A complete eye exam is essential for the early detection of glaucoma, a serious eye disease that can cause vision loss. During the exam, your optometrist will use a variety of tests to measure the pressure inside the eye, the shape and color of the optic nerve, and the full field of view. These tests include tonometry, gonioscopy, and pachymetry. Additionally, your doctor may perform a field of vision test to determine if you have experienced any loss of vision due to glaucoma.
Glaucoma is a group of diseases that damage the optic nerve. It is the second leading cause of blindness, affecting more than 2.2 million Americans. The most common type is open-angle glaucoma, which accounts for nearly 90 percent of all cases. In this condition, the angle between the iris and the cornea is wide, allowing fluid to flow through the eye.
However, the drainage channels become microscopically obstructed, causing an increase in eye pressure that damages the optic nerve and causes vision loss. Narrow-angle glaucoma is much rarer. In this disease, the angle between the iris and the cornea is not as wide as it should be. As the pupil dilates, intraocular fluid can become trapped, causing an increase in eye pressure and damage to the optic nerve.
Secondary glaucoma refers to any form of glaucoma in which there is an identifiable cause of increased eye pressure. Congenital glaucoma, also known as pediatric or childhood glaucoma, is diagnosed in the first years of life and is often due to improper development of the eye's drainage system before birth. It is important to understand that early detection and intervention are key to preserving vision and slowing the progression of diseases. For a complete eye exam, your doctor will test you for signs of glaucoma.
If signs of the disease occur, you will be referred for a comprehensive evaluation of glaucoma. During this consultation, an eye doctor will examine the eye's internal pressure, the shape and color of the optic nerve, the full field of view, the angle at which the iris attaches to the cornea, and the thickness of the cornea. The doctor will use a Tonopen or Goldmann flattening to measure the internal pressure of the eye. While most cases of glaucoma are diagnosed with a pressure greater than 20 mm Hg (“mm Hg” refers to millimeters of mercury, a scale used to record eye pressure), eye pressure is unique to each person.
The doctor may perform a test called gonioscopy to measure the angle between the iris and cornea. After giving you some drops to numb your eyes, your doctor will place a hand-held contact lens on your eye. Contact lenses contain a mirror that can help the doctor see if the space is blocked or open and open. The doctor can also perform a test called pachymetry, a simple and painless test to measure the thickness of the cornea.
A field of vision test may also be performed to determine if you have experienced any loss of vision due to glaucoma. During this exam, you will be asked to look straight ahead and then indicate when a moving light is passing through your peripheral vision. This helps map your vision. Try to relax and respond as accurately as possible during this test.
Your doctor may want you to repeat this test during your appointment or at future appointments to see if results are consistent. Once glaucoma is diagnosed, visual field tests are usually performed once or twice a year to monitor changes in vision.