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Figure.
Distribution of Percentages of Front-Windshield UV-A Blockage and of Side-Window UV-A Blockage for the Same Vehicles
Distribution of Percentages of Front-Windshield UV-A Blockage and of Side-Window UV-A Blockage for the Same Vehicles

The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98% [95% CI, 95.7%-96.3%]) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96% [95% CI, 66.4%-75.6%]) (P < .001). The percentages of UV-A blockage for each automobile’s front windshield and driver’s side window were calculated by subtracting the UV-A energy measured behind the window from the outside UV-A energy. That figure was divided by the amount of outside UV-A energy. This fraction was converted to a percentage by multiplying by 100.

Table.  
Data on the Automobiles Tested, UV-A Measurements, and Percentages of UV-A Blockage
Data on the Automobiles Tested, UV-A Measurements, and Percentages of UV-A Blockage
1.
Chylack  LT  Jr.  Mechanisms of senile cataract formation.  Ophthalmology. 1984;91(6):596-602.PubMedGoogle ScholarCrossref
2.
Chang  C, Murzaku  EC, Penn  L,  et al.  More skin, more sun, more tan, more melanoma.  Am J Public Health. 2014;104(11):e92-e99.PubMedGoogle ScholarCrossref
3.
Butler  ST, Fosko  SW.  Increased prevalence of left-sided skin cancers.  J Am Acad Dermatol. 2010;63(6):1006-1010.PubMedGoogle ScholarCrossref
4.
Paulson  KG, Iyer  JG, Nghiem  P.  Asymmetric lateral distribution of melanoma and Merkel cell carcinoma in the United States.  J Am Acad Dermatol. 2011;65(1):35-39.PubMedGoogle ScholarCrossref
5.
Hirvelä  H, Luukinen  H, Laatikainen  L.  Prevalence and risk factors of lens opacities in the elderly in Finland: a population-based study.  Ophthalmology. 1995;102(1):108-117.PubMedGoogle ScholarCrossref
6.
Bernstein  EF, Schwartz  M, Viehmeyer  R, Arocena  MS, Sambuco  CP, Ksenzenko  SM.  Measurement of protection afforded by ultraviolet-absorbing window film using an in vitro model of photodamage.  Lasers Surg Med. 2006;38(4):337-342.PubMedGoogle ScholarCrossref
7.
Abraham  AG, Cox  C, West  S.  The differential effect of ultraviolet light exposure on cataract rate across regions of the lens.  Invest Ophthalmol Vis Sci. 2010;51(8):3919-3923.PubMedGoogle ScholarCrossref
8.
Foley  P, Lanzer  D, Marks  R.  Are solar keratoses more common on the driver’s side?  Br Med J (Clin Res Ed). 1986;293(6538):18.PubMedGoogle ScholarCrossref
9.
Castanedo-Cazares  JP, Ehnis-Pérez  A, Zúñiga-Yudiche  M, Torres-Alvarez  B.  Motor vehicles and ultraviolet exposure in Mexico [in Spanish].  Rev Invest Clin. 2012;64(6, pt 2):620-624.PubMedGoogle Scholar
10.
Tuchinda  C, Srivannaboon  S, Lim  HW.  Photoprotection by window glass, automobile glass, and sunglasses.  J Am Acad Dermatol. 2006;54(5):845-854.PubMedGoogle ScholarCrossref
11.
Edlich  RF, Winters  KL, Cox  MJ,  et al.  Use of UV-protective windows and window films to aid in the prevention of skin cancer.  J Long Term Eff Med Implants. 2004;14(5):415-430.PubMedGoogle Scholar
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    1 Comment for this article
    EXPAND ALL
    UV A and B Autoglass Penetration
    Rahmin A. Rabenou, M.D., Austin Cope, MD, MBA | Department of Medicine, Southern Arizona VA Healthcare System
    Comment:

    The author states that the level of UV A auto glass protection for drivers is unknown. At least for Honda (and likely the other major manufacturers) this is not entirely accurate. We have spoken to Honda Customer service. The 2015 Honda Accord side window and windshield both block 46% of UV. This is very different from the values in this paper listing 97% and 98% UV A blockage for 2012 and 2013 models. I doubt the level of protection has dropped 50% in 2 years. This paper lists a much higher
    level of protection which could lead care providers to falsely reassure patients that they are adequately UV A protected in their vehicles.

