REFRACTIVE EWAP SEPTEMBER 2023 23 Chromatic aberration can significantly degrade visual quality. The proper chromophore can potentially lessen the negative effects of chromatic aberration from a lens with low Abbe number (high chromatic aberration) by filtering out high energy, short wavelength light that may be out of focus due to the high dispersion. Nevertheless, starting with a high Abbe number material with low dispersion and low chromatic aberration is still the preferred approach. Scotopic vision requires participation of rod photoreceptors, which are sensitive to blue light. Filtering out that blue light can reduce scotopic or low light vision. The ideal chromophore would filter violet and not blue light, protecting scotopic vision while reducing dysphotopsias. When looking at retinal photoprotection, Dr. Chang said, the shorter the wavelength, the higher the energy, and the more damage it can do. In general, wavelengths in the range of 410 nm and below have increasingly greater toxicity. Ultraviolet light is 380 nm and below. “Both higher energy violet and blue light can have some potential phototoxicity effects,” he said. But since blue light can impact functional vision, you would prefer to filter it with a pair of sunglasses. You want to make sure you’re only blocking the primarily negative wavelengths in the eye. Finally, with circadian rhythm, Dr. Chang said there are the intrinsically photosenstive retinal ganglion cells, which have sensitivity in the blue light spectrum. When you wake up in the morning to a lot of blue light, this increases melanopsin production and inhibits melatonin production. The idea is to reduce blue light exposure as the day goes on to help maintain circadian rhythm. Blocking blue light may thus interfere with circadian rhythm function. Looking at the absorption spectrum, the AcrySof IOL (Alcon) blue light-filtering chromophore filters up to a third of blue light wavelengths, and because it has a broad spectrum range, filtration depends on the IOL power, so it’s not consistent. The Johnson & Johnson Vision violet light-filtering chromophore has a steep peak. More importantly, you’re keeping blue and filtering violet, Dr. Chang said. The Alcon chromophore filters out blue light, which potentially could affect scotopic vision and circadian rhythm, but it doesn’t filter out all of the high energy violet light, with up to 25% of the 410 nm violet still being transmitted vs. 0% for the Johnson & Johnson Vision chromophore. In a presentation that looked at the theoretical comparative impact of a violet vs. blue light filter, Dr. Chang shared data showing the Johnson & Johnson Vision violet light filter having less decrease in scotopic vision, less impact on circadian rhythm, and the same amount of macular photoprotection. 5 Dr. Waring said he has largely moved to violet filtration for presbyopia - correcting IOLs, but he added that InteliLight is reserved for diffractive presbyopia - correcting IOLs. Johnson & Johnson Vision is currently the only manufacturer to offer this, and it is not offered in a monofocal or monofocal toric. “More patients are seeking presbyopia correction, but those who are not a candidate would still benefit from violet filtration in the monofocal and monofocal toric.” Dr. Waring emphasized that the benefit of violet filtration for low light contrast sensitivity is typically the most challenging visual environment, in particular with diffractive presbyopia- correcting IOLs. The violet filtration helps by reducing light scatter and improving image quality, improving low light contrast, improving low light reading performance, and mitigating and reducing dysphotopsias, he said. In terms of patients for whom high energy light filtering would be most beneficial, Dr. Chang said that while there are many potential benefits, demonstrating them clinically can be challenging. “Traditional clinical vision tests are simply not designed to study the visual impact of high energy light filters, much less differentiate them.” As an example, the emission spectra of lighting or glare sources used in vision tests are not routinely characterized. Warmer vs. cooler lights, fluorescent vs. LED lights, white vs. monochromatic light may all impact testing results, particularly when considering the effect of a chromophore, yet few studies even consider these factors. There have been some population-based epidemiological studies, but it’s hard to isolate the impact of the chromophore alone. “Part of the problem is blue light-filtering has become a marketing concept,” he said. “The challenge is to address the topic with enough specificity for relevance without so much complexity that people are unable to follow.”
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