Comments and Conclusions
- Achromatopsia, also known as rod monochromatism, is a congenital ocular disorder characterized by total color blindness, low visual acuity, photophobia, and nystagmus. It is inherited as an autosomal recessive trait, with an estimated prevalence of 1/30,000.6
- Complete achromatopsia is associated with total lack of color vision due to the loss of functioning cone cells. Visual acuity for complete achromats is typically 20/200.6
- Incomplete achromatopsia, a rare variant of achromatopsia, is also associated with color vision loss but patients retain a small amount of color vision and slightly better visual acuity due to the presence of some functioning cone cells in the retina. The visual acuity of an incomplete achromat may range from 20/60 to 20/100.6
- To date, three genes have been shown to be responsible for achromatopsia. Mutations in the CNGA3 and CNGB3 genes, which encode alpha and beta subunits of the cone cyclic cGMP channel, a crucial component of phototransduction, cause achromatopsia in the majority of cases (20-30% CNGA3 and 40-50% CNGB3).7 In addition, mutations in GNAT2, which encodes cone specific alpha transducin, are a rare cause of achromatopsia (< 2%).6,7
- On OCT images of patients with achromatopsia, photoreceptor reflectivity disappears in the central retina.8 The PIL (a.k.a. IS/OS junction or ciliary layer) is often absent in an oval zone approximately 800 microns horizontally and 600 microns vertically.
- Although true pathognomotic OCT findings are rare, the hypo-reflective rectangle with sharply delineated borders is highly suggestive, if not pathognomonic, of achromatopsia. Of the first 8 achromats examined, 6 of them showed the “pathognomonic” sign in both eyes and 2 of them did not have the “pathognomonic” sign. A very small number (<1%) of patients with Stargardt disease appear to have a somewhat similar hyporeflective zone (see Case 7).4