Tests on sunglasses show deficiencies in protection against ultraviolet rays

Solar ultraviolet radiation is one of the causes of a series of eye diseases, including cataracts and a type of corneal inflammation (photokeratitis), which can be delayed or prevented by using UV protection, with sunglasses being the most popular accessory for this function. However, a study published in the journal Research on Biomedical Engineering raises alarm bells by revealing shortcomings in this protection.

The study analyzed the effectiveness of 12 models of sunglasses and found that only one model met the safety limits for ultraviolet radiation exposure established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).      

Researchers from the Ophthalmic Instrumentation Laboratory at the São Carlos School of Engineering of the University of São Paulo (EESC-USP) in Brazil showed that the lenses do not meet at least one of the safety limits defined in the standards and that over time they lose some of their ability to block UV radiation, 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.

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 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.

About FAPESP

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the state of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration.