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ASCRS SYMPOSIA ASCRS ASOA ANNUAL MEETING by Rich Daly EyeWorld Contributing Writer nioscopy in his lifetime' that I am perfectly satisfied with that," Dr. Radcliffe said. "I really do per- form it any time I want to look." The cost of gonioscopy is "trivial" but the value it provides to patient care is tremendous, he said. Additionally, the results of gonioscopy will vary by 20 to 40 microns, according to research, which makes it reasonable to perform every few years "if things aren't adding up." On examining IOP, Gold- mann tonometry remains the gold standard but "in some patients it's simply impractical to use," Dr. Radcliffe said. In such cases, he uses a Tono-Pen (Reichert), which uses contact applanation. A newer tonometer option is the correcting applanation tonom- etry surface (CATS), which the FDA approved in 2018. That sys- tem redesigned the tonometer tip head to allow more accurate IOP measurement with less influence from corneal thickness, hysteresis, tear film, and corneal curvature. Editors' note: Dr. Radcliffe has finan- cial interests with various ophthalmic companies. The importance of hysteresis can also help clinicians understand why IOP is reduced or not when glaucoma patients are treated with pressure-reduction drops. Research has shown that patients treated with drops for high IOP had very little pressure reduction when they had high hysteresis. "The same relationship is true for corneal thickness, but it is just not as strong of a relationship," Dr. Radcliffe said Additionally, CH predicts the efficacy of selective laser trabecu- loplasty (SLT), according to a 2013 study in Clinical & Experimental Ophthalmology. Specifically, it found baseline IOP and CH accounted for 64% of the variance of the IOP reduction by SLT. These are among the reasons Dr. Radcliffe thinks the use of CH will overtake exams of CCT related to glaucoma. Dr. Radcliffe noted that go- nioscopy is not performed as fre- quently as it should be, according to clinician surveys. Gonioscopy is "priceless" and should be per- formed at baseline on all patients and periodically afterward. "I've already decided that if my tombstone said, 'Dr. Radcliffe performed way too much go- thickness but isn't the same thing," Dr. Radcliffe said. Both CH and CCT differ by race and are lower in older individ- uals. However, CH tends to vary more than CCT between fellow eyes and is on average lower in the eye with the worse glaucoma. Also, unlike CCT, CH is dynamic and increases significantly with decreases in IOP. "So [CH] is a dynamic mea- sure of the cornea's biomechanical abilities," Dr. Radcliffe said. Dr. Radcliffe highlighted a 2018 prospective longitudinal study in the American Journal of Ophthalmology that concluded CH was independently predictive of conversion to glaucoma, even when adjusted for age, IOP, and CCT. It also found that eyes with a lower CH were more likely to develop glaucoma over time. A 2013 study in the journal Ophthalmology found a 1 mm Hg lower CH was associated with a 0.25% per year faster rate of visual field loss over time. It also found that CH explains the impact of IOP on rates of progression. "A high hysteresis is as close to a get out of jail free card for glaucoma that you will find," Dr. Radcliffe said. C entral corneal thickness (CCT) is a stronger risk factor than IOP for the development and pro- gression of glaucoma. While CCT does allow for the correction of IOP measurements, the main value of CCT is its relationship to glaucoma risk, Nathan Rad- cliffe, MD, New York, said at the Glaucoma Essentials symposium sponsored by the ASCRS Glauco- ma Clinical Committee. An illustration of the impact of CCT was that a patient with 30 mm Hg IOP and 600-micron CCT had a 9% risk of developing glaucoma, but a patient with a 20 mm Hg IOP and 500-micron CCT has double the risk of devel- oping glaucoma. "I think that's surprising," Dr. Radcliffe said. He also described CCT as "the current standard for IOP interpretation and glaucoma devel- opment and progression risk." Measuring corneal thickness should include corneal hysteresis (CH), which measures the biome- chanical properties of the cornea. "Corneal hysteresis is very much related to corneal Thickness a better glaucoma predictor than IOP 38 | EYEWORLD DAILY NEWS | MAY 7, 2019

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