Retinoid-binding protein which shows highest affinity for all-trans retinol. Can also bind all-trans forms of retinoic acid and retinal, but has lower affinity for cis form retinoids. Required in retinal pigment cells for rhodopsin biosynthesis. Strongly expressed in retina, where it may localize to pigment cells. Also detected in lamina, medulla, and optic lobes. Detected from the third larval instar onwards, with maximal expression levels in adult flies. Visual response is impaired, characterized by abnormal electroretinogram (ERG) recordings which show loss of the prolonged depolarization afterpotential which normally occurs in response to blue light. Expression levels of the opsins Rh1 and Rh4 are severely decreased.