Achromatopsia, also known as Rod monochromacy, is a medical syndrome that exhibits symptoms relating to five conditions, most notably monochromacy. Historically, the name referred to monochromacy in general, but now typically refers only to an autosomal recessive congenital color vision condition. The term is also used to describe cerebral achromatopsia, though monochromacy is usually the only common symptom. The conditions include: monochromatic color blindness poor visual acuity and day-blindness. The syndrome is also present in an incomplete form that exhibits milder symptoms, including residual color vision. Achromatopsia is estimated to affect 1 in 30,000 live births worldwide. Signs and symptoms
The five symptoms associated with achromatopsia are:

Color blindness - usually monochromacy
Reduced visual acuity - uncorrectable with lenses
Hemeralopia – with the subject exhibiting photophobia
Nystagmus
Iris operating abnormalitiesThe syndrome is typically first noticed in children around six months of age due to their photophobia or their nystagmus. The nystagmus becomes less noticeable with age but the other symptoms of the syndrome become more relevant as school age approaches. Visual acuity and stability of the eye motions generally improve during the first six to seven years of life – but remain near 20/200. Otherwise the syndrome is considered stationary and does not worsen with age.If the light level during testing is optimized, achromats may achieve corrected visual acuity of 20/100 to 20/150 at lower light levels, regardless of the absence of color. The fundus of the eye appears completely normal.Achromatopsia can be classified as complete or incomplete.
In general, symptoms of incomplete achromatopsia are attenuated versions of those of complete achromatopsia. Individuals with incomplete achromatopsia have reduced visual acuity with or without nystagmus or photophobia. Incomplete achromats show only partial impairment of cone cell function. Cause
Achromatopsia is sometimes called rod monochromacy (as opposed to blue cone monochromacy), as achromats exhibit a complete absence of cone cell activity via electroretinography in photopic lighting. There are at least four genetic causes of achromatopsia, two of which involve cyclic nucleotide-gated ion channels (ACHM2, ACHM3), a third involves the cone photoreceptor transducin (GNAT2, ACHM4), and the last remains unknown.Known genetic causes of this include mutations in the cone cell cyclic nucleotide-gated ion channels CNGA3 (ACHM2) and CNGB3 (ACHM3), the cone cell transducin, GNAT2 (ACHM4), subunits of cone phosphodiesterase PDE6C (ACHM5, OMIM 613093) and PDEH (ACHM6, OMIM 610024), and ATF6 (ACHM7, OMIM 616517). Pathophysiology
The hemeralopic aspect of achromatopsia can be diagnosed non-invasively using electroretinography. The response at low (scotopic) and median (mesopic) light levels will be normal but the response under high light level (photopic) conditions will be absent. The mesopic level is approximately a hundred times lower than the clinical level used for the typical high level electroretinogram.