Blue-light hazard is defined as the potential for a photochemical induced retinal injury resulting from radiation exposure at wavelengths primarily between 400 nm and 500 nm.[4] The mechanisms for photochemical induced retinal injury are caused by the absorption of light by photoreceptors in the eye. Under normal conditions when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.[5][6] Absorption of blue light, however, has been shown to cause a reversal of the process where cells become unbleached and responsive again to light before it is ready. This greatly increases the potential for oxidative damage.[7] By this mechanism, some biological tissues such as skin, the lens of the eye, and in particular the retina may show irreversible changes induced by prolonged exposure to moderate levels of UV radiation and short-wavelength light.[citation needed]

[Retinal hazard from blue light emitting diode]
 
[Article in Japanese]
 
Koide R, Ueda TN, Dawson WW, Hope GM, Ellis A, Somuelson D, Ueda T, Iwabuchi S, Fukuda S, Matsuishi M, Yasuhara H, Ozawa T, Armstrong D.
 
Department of Ophthalmology, School of Medicine, Showa University, 2-14-19 Nishinakanobu, Shinagawa-ku, Tokyo 142-0054, Japan.
Abstract
 
PURPOSE: To compare the effect of exposure time from a blue(460 nm) light emitting diode(LED) on the morphology of the outer retina and determine conditions where damage occurs.
 
MATERIALS AND METHODS: Young adult rhesus monkeys were anesthetized, and received blue LED exposure from a modified slit-lamp. A 3 mm beam of 0.85 mW was imaged onto the retina through a lens positioned before the cornea and exposure damage was determined at time intervals for 12 to 90 min. Fundus photography, fluorescein angiography(FAG), retinal tomography(HRT), and s-cone electororetinogram(S-ERG) were recorded at baseline, 2, and 30 days.
 
RESULTS: Two days after 40 min exposure, there was a grey, discolored region, which was over-fluorescent in FAG, and an incresse in HRT and S-ERG corresponding to the site which was exposed to LED light. In histological examination at 30 days, the LED had caused produced a marked disruption of the disks of photoreceptor cells, damaged retinal pigment epithelium(RPE) apical villi, and a loss of RPE melanin after 90 min exposure.
 
CONCLUSION: A threshold level was found around 40 min. This morphological damage may impair function and continuous exposure to blue light is potentially dangerous to vision.