T his journal does not allow the space, figures, and referencing necessary to adequately respond to the factual errors and logical fallacies (eg, insufficient natural light exposure is not a problem reducible to the nature of cataract implants) in Mainster and associates. We feel, however, that it is important to offer a more balanced, albeit space-limited, view than simply regarding thousands of empirical studies across a range of disciplines and expert opinions as “hype” for the purpose of industry profits.
First, and most obviously, not all research on this topic is funded by Industry. The authors offer no actual evidence that this area is more biased or “hyped” than any other category of medical device. The authors suggest, tu quoque, that counterviews are inherently biased (presumably by many of the companies they consult for) mostly to sell “premium lenses.” Research, whether publicly or industry-funded, can be biased by many motivations ; the source of funding is only one of them and often not the most significant.
Mainster and associates make the basic argument that blue light–filtering (BLF) intraocular lenses (IOLs) (often called “natural” because they mimic the absorbance of an average young adult’s crystalline lens) are harmful and that implanting a perfectly clear lens in the older eye (more analogous to an infant) is a better strategy for optimal health and visual function. To make this somewhat counterintuitive argument, the authors first argue that blue light is healthy and therefore filtering is harmful. The blue light hazard (BLH) function is based on brief abnormally intense light exposures and, the authors argue, there is “no evidence” that long-term normal exposure leads to degenerative retinal change (note “long-term” starts in infancy, not at old age when a cataract is treated). This absence of evidence is, of course, based on the fact that long-term low-level light exposure is extremely difficult to obtain (especially prospectively): so, most scientists have to infer as they do with many issues that involve relating a single hard-to-quantify input to a complex endpoint that takes nearly a lifetime to develop. One can debate whether these inferences, which are based on a substantive confluence of evidence, are justified without assuming that they are a “marketing stratagem to alarm people.”
Mainster and associates also argue that BLF chromophores suppress blue light critical for good mental/physical health and for optimal scotopic and mesopic vision (note that even a BLF IOL means a significant increase in blue light when compared to the cataract it replaces). The authors omit an entire category of research on natural BLF chromophores like human macular pigment and the natural yellowing lens (ie, Would not the same argument apply?). A substantial proportion of short-wave light is often absorbed by these natural BLFs even in the very young eye (>1 log unit of optical density). This would be an issue if the visual system was simply a passive detector unable to adjust sensitivity but the system can, of course, adapt to varying light levels.
The authors also argue, again counterintuitively, that filtering blue light (unlike sunglasses) does not reduce glare issues focusing only on some laboratory tests of glare disability (GD) (they do not address other aspects of glare). The authors argue that a BLF cannot influence GD because the light source (eg, the sun) has “exactly” the same spectral characteristics as the target image that the subject is trying to see (eg, an object in the line of sight). The sun (like the xenon sources used in the psychophysical studies) is a common source of glare in the real world and contains a significant amount of blue light (as does blue sky light) and is off-axis. Target images in the real world (objects in the line of sight), are often mid- to long-wave (blue objects are relatively rare in nature ). It has been argued for nearly a century that natural intraocular BLF chromophores in many species evolved to reduce the deleterious effects of glare, and this has been shown in dozens of clinical trials.
Perhaps a more correct view is less ad hominem and does not lead to such a false dichotomy (hazard or hype). Blue light and BLF filtering is like light (and many aspects of lifestyle) in general: it is good, bad, or innocuous depending on the circumstances. Human vision is highly adaptable for this very reason: blue light filtering is just one additional strategy.
Funding/Support
This study received no funding. Financial Disclosures: Billy Hammond currently serves as a consultant for (and has conducted research funded by) Alcon Industries and Johnson and Johnson Vision Care. Lisa Renzi-Hammond serves as a consultant for (and has conducted research funded by) Johnson and Johnson Vision Care. All authors attest that they meet the current ICMJE criteria for authorship.
REFERENCES
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