Simulator compares night-driving performance with clinical tests

July 15, 2007

The FDA has completed testing in a driving simulator comparing night driving performance to clinical vision tests as a means of assessing the safety of multifocal IOLs. Investigators have not yet determined whether clinical tests such as contrast sensitivity are acceptable substitutes for driving performance in clinical trials of multifocal IOLs.

Key Points

Fort Lauderdale, FL-Preliminary findings from a driving simulation study conducted by the FDA held some surprises.

Investigators have not yet been able to identify clinical tests that would be acceptable substitutes for functional visual performance tests in FDA-required clinical trials of multifocal IOLs, said Bruce A. Drum, PhD, of FDA's Division of Ophthalmic and Ear, Nose, and Throat Devices, Rockville, MD.

The FDA has assessed the comparability of clinical tests with night driving performance in the University of Iowa's National Advanced Driving Simulator in connection with the agency's recommendation that manufacturers of multifocal IOLs evaluate night-driving visual performance. By design, multifocal IOLs have multiple focal points that enable them to offer useful vision over an increased range of distances, but this necessarily reduces the quality of best-corrected vision, said Dr. Drum in a presentation at the annual meeting of the Association for Research in Vision and Ophthalmology.

To investigate possible surrogate measures, the FDA sponsored a clinical trial comparing night driving performance with clinical vision tests. The FDA is examining the results of this trial, which Dr. Drum summarized.

Subjects in the trial completed clinical tests of uncorrected visual acuity (UCVA), contrast sensitivity, and intraocular stray light. In the simulator, they encountered a test route simulating a rural road under various visibility conditions, such as no glare, simulated headlight glare, no fog, and two fog levels with either mild (fog 1) or moderate (fog 2) light diffusion. The fog levels were produced by head-mounted diffusing goggles chosen to simulate multifocal IOL light-scattering properties.

"Fog and glare reduce sign recognition distances separately, but fog plus glare paradoxically improve performance relative to either factor alone," Dr. Drum said. "Fog and glare reduce object recognition distances both separately and in combination. Fog and glare reduce contrast sensitivity to low-frequency gratings both separately and together, similar to object recognition. Fog alone reduces high-frequency contrast sensitivity, but glare, either alone or added to fog, has little effect.

"We are still in the early stages of examining the results of our driving simulation study," Dr. Drum continued. "Although there appear to be some parallels between high-frequency contrast sensitivity and sign recognition, and between low-frequency contrast sensitivity and object recognition, it is too soon to say whether contrast sensitivity can serve as an acceptable surrogate for driving performance in clinical trials of multifocal IOLs."

The trial enrolled 55 patients aged from 30 to 57 years. They were required to have normal vision with UCVA ≥ 20/40. Subjects with systemic disorders or medications that might affect driving performance were excluded. In addition, subjects had to have an unrestricted U.S. driver's license for at least 3 years and have a history of driving at least 3,000 miles per year.

The simulator is owned by the National Highway Traffic Safety Administration and housed at the University of Iowa. Designed to provide the most realistic virtual driving experience available, the simulator is 24 feet in diameter and houses an actual car or truck cab. It can move anywhere within a 64' × 64' area on x and y tracks and can rotate up to 330° and pitch and yaw up to 25°. It contains a 360° by 40° interactive video screen with 20/50 forward resolution, which was modified to 20/20 for this study. Users of the simulator see a dynamic, interactive road scene and generate real-time simulated changes in speed, vibration, sound, car tilt, and road scene with the steering and foot pedal controls.

During the simulation, the subjects encountered three types of traffic signs in random order on the right edge of the road, including street signs, regulatory (speed limit) signs, and warning signs (e.g., bump or soft shoulder). Three road hazards-a ball, a traffic cone, and a suitcase-were presented in random order in the middle of the roadway.