CXCR5 and blindness (disorder): While the well characterized photoreceptors BLR1 and BLR2 (putatively as BLR1–BLR2 photoreceptor-complex) are predicted to mediate the reception of the light signal, this study reveals that ENVOY is involved in the conditional adaptation to light, because lack of functional ENVOY does not result in blindness but leads to an altered gene expression pattern of light-regulated genes.