By Nathan Radcliffe, MD
Clinicians often ask me for specific examples of how Corneal Hysteresis impacts my glaucoma decision making. At present, I am managing a diabetic patient with a history of macular edema (and some residual edema) in my practice who was on three drops and still had a pressure of 24. Normally I would rely heavily on visual fields and OCT to decide next treatment options in this situation, but in this case her OCT was simply not very useful in terms of helping me know how much RNFL atrophy there was because of the edema. I think most clinicians can relate, we all have these situations where you are tempted to start treating the pressure because you've lost your radar.
There is another critical risk factor to consider. In my practice every patient gets their Corneal Hysteresis measured by the Ocular Response Analyzer® G3. For this patient, her Corneal Hysteresis was 11.5, which is higher than the average normal value of about 10.5.
It’s important to reflect on the findings of Bob Weinreb, MD, and Felipe Medeiros, MD, in the Diagnostic Innovations in Glaucoma Study.1 They monitored subjects’ visual fields progression over time and divided them into low and high Corneal Hysteresis groups. All of the rapid progressors were in the low Corneal Hysteresis group. There were no rapid progressors in the high Corneal Hysteresis group. Even though these patients had glaucoma, in the high Corneal Hysteresis group, the slopes were flat. They certainly weren't getting worse quickly and they weren't really getting worse at all over three or four years. So high Corneal Hysteresis was shown to be protective against glaucoma progression in this (and other) studies.
For my diabetic patient, the high Corneal Hysteresis value not only helped me decide not to escalate therapy, even though their IOP was 24, but to back off the drops and see if we can keep her on just one of the three. The pressure may still stay at 24, but because of the high Corneal Hysteresis I am willing to just monitor her. We learned from one of my studies that patients who have high Corneal Hysteresis typically don’t get much of a response from IOP lowering therapy – and we need to fully understand why this is – but the data proves it. Knowing this really helps me anticipate who my responders and non-responders are going to be. I am more comfortable tolerating an IOP that is higher than I normally would if the patient has high Corneal Hysteresis. On the contrary, if the patient has low Corneal Hysteresis, I might not tolerate a seemingly well controlled IOP and want to get more aggressive with that patient. Corneal Hysteresis really plays a key role in the way I decide to risk stratify and manage my glaucoma patients.
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1. Felipe A. Medeiros, MD and Robert N. Weinreb, MD. Diagnostic Innovations in Glaucoma Study (DIGS): Diagnosing Glaucoma with Spectral Domain Optical Coherence Tomography in Patients Suspected of Having the Disease. Investigative Ophthalmology & Visual Science March 2012, Vol.53, 5620.