Your optometrist will look at several factors to diagnose glaucoma.

Pressure:

First, your doctor will look at the pressure in the back of your eye. This is called the IOP or Intra-Ocular Pressure. Generally, pressures below 21 are considered normal. Many patients will have borderline high pressures (about 20 to 23). If you have this pressure, you are often monitored over time to determine if you have natural high pressures (ocular hypertension) or you have glaucoma. Pressures above 26 to 27 units are usually treated with drops.

Measuring pressure is called tonometry. Pictures of two common tonometers are shown on the LIVING WITH GLAUCOMA page.

Optic Nerve Evaluation:

Your optometrist will look at your optic nerve. Within the nerve is a whitish depression called the “optic cup.” In glaucoma, the optic cup will enlarge which corresponds to a loss of nerve cells and visual loss. Below are three optic nerves. Notice the normal small cup on the top, the large white cup in the middle, and a very large cup on the bottom.

Visual Fields:

Visual fields is a test where you stare into a big white bowl. Small lights are projected within this bowl randomly in all directions. Every time you see a light, you will push a button. The computer will than map what you can see and what you cannot see. Glaucoma causes loss in vision and usually has a certain pattern of vision loss. Below is a picture of this bowl and the button.

The printout’s obtained from the fields may or may not show visual damage. Below are two segments of the printout.

Above is a Grey Scale. It is a general map of vision. Notice the dark black area. This is the normal Blind Spot that we all have in our eyes.

The Pattern Deviation map above comes from the same eye as the Grey Scale. Notice the arc of squares coming off the the blind spot area. This is one of the common changes seen in the visual field and represents a loss of vision in this region.

Retinal Layer Thickness:

There are new highly sophisticated instruments that measure the thickness layers of your retina. Specifically, your optometrist will look at the retinal nerve fiber layer (RNFL). There are several instruments on the market that do this. If your RNFL is thin, this is another piece of information indicating glaucoma.

Look at the green – yellow – red, curvy patterns above. Green represents the normal RNFL thickness for the average patient. The pattern shown show the thickness – from left to right – in the: ear side of your retina (temporal) to the top side (superior) to the nose side (nasal) to the bottom of your retina (inferior). When the pattern dips into the yellow zone, your retina is thinner than average. If the black curvey line dips into the red zone, you are much thinner than average.