Diagnosis of Open Angle Glaucoma

When we evaluate a person for Open Angle Glaucoma we are trying to decide how likely it is that the pressure in their eye will damage their vision. Different eyes can tolerate different levels of pressure. The evaluation then must include a measurement of the pressure, but more importantly, an evaluation of the health of the optic nerve. We also must consider the Risk Factors that a patient has such as race, family history, and other existing health problems.

Pressure has been emphasized in the diagnosis of glaucoma, but we now realize that it is only a part of the story. Pressures vary from hour to hour during the day, so that the pressure we measure in the office is only a momentary indication of what the pressure might be during the rest of the day. Pressure measurements are affected by the thickness of the front surface (cornea) of the eye, so that the pressure that is measured only approximates the actual pressure in the eye. Different people can tolerate different levels of pressure. On the other hand, lowering the pressure in the eye is the only known way or reducing the risk of blindness from glaucoma.

People who are of African descent, people who have family members with glaucoma and people with diabetes are at greater risk for getting glaucoma damage.

Much of the examination for Open Angle Glaucoma is designed to determine whether the optic nerve has been damaged. We examine the optic nerve carefully under high magnification through a dilated pupil for evidence of damage. Glaucoma tends to change the shape of the optic nerve in characteristic ways. We will photograph the optic nerve if we are concerned that glaucoma damage may be occurring. This allows careful comparisons to be made in the future for evidence of damage. Newer techniques such as “Scanning Laser Polarimetry,” “Ocular Coherence Tomography”, and “Scanning Laser Tomography” allow us to generate a three-dimensional map of the nerve tissue and facilitate comparisons for signs of damage in the future.

We also measure the peripheral vision or Visual Field for evidence of damage. While the other tests look at the shape of the nerve tissue, the visual field looks at the function of the nerve. Glaucoma tends to damage the peripheral vision in characteristic ways. If vision has been lost, the pattern of vision lost on the visual field can help to confirm that it is due to glaucoma, and help to indicate how severe the damage has been.

Unfortunately, for many people, all of these tests may be inconclusive. There is just too much overlap between normal eyes, and eyes with early glaucoma. Ultimately, what we worry about is whether people are showing signs of worsening. In many cases we use these tests to establish a baseline. Then we re-examine the person periodically for signs of deterioration. As long as no deterioration is occurring it may be reasonable to go without treatment. However, once definite damage has occurred, it is important to start treatment to prevent further damage.