Glaucoma and Pachymetry

(Corneal Thickness)

Glaucoma is a condition where the pressure inside the eye is too high and there is damage to the structures inside the eye which can lead to decreased vision. The treatment of glaucoma includes decreasing the pressure so damage is prevented altogether or at least its progression is stopped. The examination for glaucoma includes measurement of vision, side vision [visual field], pressure inside the eye, the “drainage” area [“angle”] inside of the eye and very careful evaluation of the optic nerve. Even with all these techniques and measurements, sometimes the question still is not fully answered whether glaucoma exists or not, and, if it does, is it being treated the best way possible.

Ultrasonic pachymetry is a method to measure the thickness of the cornea to within a few microns. The normal cornea is about 550 microns thick. One thousand [1000] microns make one millimeter.

Recently published national studies involving hundreds of people have linked the thickness of the cornea to glaucoma. These studies have shown that if the cornea is too thin, the pressure reading that is taken will be falsely low. The real pressure inside the eye would be higher. The cornea, being thin and “floppy” does not have enough “strength” or “stiffness” against the probe and it indents the eye too much. This gives a falsely low reading with the “real” pressure being much higher. This underestimation of the pressure may give a false feeling that all’s well when in fact it may not be.

For example, if someone has the common type of glaucoma, is being treated with drops and has a pressure of 18 [ the normal pressure is about 10-21] the conclusion would be that this person is being treated well and there is “good” pressure control. If however the corneal thickness is too low, the actual pressure may be above the upper limit of normal and more aggressive treatment may be necessary.

On the other hand, if someone has high pressures and the corneal measurement is thicker than normal, this pressure may be a falsely high. The thicker cornea may be too “stiff” to allow the probe to measure the eye accurately enough and the pressure would be overestimated. This type of person can be more safely examined periodically to look for other signs of glaucoma to guide treatment if necessary.

Corneal pachymetry is now considered the “standard of care” for everyone with glaucoma or who is at risk of developing glaucoma. Pachymetry shows the thickness of the cornea and is a very quick and painless test. It involves using an anesthetic drop on the eye and then gently touching it with a probe. The results take only a few seconds to appear. It need be done only once as the results are stable throughout life.

Currently, there is no reimbursement from Medicare or any other insurance companies for this test. In the not too distant future, there will probably be an approval code to reimburse for this test.

Please feel free to discuss the importance of this test or any reimbursement issues with this office.