Loss of cells in outer nuclear layer. Nuclei in individual rows in the outer nuclear layers were counted in retinal sections at the indicated ages for mice of different genotypes. ♦, +/+; ▴, +/hrhoG(H); ⋄, +/hrhoG; •, +/hrhoG (modified Fvb background); ▵, hrhoG(H)/hrhoG(H); ▿, hrhoG/hrhoG(H); ○, hrhoG/hrhoG.