ACROMATOPSIA
Acromatopsia 2 - ACHM2
Acromatopsia 3/1 - ACHM3/1
Acromatopisa 4 - ACHM4
Acromatopsia 5 - ACHM5/OCD4
Acromatopsia incompleta - BCM
Cecità ai colori - GeneReviews ACHROMATOPSIA
Clinical characteristics
Achromatopsia is characterized by reduced visual acuity, pendular nystagmus, increased sensitivity to light (photophobia), a small central scotoma, eccentric fixation, and reduced or complete loss of color discrimination. All individuals with achromatopsia (achromats) have impaired color discrimination along all three axes of color vision corresponding to the three cone classes: the protan or long-wavelength-sensitive cone axis (red), the deutan or middle-wavelength-sensitive cone axis (green), and the tritan or short-wavelength-sensitive cone axis (blue). Most individuals have complete achromatopsia, with total lack of function of all three types of cones. Rarely, individuals have incomplete achromatopsia, in which one or more cone types may be partially functioning. The symptoms are similar to those of individuals with complete achromatopsia, but generally less severe.
Hyperopia is common in achromatopsia. Nystagmus develops during the first few weeks after birth followed by increased sensitivity to bright light. Best visual acuity varies with severity of the disease; it is 20/200 or less in complete achromatopsia and may be as high as 20/80 in incomplete achromatopsia. Visual acuity is usually stable over time; both nystagmus and sensitivity to bright light may improve slightly. Although the fundus is usually normal, macular changes (which may show early signs of progression) and vessel narrowing may be present in some affected individuals. Defects in the macula are visible on optical coherence tomography.
Diagnosis/testing
The diagnosis of achromatopsia is established in a proband through clinical and family history, examination for nystagmus, visual acuity testing, color vision assessment, and fundoscopic examination. If achromatopsia is suspected, additional testing may include optical coherence tomography, fundus autofluorescence, visual fields, and ERG. Identification of biallelic pathogenic variants in CNGB3, CNGA3, GNAT2, PDE6C, ATF6, or PDE6H confirms the clinical diagnosis and allows for family studies.
Management
Treatment of manifestations: Dark or special filter glasses or red-tinted contact lenses to reduce photophobia and potentially improve visual acuity; low vision aids; preferential classroom seating for children; occupational aids.
Surveillance: Ophthalmologic examination every six to 12 months for children and every two to three years for adults.
Genetic counseling
Achromatopsia is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the pathogenic variants have been identified in the family.
