Lenses protecting against photosensitivity violate international driving regulations

To the Editors: The insightful review on visually provoked seizures by Fisher et al.1 provides relevant and valuable information on a broad range of aspects related to photosensitivity and epilepsy. This includes potential real-life trigger situations, such as a risk that may be posed by flickering light at frequencies associated with a high susceptibility to photoparoxysmal responses when driving along an avenue at dawn or sunset. As a nonpharmacological treatment option to protect patients with photoparoxysmal responses, dark lenses and blue lenses—particularly the Zeiss Z1 blue lens—are discussed due to their ability to reduce or even abolish photosensitivity, as demonstrated in several studies (e.g., Takahashi and Tsukahara,2 Capovilla et al.3). In particular, the review notes that, when driving a car, tinted glasses with reduced light transmission are recommended. At the same time, however, the authors emphasize that lenses impairing the perception of orange traffic signals should be avoided. We would like to highlight this latter point, as it is highly relevant when considering the use of tinted lenses in photosensitive patients who drive. Dark sunglasses are unsuitable for driving at sunset or during nighttime due to their reduced light transmission.4 In addition, the Z1 lens—and blue lenses in general—substantially alter the spectral composition of transmitted light by selectively attenuating longer wavelengths of the visible spectrum. This results in a marked reduction in the visibility of red and orange visual stimuli. Such stimuli are critical in traffic, particularly for the recognition of traffic lights as well as the brake lights and taillights of vehicles (Figure 1). Attenuation of red light intensity may delay stimulus recognition and consequently prolong reaction times while driving. Therefore, although these lenses may exert beneficial effects in reducing photosensitivity, they may simultaneously increase the risk of traffic accidents. Accordingly, blue lenses—and especially Z1 lenses, which have the strongest evidence for suppressing photosensitivity—are not considered suitable for driving according to the International Organization for Standardization (ISO 12312-1:2022). Prescribing colored or dark lenses for patients with purely visually provoked seizures who may be legally permitted to drive once the triggering stimulus is suppressed therefore requires careful consideration of both their beneficial effects and potentially associated risks, as well as implications with regard to driving regulations. Open Access funding enabled and organized by Projekt DEAL. None of the authors has any conflict of interest related to this letter to disclose. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. ISO 12312-1:2022, p. 6 (Requirements for road use and driving): Filters suitable for road use and driving shall additionally meet the following two requirements: Spectral transmittance. The spectral transmittance of filters suitable for road use and driving for wavelengths between 475 and 650 nm shall be not less than 0.20 τv D65. Detection of signal lights. The relative visual attenuation quotient Q of filters of categories 0, 1, 2 and 3 suitable for road use and driving shall be not less than 0.80 for red signal light and not less than 0.60 for yellow, green and blue signal lights.