Photosensitive pigments located in the retina translate light into electrical activity.
Most photopigments are located in the retinal rods and cones, rather than in ganglion cells but recently it was discovered that some retinal ganglion cells are themselves photosensitive, the ipRGCs.
They respond most strongly to deep blue light (475 and 485 nm). The ipRGCs are spread diffusely forming a photoreceptive net that samples the whole retina. IpRGCs project strongly to the 'biological clock', the suprachiasmatic nucleus (SCN) in the hypothalamus, which controls the body's diurnal rhythms.
This retinohypothalamic tract (RHT) input synchronises this clock to seasonally changing day length to maintain the correct phase relationship between daylight and the biological rhythms of endocrine, physiological and cognitive activity.
Dyslexia Research Trust - Vision & Coloured Filters
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