Inclusion Criteria (Both Eyes) * clinical diagnosis of achromatopsia * 6-12 years of age * ≥ 18 years of age * confirmed mutation in CNGA3 * BCVA ≥ 20/400 * a minimal outer nuclear layer thickness of 10µm at 3° eccentricity (normal = 38±6µm) * ability to understand and willingness to consent to study protocol * no infection with Human Immundeficiency Virus (HIV) * Male patients must agree to use condoms during the first 6 months post treatment. * Female patients of childbearing potential must agree to use an effective method of birth control during the first 6 months post treatment. * negative pregnancy test in women with childbearing potential (a woman who is two years post-menopausal or surgically sterile is not considered to be of childbearing potential) Exclusion Criteria * any other retinopathy due to other diseases e.g. (but not limited to) arterial hypertension, trauma or acquired inflammatory diseases (uveitis serology) , retinopathy of the premature * systemic conditions (e.g. coronary heart disease, congenital/genetic conditions, autoimmune disorders) which may affect study participation or outcome measures * current or recent participation in other study or administration of biologic agent within the last three months * recent (6 months) ocular surgery, intravitreal or subretinal implantation of a medical device * known sensitivity to any compound used in the study * contraindications to systemic immunosuppression * subject/partner of childbearing potential unwilling to use adequate contraception for six months after dosing * nursing or pregnant female subject women * any other cause that, in the investigator's opinion, renders potential subjects not suitable for the study * mutations in another achromatopsia gene * contraindications in view of the planned surgery (e.g. anaemia Hb\<8g/dl, severe coagulopathy, severe blood pressure fluctuations) including intolerance and contraindications to general anaesthesia * ocular opacity and mature cataract * ocular infection with herpes simplex virus in medical history * history of ocular malignancies * disorders of the internal retina (e.g. retinal detachment in the patients history) * glaucoma defined as damage of the optic nerve * vascular retinal occlusion * history of poorly controlled (HbA1c \> 7%) Diabetes Mellitus type 1 or type 2 * patients treated with systemic corticoids within 14 days prior inclusion * systemic illness or medically significant abnormal laboratory values \>3 UNL in blood analysis including renal and hepatic functions at inclusion * absence of vision on the other contralateral eye * contraindication to pharmacological mydriasis (e.g. history of angle block glaucoma)