Despite the common misconception, glaucoma is NOT a single disease. Rather, it’s the result of a variety of conditions that damage the optic nerve leading to peripheral, and if unchecked, central vision loss. A common misconception is that glaucoma is the same as elevated intraocular fluid pressure (IOP). While elevated IOP is considered an important risk factor for the development of glaucoma, having normal IOP does not necessarily prevent one from developing the condition. Conversely, many people live their lives with elevated IOP and never develop glaucoma.
Our eyes continually manufacture a fluid, called aqueous humor, inside the front portion of the eye. It carries oxygen and various nutrients to the eye’s internal tissues. This fluid drains through a structure called the trabecular meshwork to maintain a steady eye pressure. If the meshwork becomes blocked or less functional, pressure within the eye builds and this can ultimately result in optic nerve damage.
While elevated IOP is an important risk factor, there are a variety of other conditions that can increase a person’s risk for developing glaucoma. Blood flow to the optic nerve is critical in maintaining proper health and function. Therefore, conditions that adversely affect the circulation may result in damage to the optic nerve. These include low blood pressure, migraine, poor blood circulation (Raynaud’s syndrome), diabetes, and inflammation of the blood vessels. Conditions that adversely affect the oxygen content in our blood can also affect the optic nerves, such as sleep apnea and chronic obstructive pulmonary disease. Still other conditions can affect the structural support of the tissues around the optic nerve, making the optic nerves more susceptible to damage. These include high myopia (near-sightedness) and genetic influences. Other important risk factors involved in the development of glaucoma include:
- Advancing age (after age 45, particular after age 70)
- Family history of glaucoma particularly in a parent or sibling
- African American or Hispanic ethnicity for open angle glaucoma
- Asian ethnicity for closed angle glaucoma
- History of serious eye injury
- Use of corticosteroid medication
- Thin corneas
Glaucoma is a leading causes of blindness in the United States….estimated to affect approximately 2.5 million Americans, and only half of those diagnosed are under treatment. Even with treatment, 10 percent of patients can end up blind (estimates suggest 120,000 Americans are blind from glaucoma). As with any chronic condition, early diagnosis and appropriate treatment is critical. Typically, those who lose vision are diagnosed relatively late. Glaucoma is a disease of momentum. The later it is diagnosed, the more difficult it is to control and stabilize. Since most forms of glaucoma are completely symptom-free in early and even moderate stages, early intervention and regular comprehensive eye examinations are critical.
What Are the Different Types of Glaucoma?
In general, glaucoma is separated into two broad categories: Open-angle and Closed-angle glaucoma. Each category is further sub-classified into primary and secondary causes. Primary open angle glaucoma is the most common form in the United States, accounting for almost 90 percent of diagnosed cases. The drainage system looks normal on examination, but progressively loses function over time, resulting in elevated IOP. In susceptible patients, optic nerve damage develops over time. There are a variety of secondary open-angle glaucomas, including those caused by pseudoexfoliation, pigment dispersion, trauma and uveitis (ocular inflammation).
Primary angle closure glaucoma is the result of direct blockage of the drain of the eye, occurring when the iris (colored part of the eye) comes into contact with the drain. People at risk typically have small eyes and are hyperopic (farsighted). Angle closure glaucoma can be acute and marked by the onset of severe eye pain, nausea, headache and rapid visual loss. An attack of angle closure glaucoma is a true medical emergency that needs to be treated immediately to prevent permanent visual loss. Chronic angle closure glaucoma is asymptomatic similar to primary open angle glaucoma.
A complete eye exam, sometimes combined with special testing, is the best way of diagnosing glaucoma. A number of critical components need to be conducted:
- Applanation tonometry, to measure intraocular pressure
- Gonioscopy, to exam the drainage angle
- Ophthalmoscopy through a dilated pupil, to examine the optic nerve
If there is suspicion that glaucoma may be present, additional testing may include:
- Visual field testing to test peripheral vision
- Corneal pachymetry to measure corneal thickness
- Photography of the optic nerves
- Computerized imaging of the optic nerves