Achromatopsia is a predominantly stable/slowly progressive retinal dystrophy characterised by the lack of function in all three classes of cone photoreceptors (S-cones, M-cones and L-cones) from birth or early infancy.

Achromatopsia is a inherited retinal condition where the cone photoreceptors are predominantly affected. Patients tend to have poor colour vision, reduced visual sharpness and light sensitivity. Vision may be better in dim or dark situations as the rod photoreceptors are usually not affected.

Infantile nystagmus syndrome (INS) is an umbrella term used to describe different forms of infantile nystagmus (with or without sensory defects) characterised by an increasing slow phase velocity.