Flies aged for 7 days under a light-dark cycle show no degeneration of rhabdomeres. When the retina of mutant animals are exposed to 0.5 sec pulses of orange light and the photoresponse measured, a corneal negative deflection is seen in the Electroretinogram (ERG). Upon termination of the light response there is a no delay in the deactivation of the light response. These flies also exhibit a normal, prolonged depolarisation afterpotential (PDA).