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Measurement of corneal hysteresis provides useful information to refractive surgeons

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ATHENS — Measurement of corneal hysteresis with the Reichert Ocular Response Analyzer provides useful information on the dynamic biomechanical properties of the cornea before and after refractive surgery, and it may have a role in predicting postoperative keratectasia, according to surgeons speaking here at the ESCRS Winter Meeting.

A study carried out in New York demonstrated that corneal hysteresis (CH) values, as well as corneal resistance factor (CRF) measurements, are significantly reduced in keratoconus eyes and in eyes following refractive surgery as compared with normal, non-operated eyes.

"While both CH and CRF were around 10 mm Hg in normal and unoperated eyes, in keratoconus and post-LASIK eyes, CH was about 8 mm Hg and CRF was about 7 mm Hg. These measurements may be able to identify eyes at risk of developing ectasia," said Mitsugu Shimmyo, MD.

Caitriona Kirwan, MD, who reported on a study carried out in Dublin, Ireland, said that CH decreased by variable amounts after refractive surgery, with similar changes observed in both LASIK and LASEK patients.

"We found that postoperative hysteresis correlated strongly with residual stromal bed thickness," Dr. Kirwan said.

Similar conclusions concerning CH after LASIK or PRK were also reached in a Greek study presented by Gerasimos Kopsinis, MD.

"Corneal hysteresis was significantly lower in eyes after excimer laser surgery, regardless of the type of procedure used," he said. A moderate regain was observed over time, but it did not achieve preoperative values, however.