To the editor

We read with interest the article by Picaud and colleagues1 in the October issue of Nature Medicine. Evidence of rod and cone photoreceptor rescue by 1-cis diltiazem was quantified using techniques of immunohistochemistry, electrophysiology and photoreceptor counting. Of note, the authors described a considerable photoreceptor rescue as demonstrated by opsin antibody staining, but only a moderate rescue as demonstrated by photoreceptor cell counts.

We have previously shown that an antibody against opsin that recognizes the N terminal of the opsin molecule (similar to the antibody used by Picaud et al.) labeled only the rod outer segments but not the perikarya of normal rod cells. However, in degenerating phoreceptor cells the rod perikarya were also labeled2. We believe that the immunolabeling noted in this study1 might represent degenerating photoreceptor cells and not surviving cells as claimed.