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Study: Variable, less than optimal levels of UVA protection offered by side windows of cars
Higher UVA exposure on one side of the face might increase the risk of skin cancer and cataract.
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Low levels of ultraviolet A protection provided by side windows in a high number of cars might expose drivers to the negative effects of cumulative UVA light exposure, increasing the risk of cataract and skin cancer.
“We tested 29 automobiles from 15 manufacturers. While the front windshields provide a high and consistent level of UVA protection, most side windows are poorly equipped to do so,” Brian S. Boxer Wachler, MD, said in an interview with Ocular Surgery News.
Several studies have previously shown that skin cancer is more common on the left side of the face in countries where cars are driven on the right side of the road. Conversely, a study from Australia, where cars are driven on the left, found a higher rate of skin cancer on the right side of the face.
“UVA light is also linked to increased risk of cataract formation. A higher prevalence in left eyes has been reported, and it has been suggested that higher UVA light exposure during driving might play a role,” Boxer Wachler said.
To better evaluate the potential risks for a driver’s left eye and left side of the face, Boxer Wachler conducted a study on a variety of automobiles sold by dealers in Los Angeles. A portable UVA light meter (Omega) was used to assess the amount of UVA radiation.
“With each automobile, we measured the external ambient UVA levels with the meter pointed toward the sun. Then we moved the meter inside the car, on the driver’s side, and again pointed it toward the sun through the side window and immediately after through the front windshield,” he said.
The percentage of UVA blockage was calculated by subtracting the UVA energy measured inside the car from the energy measured outside. This figure was divided by the amount of outside UVA energy and then converted to a percentage. A paired t-test was used to compare the UV blockage of front and side windows.
“We also evaluated if older cars had lower levels of UVA protection due to aging of the protective films,” Boxer Wachler said.
Consistent protection in front, variable at side
A high percentage of UVA blockage, varying from 95% to 98%, was found in the windshields of all cars. This was considerably higher than the average 71% of side window UVA blockage.
“The range here was very variable, even within cars of the same manufacturer. One example was Mercedes, which offered 95% protection in the S550 model and only 44% in the E550 model. The most consistently high side window protection, between 92% and 96%, was found in Lexus automobiles, with the exception of an older model, the RX330 of 2005, that had 76%,” Boxer Wachler said.
Recent BMW models offered fairly low 55% side window protection and had a high percent difference, 42%, between side and front. The same applied to the Porsche Turbo S of 2012, in which front protection was 96% and side protection was 56%.
“Type of glass, glass color and coating are the main factors behind the variable amount of UVA protection, while the year of manufacturing was not consistently significant. Interestingly, some older cars offer a higher protection, while specific manufacturers, such as Mercedes and Lexus, have enhanced side window protection in more recent models,” Boxer Wachler said.
He also noted that tinted windows do not provide higher levels of UVA protection. Films that block UVA light are clear. The tint blocks visible light, but some of the cars with tinted windows had the lowest level of UVA blockage.
Useful conclusions
The study has limitations due to the relatively small sample size, but it allowed some useful conclusions to be drawn. First, windshields are accurately manufactured to protect the eyes and face from UVA light.
“They are constructed with two glass panes having a layer of clear plastic in between, which makes the windshield shatterproof in case of accident and also contains the polymers that filter UVA light,” Boxer Wachler said.
Side windows, on the other hand, are made of a single glass pane that may or may not contain a high level of protective UVA filter components.
“We hope to have raised awareness with this study about the need to enhance UVA protection in side windows. The same recommendations could be extended to the manufacturing of glass for residential buildings, hospitals and schools,” he said. – by Michela Cimberle
Reference:
Boxer Wachler BS. JAMA Ophthalmol. 2016;doi:10.1001/jamaophthalmol.2016.1139.
For more information:
Brian S. Boxer Wachler, MD, can be reached at Boxer Wachler Vision Institute, 465 N. Roxbury Drive, Suite 902, Beverly Hills, CA 90210; email: info@boxerwachler.com.
Disclosure: Boxer Wachler reports no relevant financial disclosures.