As we close out National Glaucoma Awareness month, it’s important to address diagnosing glaucoma. How do optometrists diagnose glaucoma? What tests are involved? Which information is more useful or important in diagnosing glaucoma? Diagnosing glaucoma is really about identifying pieces of the puzzle and putting them together to give a picture of current disease status as well as risks for further damage from glaucoma. While there are some tests that are given more weight, there is no one single test that, on its own, gives a diagnosis.
Here’s some of the tests that are vital for diagnosing glaucoma:
this test measures intraocular pressure or internal eye pressure in millimeters of mercury. “Normal eye pressure” is a debated topic, as “normal” may be more person-specific based on other factors. That being said, 10-21mmHg has been considered the “normal range” for a while. Having eye pressures higher than this is a significant risk factor for glaucoma. A patient can have elevated pressures and not have glaucoma. That is referred to as Ocular Hypertension. But, a person can also have eye pressures within 10-21 and still have glaucoma damage. That’s what makes the other glaucoma tests so important.
OCT (Optical Coherence Tomography):
this uses safe, non-invasive light to capture finely detailed images of the layers of the retina.
OCT is an in-office scan that takes only a few minutes to perform start to finish, yet its detailed images and measurements have become the gold standard for diagnosing glaucoma. OCT gives our optometrists the ability to detect loss of nerve fibers from glaucoma earlier in the process. It also helps quantify damage and check for progression and effectiveness of glaucoma treatments over time.
this test maps out a person’s peripheral vision. While OCT tests the structural or physical aspects of glaucoma, visual fields test for functional loss. As glaucoma progresses, it decreases peripheral vision. Advanced stages may results in progression of peripheral loss to more central loss of vision. While the visual field is important, it’s not perfect. It’s a very subjective test. It can be affected a patient’s attention levels, alertness, familiarity with the testing, and other factors. Testing takes about 5 minutes per eye and may be repeated to improve reliability.
Dilated Eye Exam:
this is important for giving the optometrist a clear view of the optic nerve. It’s here where the damage from glaucoma may first be detected within the context of a routine, yearly eye exam. If the optometrist sees thinning of nerve tissue or other suspicious abnormalities of the optic nerve, this would trigger the glaucoma battery of tests. Yet, ongoing dilated exams to visualize the optic nerve are important for monitoring for disease progression. Taking pictures of the nerves may also be a way to monitor for changes over time.
Pachymetry and Gonioscopy:
these are two tests that are also very important in diagnosing glaucoma. Pachymetry measures the thickness of the cornea, the curved outer portion of the eye. It’s here where eye pressures are measured. The thickness of the cornea affects the pressure reading taken by the optometrist. Also, having thin corneas is a risk factor in itself for glaucoma. Gonioscopy uses a special lens to rest on the cornea in order to view the “angle.” The angle refers to the anatomical area of the eye where internal eye pressure is drained. If the angle is narrow, damaged, or displaying other abnormal characteristics it could help in the diagnosis and treatment of glaucoma.
Personal and Family History:
no glaucoma evaluation is complete without a thorough look at history. We know that family history is extremely important. A person with a family history of glaucoma is at a much greater risk for developing the disease themselves. But, personal history is also important. Age is the number one risk factor for developing glaucoma. Ethnicity is also important, as there is higher risk in African Americans, Latinos, and Asians. Other personal risk factors include a history of head/eye trauma, sleep apnea, certain medications, low blood pressure, and more.
All of the above are important in diagnosing glaucoma. Glaucoma is the leading cause of preventable yet permanent blindness, making early detection the key for long term quality of life. There’s no one test that can do it alone. It’s the whole picture that must come into focus to make the correct diagnosis and design the most appropriate list of treatment options. Help us increase awareness of glaucoma by sharing this article with those you around you.
Dr. Russ Beach