PDE6C and achromatopsia: The low proportion of patients with FAF Groups 3 and 4, and OCT Grades 3 and 4 (Table 1) in our study, can support the speculation that those stages are short transitional state of the disease natural history, in contrast to CNGB3-, CNGA3-, and PDE6C-achromatopsia where Grade 4 is more common.29