Cataracts Affect Nighttime Driving Ability

Cataracts and blurred vision result in nighttime driving challenge

(RxWiki News) Passing a state driving test may not necessarily mean driving at night is safe. Those who suffer from cataracts or blurred vision appear to have difficulty recognizing pedestrians at night -- even after passing an eye exam.

Researchers found that even moderate vision impairment in individuals who had passed a driver's license vision test significantly affected their ability to spot pedestrians.

"Skip nighttime driving if you're affected by blurred vision."

Joanne Wood, PhD, a professor from the School of Optometry and Vision Science, and Institute of Health and Biomedical Innovation at Queensland University of Technology in Australia, noted that optical blur and cataracts are very common, but individuals with these medical conditions continue to drive.

During the study, 28 young adults licensed to drive in Australia were asked to drive at night on a closed road wearing simulated reflective blur and cataract lenses. All of the participants had passed the Australia license criteria of 20/40 or better vision.

Pedestrians were present on the course, and they wore one of three types of clothing: all black, all black with a reflective vest; or all black with reflectors on their wrists, elbows, ankles, knees, shoulders and waist to create a sense of human motion. In addition, 16 of the participants were asked to identify pedestrians against a simulated headlight glare.

Investigators found that cataracts caused much more of a visual difficulty than blurred vision. Those with simulated cataracts only recognized pedestrians 30 percent of the time as compared to 52 percent of the time among those wearing goggles that mimicked blurred vision.

Regardless of whether or not there was glare, none of the drivers could recognize pedestrians wearing only black. In comparison, 82 percent could recognize pedestrians wearing reflectors to simulate motion, while only 14 percent spotted bystanders in all black with reflective vests.

They also discovered that drivers with normal vision could identify pedestrians at longer distances. It took those with simulated cataracts 5.5 times longer to recognize pedestrians, and those with blurred visions goggles about 3.6 times longer.

"Future studies should further explore the impact of uncorrected refractive error, cataracts and other forms of visual impairment on driving performance and safety as well as determine the value of some relatively new ways to measure visual abilities, such as straylight testing and contrast sensitivity," said Wood. "It is possible that measuring only visual acuity does not provide us with the best way to determine who is safe to drive."

Dr. Chris Quinn, an optometrist with Omni Eye Associates, said the study confirmed what doctors have known for a while: that what patients can see on an eye chart is not always the best indicator of visual performance.

"Difficulty with night driving is one of most common visual symptoms patients with cataracts complain about even when visual acuity is not severely diminished," he said. "Some patients are aware of the difficulty they have with night driving while some patients don't recognize the limitations imposed on their ability to safely drive at night, especially when they are told their acuity is normal or near normal."

The study was recently published in journal Investigative Ophthalmology & Visual Science.

Review Date: 
April 14, 2012