Photoreceptors in the eyes of porin^G2294 homozygous adults have not gross morphological defects. However, electroretinograms (ERGs) and intra-cellular recordings of the response of these photoreceptors to white light stimulation show significant differences from wild-type. In ERGs, the peak amplitude as a function of stimulus intensity is consistently higher than wild-type for all but the lowest intensity stimulation, but the response then declines to a much lower steady than seen in wild-type. In contrast, the latency of response (the time between stimulus and response) is normal. Comparable results are seen with intra-cellular recordings from photoreceptors. The membrane potential of these photoreceptors is normal in the absence of stimulus and returns to normal levels following termination of stimulus at the same rate as wild-type.