor through the eye continues throughout life without causing problem. If there is a blockage of the usual outflow, there can result an elevation of the pressure inside the eye leading to glaucoma. This condition is similar to a blocked drain in a sink or bathtub. Instead of overflowing, however, the fluid inside the eye exerts increasing pressure on the eye’s internal structures. Although the pressure is distributed evenly, it takes its effect at the weakest point of the eye, the optic nerve, which carries the visual message from the eye to the brain.

As the nerve fibers are injured, the first effected are those which serve the peripheral field of vision. Characteristically the damage at this time goes unnoticed by patients as the central, more acute, vision is spared. As the damage progresses, however, there may be eventual loss of central vision which is used for reading, etc.

Glaucoma is generally divided into two large categories depending upon the confirmation of the drainage angle. The diagram shows both and "open angle" and a "closed angle" configuration. 

The open angle type is by far the most common. In this type of glaucoma, there appears to be some improper function at the level of the trabecular meshwork. Characteristically the pressure rises gradually causing slow damage to the optic nerve. For that reason, open angle glaucoma is largely asymptomatic and generally does not cause pain or redness in the eye.

In the closed angle type of glaucoma (see diagram), the iris may fold over the trabecular meshwork and thereby block it mechanically. In this type of glaucoma, the pressure rises rapidly causing severe pain, redness, and blurred vision. Frequently patients will see halos around lights due to the acute changes in the cornea.

It is noteworthy that there are many other less common forms of glaucoma. But whatever the cause, it is the resultant increase in intraocular pressure which ultimately causes the damage.

The diagnosis of glaucoma is made by careful and thorough examination of the structures and function of the eye. Particular attention is paid to the measurement of the patient’s intraocular pressure, the configuration of the optic nerve, and careful evaluation of the peripheral vision (visual field). After analysis of data, if the patient is deemed to have glaucoma, treatment is then directed toward lowering the intraocular pressure to a level which will not allow further damage to the optic nerve. The first line of treatment is usually eyedrops and/or oral medication. If medications do not work, laser surgery or other forms of surgery may be employed. We will limit our discussion in this issue to medical treatment.

Topical Medications (Eyedrops)

There are several types of eyedrops that are available, each of which have both the desired pressure-lowering effect as well as undesired side effects. The job of the physician is to balance the good effects with the occasional side effects in order to achieve the best possible lowering of the intraocular pressure. It is most desirable to lower the pressure to a level which should be safe for the remainder of the patient’s life.

Miotics are the oldest and best known of these pressure-lowering medications. These medications are so named because they constrict the pupil. Their probably mechanism of action is an opening of the trabecular meshwork where the aqueous humor filters out of the eye. These medications are available in various strengths and durations of action. Most last for only a few hours but some have an effect lasting for one or two days. Pilocarpine is the best known and most commonly prescribed drug in this group.

It is unfortunate that the side effects on miotics are a frequent problem. Since these medications constrict the pupil, they limit the amount of light entering the eye, which can cause a dimming of the vision. Additionally, they can cause discomfort (aching) upon instillation as well as blurring the vision by affecting the muscles within the ciliary body which serve to focus the lens. For these reasons, miotics are not often useful in younger people. Retinal detachment has also been reported as a complication of miotic use. Additionally, the development of cataracts and allergic reactions may occur.

There have been some recent developments to improve the method in which these drugs may be delivered. One example is an ocusert, a small, wafer-like insert that delivers very small doses of pilocarpine over a week’s time. This slower delivery lessens the side effects while providing an effective method of delivering the drug. More recently, a pilocarpine gel has been introduced for use at bedtime. This medication is also showing promise, although there have been some undesired effects reported at the level of the corneal surface.

The next class of drugs to be considered are the adrenergic (adrenaline) drugs. These medications are either adrenaline or a compound similar to it which seem to cause their pressure-lowering effect also at the level of the trabecular meshwork. These medications may also reduce the production of aqueous humor at the ciliary body.

One of the more promising developments within this family of drugs was the introduction of Propine which changes to adrenaline inside the eye. There are, therefore, fewer side effects because there is less absorption of adrenaline into the bloodstream which can cause elevation of the blood pressure or increase in the heart rate. Side effects of these medications also include excessive redness, allergic reaction, or increase in the pupil size.

Another advance in topical eye medication was the development of adrenergic blocking drugs. The first one of this class was Timoptic. Other eyedrops in this category include Betopitic, Betagan, OptiPranolol, and Ocupress. These medications probably cause their beneficial effects by reducing the formation of aqueous humor. Unfortunately, serious side effects may occur through the absorption of these medications into the bloodstream. These adrenergic blocking agents can cause a serious slowing of the heart rate with a lowering of the blood pressure and heart failure. Additionally, patients with asthma cannot take this class of eyedrops as they can precipitate severe asthmatic attack.

Systemic or Oral Medications

Diamox, Neptazane and Daranide are the most common medications prescribed within this group. These drugs, which are taken by mouth, block the action of an enzyme called carbonic anhydrase and thereby slow down the production of aqueous humor. There are generally used for the short-term control of intraocular pressure but may be used for longer periods in those who can tolerate their side effects.

Tingling of the extremities (especially fingers and toes), a change in the taste of carbonated beverages, loss of appetite with weight loss, depression, and an overall feeling of fatigue are among the more common side effects of these medicines. Kidney stones, lowered potassium, and allergic reactions (as those of sulfa-based drugs) can also occur.

In summary, the diagnosis and satisfactory treatment of glaucoma demands the utmost skill and care from the eye physician -- the ophthalmologist. Accurate diagnosis, careful follow-up, and regular evaluation are mandatory for the successful, long-term management of glaucoma. We feel that proper glaucoma treatment is one of our most important functions as ophthalmologists. It is necessarily a highly personalized and demanding art and science.

In conclusion, this article is not meant to cover the complex topic of glaucoma in its entirety, but we do hope that it conveys some of the important concepts in the diagnosis and management of this common cause of blindness in persons over 40.