Blind people with undamaged eyes may still register light non-visually for the [[purpose]] of [http://en.wikipedia.org/wiki/Circadian_rhythm circadian entrainment] to the 24-hour light/dark cycle. Light signals for this [[purpose]] travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.[http://en.wikipedia.org/wiki/Blindness] | Blind people with undamaged eyes may still register light non-visually for the [[purpose]] of [http://en.wikipedia.org/wiki/Circadian_rhythm circadian entrainment] to the 24-hour light/dark cycle. Light signals for this [[purpose]] travel through the retinohypothalamic tract, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.[http://en.wikipedia.org/wiki/Blindness] |