PDE6H encodes the gamma subunit of cone-specific cyclic GMP phosphodiesterase, a critical component of the phototransduction cascade in cone photoreceptors 1. PDE6H functions as a multisubunit enzyme that degrades cyclic GMP (cGMP) at specifically tuned rates, enabling signal amplification and transmission during visual perception 2. The protein is expressed specifically in cone outer segments and synaptic terminals, particularly in short and long/middle wavelength-sensitive cones 2. Pathogenic variants in PDE6H cause achromatopsia (color blindness), an autosomal recessive cone dysfunction syndrome affecting approximately 1 in 30,000 people 3. While CNGA3 and CNGB3 mutations account for up to 90% of achromatopsia cases, PDE6H mutations represent a significant genetic cause 3. PDE6H-associated achromatopsia presents at birth or early infancy with poor visual acuity, nystagmus, photophobia, and complete color vision loss, with variable cone subtype involvement 2. Notably, short-wave cone function is often more preserved than middle and long-wave cone function in PDE6H patients, suggesting differential cone vulnerability 2. Currently, no FDA-approved treatment exists, though multiple gene therapy approaches are under investigation in clinical trials 3. Additionally, PDE6H-derived promoters show promise for directing transgene expression in degenerating photoreceptors during advanced retinal disease stages 4.