Postop keratometry not associated with night-vision problems
Effect was predictor of satisfaction, change in halo; but not glare, starburst, ghosting/double vision
San Francisco—Postoperative keratometry does not appear to affect patients’ night vision or satisfaction with LASIK, according to Steven Schallhorn, MD.
“There are many surgeons who won’t do LASIK if the cornea is made too flat by a myopic procedure,” said Dr. Schallhorn, a clinical professor of ophthalmology at the University of California, San Francisco. “But it has a very small and clinically irrelevant influence.”
Few studies have investigated the influence of a flat postoperative cornea on visual degradation, and these have reached contradictory results.
At the same time, a flatter postoperative keratometry is associated with higher attempted myopic correction, which might confound results.
To investigate the effect of keratometry on patient’s night vision and satisfaction, Dr. Schallhorn and his colleagues evaluated 8,672 myopic eyes of 4,602 patients from the database of Optical Express in Glasgow, United Kingdom.
Before surgery, the mean manifest spherical equivalent was -3.72 D, and the mean keratometry (K) value was 43.64.
The researchers compared these statistics to similar measures 1 month after surgery.
“We wanted to look at the early postoperative time period specifically because symptoms are generally worse in the 1-month time period,” Dr. Schallhorn said.
At 1 month after surgery, 93.7% of eyes were within 0.50 D and 99.1% were within 1 D of emmetropia. Similarly 94.6% of eyes achieved monocular uncorrected-distance visual acuity (UDVA) of 20/20 or better, and 98.3% achieved binocular uncorrected distance visual acuity of 20/20.
At the same time, 48.7% of the eyes had a flat corneal meridian (Kmin) of 40.0 D or less, and 6.0% had a Kmin of 37 D or less.
Overall, 95.6% of the patients said they were satisfied or very satisfied with the procedure, while 2.6% were neither satisfied nor dissatisfied and 1.8% were dissatisfied.
The mean scores for postoperative night-vision phenomena were 1.96 for glare, 1.89 for halo, 1.94 for starburst, and 1.39 for ghosting and double vision.
Postoperative keratometry was a small-but-statistically-significant predictor of patient-reported satisfaction, and the change in halo reports. But it accounted for only 0.3% of the variance in patient satisfaction and 0.1% of the variance in halo complaints.
In addition, it was not a significant predictor of changes in reports of glare, starburst, ghosting, or double vision.