‘Good’ and ‘bad’ light filtering and IOLs

A study of violet- and blue-light filtering (VLF and BLF, respectively) chromophores in intraocular lens (IOL) implants has concluded that VLFs block the harmful light that contributes to reactive oxygen species (ROP). However, the team, led by Dr Daniel Chang at Empire Eye and Laser Center, California, cautioned that BLFs can exclude parts of the spectrum that are essential to human health.

While all IOPs block ultraviolet light, Chang’s team sought to establish the wavelengths, if any, within the 380-500nm spectrum that should be filtered. They concluded that the ideal filter permits blue light in the range of 450-500nm (allowing near-normal functioning of melanopsin, which impacts circadian rhythms and sleep quality) but blocks violet light below 450nm to prevent ROS formation.

The study adds to the findings of Associate Professor Laura Downie et al at The University of Melbourne, who stated in a 2018 paper that, “Short‐wavelength visible light can induce retinal phototoxicity and BLF-IOLs have been suggested to impart retinal protection and potentially prevent the development and progression of age‐related macular degeneration (AMD).”

In a separate study, published by the University of Pittsburgh, researchers led by Dr John Griepentrog said that, “Analysis of older adults undergoing bilateral cataract surgery found that IOLs that transmit the entire visible spectrum (conventional IOL), including the short wavelength blue spectrum are associated with a clinically relevant lower risk of death by comparison to BLF-IOL… Although not definitive, these data contribute to the biologic plausibility of our overarching hypothesis that perhaps the spectrum of light restored with cataract surgery is a critical determinant of health.”

The effect of age upon the way the human crystalline lens naturally filters this part of the spectrum is another important factor. Griepentrog et al said, “Notable differences do exist between BF-IOL and the crystalline lens of a child, of a middle-aged adult, and of an elderly person. The BF-IOLs we studied impede the transmission of 450nm light by more than 50%, with one approximating a 60% reduction; at these shorter wavelengths the filtration is of considerably greater magnitude than the lens of a child and, for some, exceed that of a 50-year-old adult.”