Aspheric IOL shows night driving, contrast sensitivity benefits

July 15, 2007

When a prospective, randomized, observer- and subject-masked study compared an aspheric IOL and a spherical, single-piece IOL for functional performance after implantation in contralateral eyes, contrast sensitivity testing and night-driving performance results favored the aspheric IOL.

Key Points

"The data from this study demonstrate fairly conclusively that the . . . design of the [aspheric] IOL not only is associated with theoretical benefits but has real-world advantages for providing better functional vision," said Dr. Lehmann, a private practitioner in Nacogdoches, TX.

The study enrolled 75 patients in whom the aspheric IOL was implanted in one eye and the spherical IOL in the fellow eye. A subset of 45 patients underwent contrast sensitivity testing with and without glare using a sine-wave grating chart (Functional Acuity Contrast Test, Vision Sciences Research Corp.) viewed through a view-in tester (Optec 6500, Stereo Optical Inc.). Forty-four of those patients participated in evaluation of night-driving performance using a portable night-driving simulator. All of the testing was performed at a minimum of 3 months after implantation in the second eye.

Results of contrast sensitivity assessments consistently favored the aspheric IOL for all comparisons, said Dr. Lehmann, who is also clinical associate professor of ophthalmology, Baylor College of Medicine, Houston.

"The difference between implants was not statistically significant with glare under mesopic conditions, as might be expected when the pupil is small," he said. "However, contrast sensitivity was significantly superior with the aspheric IOL under mesopic conditions without glare at 3 and 6 cpd."

The night-driving simulations were performed with monocular viewing of rural night-driving scenes with low-beam illumination or city-driving scenes with street lights and low-beam illumination. For each of those situations, both detection and identification testing were performed under normal, fog, and glare conditions. The objects that needed to be detected and identified included pedestrians, road warning signs, and text signs.

The results from the night-driving simulation testing also showed consistently better performance with the aspheric IOL, and the differences between implants achieved statistical significance and clinical relevance in multiple comparisons, Dr. Lehmann reported.

In the detection testing, a statistically significant benefit of the aspheric IOL was seen for affording earlier identification of pedestrians under both glare and fog conditions in the city scene. Compared with the eyes in which the spherical IOL had been implanted, stopping time for pedestrian recognition with glare and fog was improved by 0.54 seconds and 0.69 seconds, respectively.

Statistically significant differences also favored the eyes in which the aspheric IOL had been implanted for detection of a text road sign in glare, where the response time also was improved by about 0.5 seconds. For the rural-driving simulation, the time to identify a warning sign in glare, fog, and under normal driving circumstances was improved significantly with the aspheric IOL; the difference compared with the spherical IOL control approached 1 second for each of these situations.

"According to the National Transportation Safety Board, improving the time to react to targets by 0.5 seconds or more represents a clinically relevant advantage for improving driving safety," Dr. Lehmann concluded.