By Jean E. Keamy
Patients often come to my office and wonder if they have glaucoma. Another group of patients think that just because they have normal pressures (tonometry) that they do not have glaucoma. Since glaucoma is one of the leading causes of blindness, I thought a review of what glaucoma is and how it is diagnosed would help my readers.
Glaucoma is a set of eye diseases that refers to damage of the optic nerve as a result of increased aqueous humor in the eye. The aqueous humor drains through the trabecular meshwork in the angle between the iris and cornea. When the eye produces too much aqueous humor or when the outflow is reduced, the intraocular pressure can rise. This increased pressure can lead to damage to the optic nerve.
The optic cup sits within the optic disk. The usual ratio of cup to disk is less than 0.4. When the optic cup becomes larger or the cup to disc ratio increases, the optic nerve can become damaged and result in loss of vision.
There are several types of glaucoma. Open angle glaucoma means that there is no anatomical obstruction to outflow. Despite this, the pressure can increase, leading to damage to the nerve. In a small subset of patients, even normal pressures can result in damage, called low-tension glaucoma. Open angle glaucoma develops slowly over time. The risk increases with age. There is no known cause of open angle glaucoma; however, it is often hereditary.
Closed angle glaucoma results from anatomical obstruction of fluid outflow. Some patients have narrow angles without glaucoma. Usually a prophylactic procedure called a laser iridotomy to open the angle is recommended to prevent the development of glaucoma. Closed angle glaucoma can come on suddenly. It results in acute pain and acute vision loss.
By the age of 40, everyone should have a complete eye exam. Patients with a family history of glaucoma should be screened earlier. Since pressures can be normal in low-tension glaucoma, more than just pressure should be examined. An examination of the angles and the optic nerve are necessary. If there is any suspicion of glaucoma, additional tests are necessary every year. They include imaging of the optic nerve with photographs, nerve fiber layer analysis with a HRT or OCT, and a visual field. The management of glaucoma includes eye medications, laser treatments, and sometimes surgery to help reduce intraocular pressure and preserve vision. Although there is no cure to glaucoma, an early diagnosis can help prevent vision loss.
Dr. Jean Keamy is a board certified ophthalmologist specializing in cataract surgery, glaucoma detection, refractive surgery, eye lid surgery and diseases of the eye. She owns Keamy Eye & Laser Centre on 24 Lyman St. in Westborough and can be reached at 508-836-8733. Learn more at www.seemedrkeamy.com.