You might be surprised at how many tests eye doctors use to diagnose glaucoma. A proper diagnosis requires careful evaluation of many aspects of your eye’s health – from eye pressure to cornea thickness to the health of your optic nerve. This article describes how your eye doctor assesses your risk and all the tests needed to properly diagnose glaucoma.
Your eye doctor will begin by assessing your risk level for developing glaucoma. This will help determine the frequency and extent of testing needed. Through a family history and medical questionnaire, the eye doctor is looking for the following risk factors:
Over the age of 60
Ethnic background such as African or black Caribbean descent, Hispanic, or Asian
Family history of glaucoma, such as a sibling or parent with glaucoma
History of eye conditions, injuries or surgeries
Prolonged corticosteroid use (eye drops, pills, inhalers or creams)
Chronic conditions that affect blood flow, such as migraines, diabetes, low blood pressure or hypertension
Current or former smoker
If you’ve already had a comprehensive eye exam, your eye doctor will also consider these risk factors:
Eye pressure higher than normal (above 21 mmHg)
Thin corneas (less than 0.5 millimeters)
Your type of eyesight is also important. People with farsightedness are at a higher risk for narrow-angle glaucoma, a more serious type that can advance quickly. While nearsightedness is associated with open-angle glaucoma, which progresses slowly without any symptoms.
During a comprehensive eye exam, your eye doctor will always check for glaucoma, regardless of the risk level. This provides a baseline for comparison as you age. There are two tests: tonometry and ophthalmoscopy.
Tonometry measures the pressure within your eye. Your eye doctor will give you drops to numb your eyes. Then he/she will use a device called a tonometer, which applies a small amount of pressure to the eye.
Eye pressure is unique to each person, so it’s not always a reliable indicator for glaucoma. It’s simply another piece of information to help your eye doctor assess your eyes. The range for normal pressure is 12-22 mmHg (“mmHg” in millimeters of mercury, a scale for recording eye pressure). Most glaucoma cases are diagnosed with pressure over 20mmHg. However, some people can have glaucoma at pressures between 12 -22mmHg.
This is an examination of your optic nerve. Your eye doctor will examine the shape and color of the optic nerve, comparing it to an average ratio. Based on the results of these tests, your doctor may ask you to have more glaucoma exams.
Often referred to as OCT, Ocular Coherence Tomography provides a measurement of optic nerve thickness. With OCT, your optic nerve fiber layer is compared to a database of age-matched normals. Changes at the level of the optic nerve can be seen earlier with this technology, providing for earlier diagnosis and treatment.
Perimetry is a visual field test. It creates a map of your complete field of vision. During this test, you’ll look straight ahead and then indicate when a moving light passes your peripheral (or side) vision. Try to relax and respond as accurately as possible. To ensure accuracy, your doctor may repeat the test to see if the results are the same the next time. If you’ve been diagnosed with glaucoma, a visual field test is usually recommended at least once per year to assess changes to your vision.
This diagnostic exam helps determine the angle of your iris and cornea. First, you’ll receive eye drops to numb the eye. A hand-held contact lens is gently placed on the eye. A mirror on the contact lens shows the doctor if the angle is closed and blocked or wide and open.
Last, your eye doctor may want to use pachymetry as another way to confirm a diagnosis. Pachymetry measures the thickness of your cornea, the clear window at the front of the eye. A probe called a pachymeter is gently placed on your cornea to measure its thickness. Thicker corneas are protective against higher eye pressure, while thinner corneas increase risk.
Glaucoma diagnosis is not as simple as you might expect. Be sure to have regular eye exams, especially if you have any of the risk factors, to detect glaucoma early.