    The author's assumption that UV A and B penetration levels will be similar is not accurate based on UV wavelength and penetration differences. Glass filters out UV B very effectively, but not UV A. Therefore, most car window UV penetration can be assumed to be much higher for UV A which is a longer wavelength than UV B. In order to better understand this, it is important to understand the differences in side window and windshield manufacturing techniques. Side windows are often made of a single layer of tempered glass while the windshield is made of laminated glass with a polyvinyl middle layer for crash protection. The polyvinyl can absorb UV B decreasing penetration.

    This paper fails to differentiate factory smoked/tinted from dealer tinted windows. Factory darkened windows lack a protective UV film. This is particularly common in back windows where children often sit. Tints added by the dealer or owner, consists of a darkened film applied over the glass. These film overlays often contain ceramic or metallic particles which are responsible for their UV protective properties. The films are also available as non tinted for UV only protection. These should be considered for the back seat to protect children sitting behind a factory smoked/tinted window. If in compliance with state law, they can also be considered for the windshield where tinting needs to be avoided for driving safety.

    When purchasing an automobile, new owners should contact the automobile customer service and ask for the UV specifications. If the car appears tinted, the customer should ask if the tinting is from the original manufacturer, or added later. If original, then consider adding a clear protective UV film. If added later, the dealer will know what type of tint film was used. The amount of UV protection can then be looked up.

     ________________________

    Response from Dr. Boxler Wachler:

    I would like to thank the commenters for the thoughtful letter regarding my study.  

    They write “The author states that the level of UV A auto glass protection for drivers is unknown.  At least for Honda (and likely the other major manufacturers) this is not entirely accurate.”   They also reported a recent phone call with Honda customer service to inquire about the UV protection of a 2015 Honda Accord.   Honda customer service said that car’s side window and windshield block 46% UV.  To validate this information, we also called Honda customer service on two different occasions on June 2, 2016.  During the first call, one representative stated that Honda stopped releasing that information in 2007 and he did not have a reason when asked for one.  During the second call later that day, a different representative instructed us to call the operator and request the marketing department.   We did that and spoke with yet another representative but our call was dropped in the process of transfer.  We called back and still another representative asked if we wanted ‘national marketing’ or ‘regional marketing’.  We said ‘national marketing’ and there was no answer and our call was put back in queue to the operator who sent us to the research and development department who transferred us back to the main Honda switchboard who transferred us to yet another representative who put us on hold for a few minutes came back and told us that Honda abides by all federal and state guidelines and stated that there was no department that would have more detailed information than what he just said.  All together, we were on the phone with Honda for about 30 minutes.  So, our experience of obtaining UV side window and front windshield information from Honda was very different than the commenters.   

    Additionally, federal law requires front windshields of all vehicles to have near complete UV-A blockage so the commenters' report that Honda customer service said the windshield blockage is 46% is potentially problematic on two levels:  1) the customer service representative is not reporting correct information or 2) Honda is in violation of federal law for automobile manufacturing of front windshields.

    The commenters stated that I assumed UV-A and UV-B penetration levels are similar in my paper.   There was not a single mention in the paper of “UV-B”, so I am not clear regarding the basis for the statement.  They also stated that it is important to understand the differences between windshield and side window construction and then proceeded to explain it.  My paper also discussed these manufacturing differences in the third paragraph of the Discussion section.

    The commenters point out that I did not differentiate between factory smoked/tinted windows and dealer tinted windows.   That is correct but I am not sure how it is relevant.  If a driver has a vehicle with a side window tint (regardless of the source of the tint), my study found that one cannot assume the tinted window has full UV-A protection.

    In the last paragraph, the commenters advocate for new owners to call their company's customer service to obtain UV information about the windows.  My response is: I hope they have better luck than us.





     



    CONFLICT OF INTEREST: None provided
    READ MORE
    Original Investigation
    July 2016

    Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows

    Author Affiliations
    • 1Boxer Wachler Vision Institute, Beverly Hills, California
     

    Copyright 2016 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.

    JAMA Ophthalmol. 2016;134(7):772-775. doi:10.1001/jamaophthalmol.2016.1139
    Abstract

    Importance  Ultraviolet A (UV-A) light is associated with the risks of cataract and skin cancer.

    Objective  To assess the level of UV-A light protection in the front windshields and side windows of automobiles.

    Design  In this cross-sectional study, 29 automobiles from 15 automobile manufacturers were analyzed. The outside ambient UV-A radiation, along with UV-A radiation behind the front windshield and behind the driver’s side window of all automobiles, was measured. The years of the automobiles ranged from 1990 to 2014, with an average year of 2010. The automobile dealerships were located in Los Angeles, California.

