Steven C. Schallhorn, M.D., director of cornea services, Naval Medical Center, San Diego, came to this conclusion after an analysis of 105 conventional LASIK patients (210 eyes) involving a 55 mph night-driving simulator.

Patients' best-corrected visual acuity was tested in trial frames before and six months after LASIK. The results were presented at the most recent ASCRS?ASOA Symposium & Congress, San Diego.

This occurred despite more than 70% of patients achieving 20/20 uncorrected visual acuity, he said.

In fact, the patients, on average, experienced a decrease both in target detection and target-identification distance with and without a glare source, Dr. Schallhorn said.

For instance, conventional LASIK patients, on average, had to be 32 feet closer to a business sign in order to detect it, compared to pre-operatively, he said.

The LASIK patients also had to be 36 feet closer compared to pre-operatively in order to identify it, he said. And with a glare source added, the patients had to be

35 feet closer to detect it and 41 feet closer to identify it, he said.

When it came to pedestrians - certainly the more serious target to identify - Dr. Schallhorn said LASIK patients were 19 feet closer than before surgery when detection was made without glare.

With a glare source, the LASIK patients had to be 33 feet closer to make the detection and 35 feet closer to identify the target, Dr. Schallhorn said. These results were statistically significant.

"Poor night vision and difficulty with night driving are risks of the surgery," Dr. Schallhorn said. "That needs to be clear with prospective patients."

A vehicle that moves 55 mph covers 81 feet in one second, Dr. Schallhorn said.

"A one-second reduction in detection is considered significant by the National Highway Traffic Safety Administration," Dr. Schallhorn said.

Determining the problem

While Dr. Schallhorn said the night driving simulator determined that patients frequently had worse night driving ability after conventional LASIK, he also wanted to find out why.

	Thirty-one percent had a measurable increase in night halos complaints after LASIK compared to pre-operatively. Meanwhile, only 5% of patients had a measurable decrease in complaints of night halos after LASIK than before.

"You can see that many more patients had halo complaints after surgery," Dr. Schallhorn said. "Patients that had complaints of halos tended to have worse night driving scores."

Meanwhile, while on average, BCVA improved after surgery, contrast sensitivity worsened, Dr. Schallhorn said.

Twenty-five percent of participants had a loss of two or more lines of contrast acuity after conventional LASIK as measured in a 5% contrast acuity chart.

But Dr. Schallhorn found no correlation between target detection/identification and pupil size.

"With a wide distribution of pupil sizes, we found no significance in pupil size," Dr. Schallhorn said. "However, the level of pre-operative myopia was significant in every category. On average, the higher the myopia, the worse the night driving performance."

There are some limitations to the study, Dr. Schallhorn said. The fact that the study was conducted via monocular testing in trial frames is somewhat of a limitation, he said.

But this study provides "another reason for alternatives to conventional LASIK, such as wavefront-guided surgery," said Dr. Schallhorn, who reiterated that LASIK to correct high myopia puts patients at a higher risk for night vision problems.

Editors' note: Dr. Schallhorn has no financial interests related to his comments.