A study from the University of São Paulo evaluated the effectiveness of 12 models and found that only one met the safety limits established by an international organization.
Solar ultraviolet (UV) radiation contributes to various eye diseases, including cataracts and photokeratitis (a type of corneal inflammation). UV protection, primarily through sunglasses, can help delay or prevent these conditions. However, a study published in Research on Biomedical Engineering highlights significant shortcomings in the UV protection provided by sunglasses.
The study evaluated 12 different sunglasses models and found that only one met the International Commission on Non-Ionizing Radiation Protection (ICNIRP) safety limits for UV exposure.
Researchers from the Ophthalmic Instrumentation Laboratory at the São Carlos School of Engineering, University of São Paulo (EESC-USP) in Brazil, discovered that most lenses fail to meet at least one of the required safety standards. Moreover, their ability to block UV radiation diminishes over time, increasing the risk of eye damage.
Only one lens proved to be “optimal” because it completely blocked the radiation even after the aging test, which simulated 2,500 hours of sun exposure. The study does not mention the brands of glasses.
Understanding UV Radiation and Safety Standards
To ensure effective and comprehensive vision protection, scientists suggest that the industry adopt the ICNIRP limits as standard practice, thereby improving product quality.
The standards for certification of sunglasses and eye protection set limits for solar radiation filters at wavelengths between 280 and 380 nanometers (nm). The World Health Organization (WHO) and the International Commission set these limits between 280 and 400 nm. UV radiation is divided into three bands – UVC (100 to 280 nm), UVB (280 to 315 nm), and UVA (315 to 400 nm).
“We’ve been researching this in our lab since the 1990s. We’ve developed a science that can be used as a basis for establishing safety standards and norms. Today, we’re internationally recognized and cited by several authors in books and guidelines,” says Professor Liliane Ventura of the EESC-USP Department of Electrical and Computer Engineering, corresponding author of the article.
Ventura, who is coordinating a project supported by FAPESP, is also leading patent applications for two prototypes. One to measure the radiant exposure of the eye to direct, diffuse and reflected radiation from the inside of sunglass lenses. And another for testing the blocking of ultraviolet radiation in sunglasses sold to the public. Both are being processed by the USP Innovation Agency for submission to the National Institute of Industrial Property (INPI).
Ventura and her student at the time, Artur Duarte Loureiro, were recently granted a patent, also thanks to the support of FAPESP, for a technology that assesses the condition of sunglasses for driving by measuring the transmission of light at different wavelengths, such as green, yellow and red.
Researcher Mauro Masili, first author of the article and a member of the laboratory, highlights another study by the group, published in March 2024 in the journal Scientific Reports, which shows that regardless of the category of lenses – lighter or darker – glasses must guarantee UVA protection of over 86%. Lenses are categorized from 0 (lightest) to 4. A 0 is recommended for situations where there is little or no apparent sunlight. A 4, which is very dark, is not recommended for driving.
The results showed that less than 86% protection may actually increase the risk to eye health because the lenses allow more UV radiation to enter the eye. However, contrary to what has been argued in the scientific literature, this increase is not due to the dilation of the pupil caused by sunglasses, but rather to the widening of the field of vision.
“We put together a table that calculates UV, UVA, and UVB protection. In terms of pupil dilation, there are no bad glasses. They’ll all protect. But when we include field of vision magnification, that changes. In bright outdoor environments, the natural reflex is to try to close your eyes and wrinkle your forehead to reduce the light. Wearing sunglasses creates a darker environment, preventing the natural response and increasing the field of vision, which can lead to greater UV exposure if the lenses don’t provide adequate protection,” Masili explains.
Therefore, extending protection to up to 400 nm could minimize the risk of unnecessary exposure, according to the study.
Comings and goings
Since the late 1990s, when there were no standards for sunglass protection requirements in Brazil, Ventura and Masili have been helping the regulatory bodies to establish these guidelines, including the first analyses of optical characteristics that the professor conducted for the National Institute of Metrology, Quality and Technology (INMETRO) in 1997, based on international standards.
In 2003, the Brazilian Association of Technical Standards (ABNT) published NBR 15111, which established the physical characteristics of sunglasses for general use, such as driving and transit, with parameters similar to those in Europe. It established that protection in Brazil should be provided by filters between 280 and 380 nm.
The standard was revised in 2013, following research conducted by the group and supported by FAPESP, extending UV protection to 280-400 nm and increasing the irradiation resistance test from 25 hours to 50 hours. However, in 2015 it was withdrawn and replaced by ISO 12312-1, which reinstated the parameters of UV protection filters from 280 to 380 nm.
In 2016, another study conducted by the two researchers calculated solar radiation exposure in 27 Brazilian state capitals and 110 capitals in the northern hemisphere and showed that the test was ineffective in ensuring sunglass lens protection from UV radiation exposure.
Currently, there is no requirement for sunglasses to be certified for sale in Brazil. For example, for equipment used to drive vehicles, it is possible to perform the analysis using a spectrophotometer, equipment used for scientific purposes and handled by specialists.
Ventura says that she is developing a prototype for measuring radiant exposure of the eye, with a proposal for a sun protection factor label that could help consumers choose when shopping.
Reference: “Evaluation of solar ultraviolet blocking by sunglasses and their compliance with recommended safety limits” by Mauro Masili, Fernanda O. Duarte and Liliane Ventura, 26 November 2024, Research on Biomedical Engineering.
DOI: 10.1007/s42600-024-00390-3
The study was funded by the São Paulo Research Foundation.
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.
2 Comments
Which sunglasses were best?
Yes, that would be nice to know.