    Main Outcomes and Measures  Amount of UV-A blockage from windshields and side windows. The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98% [95% CI, 95.7%-96.3%]) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96% [95% CI, 66.4%-75.6%]). The difference between these average percentages is 25% (95% CI, 21%-30% [P < .001]). A high level of side-window UV-A blockage (>90%) was found in 4 of 29 automobiles (13.8%).

    Conclusions and Relevance  The level of front-windshield UV-A protection was consistently high among automobiles. The level of side-window UV-A protection was lower and highly variable. These results may in part explain the reported increased rates of cataract in left eyes and left-sided facial skin cancer. Automakers may wish to consider increasing the degree of UV-A protection in the side windows of automobiles.

    Introduction

    The risks of sun exposure to the skin and eyes are well known. People who drive cars and other motor vehicles expose the left sides of their faces, including their left eyes, to sunlight and solar radiation because that side is near the side windows, which increases the risk of various diseases in the left eye and on the left side of the face. Ultraviolet A (UV-A) is linked to increased risks of cataract formation1 and skin cancer.2 Studies have found that skin cancers are more common on the left side of the face.3,4 It has been reported that left eyes have higher rates of cataract because drivers are seated on the left side of the automobile (and drive on the right side of the road).5 UV-A light that passes through glass without UV-A protection has led to in vitro cytotoxic effects on cells, whereas glass with UV-A protection dramatically reduced the cytotoxic effect of UV-A light.6 Therefore, auto glass with UV-A protection would be expected to reduce the risks of disorders related to sun damage. In the United States, the level of auto glass UV-A protection for drivers of different makes and models of vehicles is unknown.

    Box Section Ref ID

    Key Points

    • Question What is the difference in the level of ultraviolet A (UV-A) light protection between the front windshield and the side windows of an automobile?

    • Findings In this cross-sectional study, the average percentage of front-windshield UV-A blockage was 96%, which was 25% higher than the side-window blockage. A high level of side-window UV-A blockage (>90%) was found in 4 of 29 automobiles (13.8%).

    • Meaning These results may in part explain the reported increased rates of cataract in left eyes and left-sided facial skin cancer.

    Methods

    I undertook this study to evaluate the levels of UV-A penetration of a variety of vehicles’ front windshields and side windows to better understand the levels of UV-A protection and the risks for drivers’ left eyes and the left sides of their faces. This study was undertaken in the late morning and afternoon on May 4, 2014 (a cloudless day), when I visited a number of automobile dealerships in Los Angeles, California, with my daughter Micaela Boxer Wachler, who assisted me in the collection of data and is a student. Dealerships were selected for their proximity because they were all clustered within approximately a half a mile from each other. A variety of makes, models, and years of vehicle production were assessed. A handheld UV-A light meter (Omega) was used to assess the amount UV-A radiation. Test-retest reliability was subsequently evaluated, and no measurement with this device differed by more than ±0.02 mW/cm2. We measured external ambient UV-A levels (with the meter pointed in the direction of the sun for each measurement) for each selected automobile; we did not rely on a single measurement for all automobiles because ambient UV-A changes during the day. Immediately following this measurement for a given selected automobile, the UV-A meter was then held on the inside of the driver’s side window for measurement and oriented in the direction of the sun. The UV-A meter was then held immediately behind the driver’s side of the front windshield for measurement and pointed in the direction of the sun.

    The percentages of UV-A blockage for each automobile’s front windshield and driver’s side window were calculated by subtracting the UV-A energy measured behind the window from the outside UV-A energy. That figure was divided by the amount of outside UV-A energy. This fraction was converted to a percentage by multiplying by 100. A paired t test was used to compare the UV-A blockage of front windshields with that of side windows, and simple linear regression analysis was performed using 2 variables: side-window protection (dependent variable) and vehicle year (StatView; SAS Institute Inc), in order to assess whether older cars had lower levels of UV-A protection as a possible result of aging UV-A window films. Statistical significance was set at P = .05.

    Results

    We analyzed 29 automobiles from 15 automobile manufacturers. The years of the automobiles ranged from 1990 to 2014, with an average year of 2010. The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98% [95% CI, 95.7%-96.3%]) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96% [95% CI, 66.4%-75.6%]). The difference between these average percentages is 25% (95% CI, 21%-30% [P < .001]). A high level of side-window UV-A blockage (>90%) was found in only 4 of 29 automobiles (13.8%). Regression analysis of the association between side-window protection and vehicle year of manufacturer resulted in the correlation coefficient r2 = 0.04 (P = .75).

