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Customize blue light protection for each patient
Considering an individual's general health issues gives optometrists an opportunity to collaborate with other health care professionals.
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Blue light has received so much bad press in the last 20 years that a clinician could, understandably, consider recommending blue-blocking filters to almost all patients. However, given that the visual systems of humans and other animals have evolved over tens of thousands of years in the presence of a lot of blue light, one could well reason that it could have some beneficial role in sustaining and maintaining life, despite its detrimental effects on visual acuity and contrast sensitivity.
Blue-blocking IOLs
The extent to which blue light – perhaps more appropriately labeled “short wavelength visible light” – interferes with visual function may be over-emphasized.
In a 2014 study, Lavric and Pompe looked for differences in visual function and macular changes in a group of 30 patients, each of whom had an intraocular lens that blocked both ultraviolet and blue light in one eye and an IOL that blocked only ultraviolet light in the other eye. The difference in mean best-corrected visual acuity between the eyes barely reached statistical significance. Ishihara and Farnsworth 100-hue color vision testing showed no difference between the groups, and no difference in contrast sensitivity was shown for any of the spatial frequencies tested.
The subjects were followed for more than 2 years, and no significant difference in macular changes was noted between the IOL groups. The authors stated that clinical evidence for macular protection by a blue-light filtering IOL is still lacking.
While filtering out blue light certainly has been shown to lower glare susceptibility under driving conditions (Gray et al.), whether a similar result would occur with polarized lenses was not tested.
Blue light and myopia
Liu and colleagues raised infant rhesus monkeys for 51 weeks under one of three lighting conditions: blue light (peak 455 nm), red light (peak 610 nm) and white light (color temperature 5,000 K). Refraction and biometric measures at 51 weeks showed that the monkeys raised in red light were about 1.50 D more myopic than either the monkeys raised in blue or white light. No significant difference was found between mean refractive error of the monkeys raised in blue vs. white light.
Patricia M. Cisarik
Combined with the recent epidemiological studies that show an inverse relationship between myopia and ocular sun exposure (McKnight et al. and Guggenheim et al.), these results suggest that exposure to visible light toward the blue end of the spectrum may be a factor in emmetropization.
Intrinsically photoreceptive RGCs
Another relatively recent discovery is that of a group of retinal ganglion cells (RGCs) that appears to play a lesser role in image processing and color perception but a greater role in light-mediated but nonvisual functions. The intrinsically photoreceptive retinal ganglion cells, or ipRGCs, of which there are at least five types, contain a photopigment called melanopsin. Unlike most of the ganglion cells in the retina, the ipRGCs do not send axons to the lateral geniculate nucleus; that is, they are not part of the “visual” pathway. Instead, their axons go to areas of the brain that regulate nonvisual photic behaviors, such as pupil responses, circadian rhythms, autonomic nervous system responses and hormonal levels.
The photopigment in these cells can respond to light over a range of wavelengths, but visible light toward the blue end is most easily captured by the photopigment (peak sensitivity to wavelength of 480 nm).
Circadian rhythms
In particular, the effect of blue light on circadian rhythms has generated recent interest because of the prevalence of sleep disorders in our modern society and their adverse effects on metabolic health. Exposure to light (especially blue, about 460 nm to 480 nm) suppresses melatonin release in the brain, while darkness increases melatonin release, making one sleepy. Thus, the timing of blue light exposure, such as late in the evening, can disrupt the normal circadian regulation of melatonin and contribute to sleep disorders in many people. Lack of sleep can adversely affect the immune system and contribute to depression.
Conversely, lack of exposure to blue light during the day, or decreased exposure over the course of the day (as occurs in the northern hemisphere in the winter) can contribute to a condition known as seasonal affective disorder (SAD), wherein affected individuals are depressed during the winter months.
A study by Roecklein and colleagues showed that patients with SAD had a decreased pupil response to blue light when compared with healthy controls. They concluded that SAD patients probably have a reduced sensitivity of the light input pathway to the nonvisual brain areas, which may explain why light therapy (generally, a full spectrum light that mimics sunlight) helps many of these patients.
Blue light: Good or bad?
So, is blue light exposure good for humans or bad? I would like to suggest that we start with the philosophy of, “Everything in moderation,” and then customize the recommendations for the individual patient, taking into consideration their visual demands, their health (physical, ocular and mental), their medications, their environments, their age and any specific tasks or goals they want or need to accomplish. This is part of the “art” of optometry.
For example: Should all of our cataract patients have UV- and blue-blocking intraocular lenses implanted? Probably not. If our patient drives a lot, such a lens may be in order to minimize glare. However, glare could also be reduced with a sun wear filter, thereby allowing blue light exposure at other times. If our patient frequently loses eye wear, then maybe a recommendation for the more permanent filtered implant would be best.
Another example: Should we recommend that all people, regardless of age, wear sunglasses that block UV and blue light whenever outdoors in daylight? Probably not – not even as a blanket recommendation for aging eyes, because we would like to avoid aggravating sleep disorders and depression. Remember, the elderly generally have smaller pupils, anyway, so less light will get in. However, we can recommend that they use their sun protective lenses between 10 a.m. and about 3 p.m., when the sunlight is more intense. Otherwise, if they are comfortable, not wearing sun protective lenses may be OK. Additionally, polarized lenses may help reduce glare.
If an individual patient has cataracts or macular degeneration (or a strong family history of macular degeneration, especially with profound vision loss), our advice may lean more toward the minimization of UV and blue light exposure. We still, however, have to consider our recommendations in the context of the patient’s general health issues (sleep disorders, depression, metabolic disorders), which gives us a great opportunity to work with other health care practitioners to maximize the quality of life for our patients.
- References:
- Gray R, et al. J Cataract Refract Surg. 2012; 38(5):816-822.
- Guggenheim JA, et al. Invest Ophthalmol Vis Sci. 2012;53(6):2856-2865.
- Lavric A, et al. Optom Vis Sci. 2014;91(11):1348-1354.
- Liu R, et al. Invest Ophthalmol Vis Sci. 2014;55(3):1901-1909.
- Lucas RJ, et al. Trends Neurosci. 2014;37(1):1-9.
- McKnight CM, et al. Am J Ophthalmol. 2014;158(5):1079-1085.
- Nedeltcheva AV, et al. Curr Opin Endocrinol Diabetes Obes. 2014;21(4):293-298.
- Roecklein K, et al. Psychiatry Res. 2013;210(1):150-158.
- For more information:
- Patricia M. Cisarik, OD, PhD, is an associate professor at Southern College of Optometry in Memphis, Tenn. She can be reached at pcisarik@sco.edu.
Disclosure: Cisarik reports no relevant financial disclosures.