This will be a non-randomized, open-label, Phase 1/2 study of the safety and efficacy of AGTC-402, administered to one eye by subretinal injection in individuals with achromatopsia caused by mutations in the CNGA3 gene. The primary study endpoint will be safety and the secondary study endpoint will be efficacy.

This will be a non-randomized, open-label, Phase 1/2 study of the safety and efficacy of AGTC-402 administered to one eye by subretinal injection in individuals with achromatopsia caused by mutations in the CNGA3 gene. The primary study endpoint will be safety and the secondary study endpoint will be efficacy.

Subjects will be enrolled sequentially in six groups. Subjects in Groups 1, 2, 3, 4, and 5 will be at least 18 years of age and will receive varying dose levels of study agent. Subjects in Group 3a will be 6 to 17 years of age and will receive the same dose as Group 3. Subjects in Group 4a and 6 will be between 4 and 8 years of age. Subjects in Group 4a will receive the same dose as Group 4, and subjects in Group 6 will receive the maximum tolerated dose identified in Groups 1, 2, 3, 3a, 4, 4a, and 5.

Safety will be monitored by evaluation of ocular and non-ocular adverse events and hematology and clinical chemistry parameters. Efficacy parameters will include visual acuity, light discomfort testing, color vision, static visual field, ERG, adaptive optics retinal imaging, functional MRI (fMRI), color brightness test and OCT.

Inclusion Criteria:

1. Male or female subjects with documented mutations in both alleles of the CNGA3 gene;
2. Retinal disease consistent with a clinical diagnosis of achromatopsia;
3. At least 18 years of age for Groups 1, 2, 3, 4, and 5. At least 6 years of age for Group 3a, and and 4-8 years of age for Groups 4a and 6;
4. Able to perform tests of visual and retinal function;
5. Visual acuity in the study eye not better than 55 ETDRS letters (Snellen equivalent 20/80) based on the average of two examinations at the baseline visit;
6. Acceptable laboratory parameters;
7. For females of childbearing potential: A negative pregnancy test within 2 days before administration of study agent.

Exclusion Criteria include:

1. Best-corrected visual acuity difference between the two eyes of > 15 ETDRS letters (3 lines);
2. Evidence of degenerative myopia in the study eye;
3. Pre-existing eye conditions that would contribute to vision loss in either eye or increase the risk of subretinal injection in the study eye.