In our daily lives, exposure to artificial lighting are increasing with the introduction of light-emitting diodes (LEDs) in our homes, workplaces and cities. This rapidly changing environment raises major concerns about photo-toxicity to the retina, as exposure to light is an identified risk factor for the development of age-related macular degeneration (AMD). In this disease, cone photoreceptors degenerate while the retinal pigment epithelium (RPE), at the contact of cones, accumulates photo-toxic compounds. Therefore, both cell types can be cell target for phototoxicity but light toxicity has never been characterized spectrally on cone photoreceptors.

In this study, scientists made this characterization by defining which wavelengths are toxic to cone photoreceptors either at a given intensity or at intensities of sunlight received on the retina

The researchers purified cone photoreceptors from the pig retina, because they have a size and a morphology very close to those of the human retina. Cells were exposed to 10nm wavelength bands from 390 to 510 nm, plus the 630 nm band. For a given intensity, the most toxic wavelengths are in the visible range, close to UV whereas they shift to blue-violet light (425-445 nm) when the cells are exposed to a solar source filtered by the optics of the eye. The spectral sensitivity to the toxic light suggests that light toxicity cannot be attributed to the visual pigment but rather to a porphyrin.

Light intensities used in this study are similar to those encountered on a sunny summer day in Paris. In addition, they are lower than those toxic to the retinal pigment epithelium. Therefore, this study indicates that cone photoreceptors are likely the first cell target for phototoxicity in AMD. It support the interest for filtering blue-violet light to prevent the pathologies of cone photoreceptors as AMD.

This publication "Phototoxic damage to cone photoreceptors can be independent of the visual pigment: the porphyrin hypothesis" has been published in Cell Death & Disease volume 11, Article number: 711 (2020).