    The Table provides data on the automobiles tested, along with the UV-A measurements and percentages of UV-A blockage. The Figure shows the distribution of percentages of front-windshield UV-A blockage and the more variable distribution of percentages of side-window UV-A blockage for the same vehicles.

    Discussion

    Cortical cataracts have been reported to occur more in left eyes than right eyes.5 We discovered that, after visual inspection of summary photographs of the crystalline lenses in another study,7 there was increased cortical cataract formation in left eyes than right eyes. These results seem to indicate that left-sided sun exposure for drivers plays a role in the development of cataracts.

    Cumulative UV-A exposure is a significant risk factor for skin cancer. Multiple studies have found that such cancers are more common on the left side of the face in countries where automobiles are driven on the right side of the road.3,4 The faces and arms of these drivers are preferentially exposed to the sunlight. A study from Australia, where automobiles are driven on the opposite (left) side of the road, found that drivers had more skin cancer on the opposite (right) side of the face.8

    The present study found that front windshields, not side windows, offer consistent protection for drivers’ eyes and faces against the harmful effects of UV-A light. The reason lies in the design of the front windshields. These windshields are constructed from 2 planes of glass with a clear layer of plastic “wedged” in between them. This plastic makes the windshield shatterproof in the event of an accident. The plastic layer largely contains the UV-A protection. In contrast, the side windows of cars are a single plane of glass that may or may not have a high level of UV-A–blocking polymers and other protective components. In addition, a number of automobiles had a factory window tint on the side windows, but it did not correlate with increased UV-A blockage.

    To the best of my knowledge, I believe that this is the first US study to analyze and compare the percentages of UV-A blockage between front windshields and side windows. A PubMed search revealed one other study9 that assessed the UV-A radiation passing through automobile windows. This study by Castanedo-Cazares et al9 was from Mexico and had similar findings of consistent and high levels of UV-A blockage from all vehicle front windshields. They found that side windows had statistically lower levels of UV-A protection than front windshields. The average percentage of side-window protection in the Mexico study9 was 84%, which was higher than the average percentage of side-window protection of 71% in the present study. In addition, the Mexico study9 did not find any significant differences in levels of side-window UV-A protection among the vehicles tested, whereas there was a large range of differences in levels of side-window protection in the present study. The reason for this difference between the Mexico study9 and the present study is not well understood. The Mexico study9 did not specify which vehicle makes and models were tested.

    The Table demonstrates that the highest level of UV-A side-window protection was found in newer Lexus models (92%-96%) and a newer Mercedes automobile (95%). Porsche and BMW models had among the lowest levels of side-window protection (56% and 55%, respectively), which were lower than a 1990 Buick (65%). The high level of variability may be explained by the type of glass used by the automaker. The level of UV-A protection varies depending on glass type, glass color, and coating, among other factors.10 There was reasonable consistency regarding side-window UV-A protection among automobiles of a similar year from the same manufacturer (Lexus and Honda). Some cars of different years from the same manufacturer showed higher levels of side-window UV-A protection in more recent year models (Lexus, VW, and Mercedes). I would expect UV-A measurements to be similar across different ambient lighting conditions; however, we did not assess that variable.

    Some patients in my practice have assumed that an automobile with tinted windows will provide a high level of UV-A protection. Tint provides blockage of visible light. Films that purely block UV-A light are virtually clear. Indeed, some tints provide a high level of UV-A protection, whereas others do not. Our observation was that some of the automobiles with tinted windows (eg, BMW) had the lowest levels of UV-A blockage. Therefore, one cannot assume that tinted side windows are providing a high level of protection against UV-A light.

    There are limitations to the present study. For example, we evaluated a specific number of makes and models. There are other types of vehicles that were not part of the present study, and the levels of side-window protection for those automobiles are unknown. It is possible that side windows with a lot of scratches could reduce the efficiency of side-window blockage. We did not observe any side windows with noticeable scratches. Aging of the windows could be a factor in reducing UV-A protection, but that is unlikely because we failed to find a correlation between side-window UV-A blockage and year of vehicle. Interestingly, the 1990 Buick Riviera had a higher level of UV-A side-window protection than some of the newer luxury automobiles. Another limitation is that the present study was a correlational study of reduced UV-A protection in side windows and increased cataracts and skin cancer on the left side. If this association is shown to be a cause-and-effect relationship, then automakers may wish to consider increasing the level of UV-A protection in vehicle side windows, although the clinical relevance of these differences remains unknown at this time.

