The rhabdomeres of 1 day old mutant flies are virtually normal. 7 day old mutant flies show a severe decrease in the average size of the peripheral rhabdomeres, and the microvilli of most peripheral rhabdomeres are severely shortened (although they are not detached). 2 week old mutant flies contain detached and broken microvilli in peripheral rhabdomeres, and the overall length of the microvilli is much shorter than normal. The cell bodies of the peripheral rhabdomeres are severely shrunken. The central R7 rhabdomeres contain normally attached microvilli, although many of the rhabdomeres are deformed.

Mutant 7 day old flies raised completely in the dark have some irregularly shaped and/or smaller rhabdomeres, but the phenotype is much milder than mutant flies exposed to light.

Electroretinogram responses of 1 day old mutant flies have a smaller amplitude than those of wild-type flies. Electroretinogram responses of 7 day old mutant flies have a smaller amplitude and slower termination than those of wild-type flies.

In whole-cell current recordings in the dark, mutant photoreceptors have a normal background inward current and reversal potential. The mutant photoreceptors show a smaller light response compared to wild type.