Night-driving simulator may influence future IOL safety tests

In a night-driving simulation, fog and glare separately reduced sign recognition distances but when combined paradoxically increased performance relative to either factor alone. However, fog and glare reduced object recognition both separately and when paired, said Bruce A. Drum, PhD, Division of Ophthalmic and ENT Devices, FDA, Rockville, MD.

Testing at the University of Iowa's National Advanced Driving Simulator was performed in an effort to find an alternative to clinical testing undertaken to meet an FDA requirement that multifocal IOLs be evaluated for night-driving visual performance.

By design, multifocal IOLs improve the range of useful vision but reduce the quality of best-corrected visual acuity, but it is unclear whether existing clinical tests can adequately predict real-world driving performance by individuals with these lenses, Dr. Drum said.

"We designed the study to look at the effects of intraocular scattered light on visual function," Dr. Drum said. "We set up six visibility conditions, including glare, no glare, and three angles of light scatter."

Two fog levels were produced by using diffusing goggles to simulate the light-scattering properties of multifocal IOLs.

To reduce variability, the nonvisual aspects of the subjects' tasks were simplified by designing a simulation involving a straight, deserted country road. Subjects were tested on identification of road signs and their response to hazards in the middle of the road such as a traffic cone, ball, and suitcase. Each was presented under all six glare and fog conditions.

Investigators were surprised by the paradoxical interaction between the effects of glare and fog on recognition distance, Dr. Drum said. Glare alone reduced recognition distance of all targets, as did fog, but the combination of glare and fog filters improved sign recognition but not object recognition. It also appeared that there were different patterns of interaction between glare and fog for low- and high-frequency tasks.

Findings from this study may be useful in designing effective methods of evaluating the safety of multifocal IOLs, such as using contrast sensitivity and stray light tests, Dr. Drum concluded.

The driving simulator study included 55 individuals, aged 30 to 57 years with uncorrected visual acuity of 20/10 to 20/40.