Corneal hysteresis measurements in glaucoma patients unaffected by cataract surgery
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Corneal hysteresis measurements remained stable in patients with glaucoma during routine follow-up and after cataract surgery over a 6-month period, according to an analysis published in the Journal of Glaucoma.
“The importance of [corneal hysteresis] in glaucoma is both as a mechanical property of the cornea that can affect the accuracy of IOP measurement and also as a risk factor for the development and progression of glaucoma,” Tzukit Zehavi-Dorin, MD, of the department of ophthalmology at the University of California at San Francisco, and colleagues wrote.
In a retrospective analysis, researchers sought to evaluate the repeatability of corneal hysteresis (CH) measurements in glaucoma patients over a 6-month period at routine follow-up and after cataract surgery. They analyzed 164 eyes of 87 patients who had a minimum of two CH measurements using the Ocular Response Analyzer (Reichert Instruments).
Of 28 patients who had pre- and post-surgical CH measurements (mean follow-up 29.64 ± 9.63 weeks), the mean difference was –0.23 mm Hg, and the measurements were in good agreement (intraclass correlation coefficient [ICC] = 0.79).
Repeated CH measurements for the remaining 136 eyes that did not undergo surgery were in moderate agreement (ICC = 0.64), with a mean difference of +0.3 mm Hg. The mean time between measurements in this group was 32.06 ± 25.32 weeks.
Researchers reported a negative association between the difference in CH measurements and IOP (P < 0.001), writing, “Our data indicates that high IOP is associated with low hysteresis. and when IOP is reduced medically, the hysteresis increases.”
They concluded that CH is affected by high IOPs and does not significantly change an average of 6 or more months after cataract surgery.
“CH appears to be relatively stable in glaucoma patients over the intermediate term,” Zehavi-Dorin and colleagues wrote. “Therefore, the observed reduction in IOP seen after cataract surgery is unlikely to be explained by a change in corneal biomechanics.”
Perspective
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CH, the viscoelastic dampening of the cornea, is a biomechanical property that can affect IOP measurements and a risk factor for the development of glaucoma. With lower CH being associated with more rapid progression of visual field loss, it has been shown to be negatively influenced with increased age and elevated IOPs, but the opposite is true with the use of topical prostaglandin analogs and glaucoma surgery. As such, an association has not been linked to corneal curvature, astigmatism, diurnal IOP variation or soft contact lens-induced transient corneal edema. Interesting, right?
A decrease in IOP is often noted after cataract surgery, but is this association related at all to a change in CH? Zehavi-Dorin and colleagues compared preoperative and postoperative CH measurements with this retrospective analysis. They found that CH is unlikely to explain a change in IOP after cataract surgery, as CH remains consistent in the first 6 months after surgery.
While these findings won’t impact many of us clinically, it is information that will hopefully help guide continued research in this area of interest. As we continue to learn about CH and glaucoma, it's just another reminder that we really don’t know what we don’t know.
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Zehavi-Dorin T, et al. J Glaucoma. 2022;doi:10.1097/IJG.0000000000002008.
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