    The present study found that the front windshields of the automobiles tested provided a high and consistent level of UV-A protection. In contrast, the side windows of the automobiles tested provided variable levels of UV-A protection, which may expose drivers’ left eyes and left sides of faces to greater cumulative UV-A light. This exposure may increase the risk of cataract and skin cancer. It remains unknown whether this risk can be modified for each individual based on vehicle profile (whether or not sunglasses are worn) or other factors, such as time spent driving in a certain environment.

    Conclusions

    The present study may have a relevance beyond that of the risk of UV damage from driving automobiles. It brings awareness of the other types of windows that make people vulnerable to the effects of the sun. These findings may also provide support for the recommendation that residential, commercial, and school glass windows have UV protection for adults and children alike.11

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    Article Information

    Submitted for Publication: June 13, 2015; final revision received March 24, 2016; accepted March 25, 2016.

    Corresponding Author: Brian S. Boxer Wachler, MD, Boxer Wachler Vision Institute, 465 N Roxbury Dr, Ste 902, Beverly Hills, CA 90210 (info@boxerwachler.com).

    Published Online: May 12, 2016. doi:10.1001/jamaophthalmol.2016.1139.

    Conflict of Interest Disclosures: The author has completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

    Additional Contributions: I would like to acknowledge the contributions of Micaela Boxer Wachler, who assisted with data collection for this study.

    References
    1.
    Chylack  LT  Jr.  Mechanisms of senile cataract formation.  Ophthalmology. 1984;91(6):596-602.PubMedGoogle ScholarCrossref
    2.
    Chang  C, Murzaku  EC, Penn  L,  et al.  More skin, more sun, more tan, more melanoma.  Am J Public Health. 2014;104(11):e92-e99.PubMedGoogle ScholarCrossref
    3.
    Butler  ST, Fosko  SW.  Increased prevalence of left-sided skin cancers.  J Am Acad Dermatol. 2010;63(6):1006-1010.PubMedGoogle ScholarCrossref
    4.
    Paulson  KG, Iyer  JG, Nghiem  P.  Asymmetric lateral distribution of melanoma and Merkel cell carcinoma in the United States.  J Am Acad Dermatol. 2011;65(1):35-39.PubMedGoogle ScholarCrossref
    5.
    Hirvelä  H, Luukinen  H, Laatikainen  L.  Prevalence and risk factors of lens opacities in the elderly in Finland: a population-based study.  Ophthalmology. 1995;102(1):108-117.PubMedGoogle ScholarCrossref
    6.
    Bernstein  EF, Schwartz  M, Viehmeyer  R, Arocena  MS, Sambuco  CP, Ksenzenko  SM.  Measurement of protection afforded by ultraviolet-absorbing window film using an in vitro model of photodamage.  Lasers Surg Med. 2006;38(4):337-342.PubMedGoogle ScholarCrossref
    7.
    Abraham  AG, Cox  C, West  S.  The differential effect of ultraviolet light exposure on cataract rate across regions of the lens.  Invest Ophthalmol Vis Sci. 2010;51(8):3919-3923.PubMedGoogle ScholarCrossref
    8.
    Foley  P, Lanzer  D, Marks  R.  Are solar keratoses more common on the driver’s side?  Br Med J (Clin Res Ed). 1986;293(6538):18.PubMedGoogle ScholarCrossref
    9.
    Castanedo-Cazares  JP, Ehnis-Pérez  A, Zúñiga-Yudiche  M, Torres-Alvarez  B.  Motor vehicles and ultraviolet exposure in Mexico [in Spanish].  Rev Invest Clin. 2012;64(6, pt 2):620-624.PubMedGoogle Scholar
    10.
    Tuchinda  C, Srivannaboon  S, Lim  HW.  Photoprotection by window glass, automobile glass, and sunglasses.  J Am Acad Dermatol. 2006;54(5):845-854.PubMedGoogle ScholarCrossref
    11.
    Edlich  RF, Winters  KL, Cox  MJ,  et al.  Use of UV-protective windows and window films to aid in the prevention of skin cancer.  J Long Term Eff Med Implants. 2004;14(5):415-430.PubMedGoogle Scholar
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