Masters of Health Magazine September 2018 - Page 22

A solution must be designed safely cognizant of the potential risk from the blue-light-hazard and exposing the retina to wavelengths in the range of high-energy-visible light (HEV) 415-455nm for any extended period.

The proposed solution recognizes and has design elements that observe these risks. There is a growing awareness in the cell biology community concerned with eye-radiation exposure that the current standards provide a context of measurement that is temporally too limited. ANSI/IESNA RP-27 and IEC/EN 62471 2008 limits exposure times in laboratory mammals measuring retinal damage from blue light to 10000 seconds (approximately 2.75 hours). Current eye-related research on blue-light-hazard employs cytological methods of observation that measure significant changes in retinal structure (under laboratory conditions) but over time frames of 36 hours or more when exposed to blue-LEDs with SPD in the range of high-energy-visible light (415-455nm).

It is noteworthy that whilst sunlight of course contains wavelengths of 415-455nm that researchers have identified as potentially hazardous to the retina, it is also rich in wavelength of 480nm which ensures maximal sustained pupillary constriction by virtue of the ipRGC response. White light LEDs typically have a trough in the SPD at 480nm so maximal pupillary constriction may not be afforded the eye to autonomically provide its own natural protection against the shorter blue wavelengths. Importantly, this author notes that more recent published laboratory research has identified retinal changes (measured in the laboratory) to HEV exposure at luminance levels within the expected range of human experience.

Consideration must be given also to the greater transparency of younger eyes and scenarios where this solution may be deployed (kindergartens, schools and offices). It is essential that protection of the retina from HEV is made a priority in this solution, particularly when offered as a therapeutic benefit. Equally importantly, any light source with a blue peak at 480nm should be tunable in order that the spectral power distribution and luminance can be altered to respect the natural systemic circadian rhythm. The blue peak should decrease over time essentially following the natural changes in the sun's spectrum consistent with the time between sunrise and sunset.

Design of the LED Spectral Power Distribution

Wavelength, Luminance and Time: an example of a tunable LED algorithm

The following figures provide an example of the spectral power distribution and luminance delivered over time that provides for the necessary stimulation to affect the required ipRGC/retinal dopamine response as well as the helping to sustain the more ideal sustained and reduced pupillery aperture.

It is worth also noting that there is strong support in the research literature to support the view that by reducing ‘high-order-aberrations’ of the retinal image, i.e. by making it as in-focus as possible, this will also assist the eye-brain processing to maintain a more ideal axial length.