Achromatopsia

Achromatopsia, also known as total color blindness, is a medical syndrome that exhibits symptoms relating to at least five conditions. The term may refer to acquired conditions such as cerebral achromatopsia, but it typically refers to an autosomal recessive congenital color vision condition, the inability to perceive color and to achieve satisfactory visual acuity at high light levels, typically exterior daylight. The syndrome is also present in an incomplete form which is more properly defined as dyschromatopsia. It is estimated to affect 1 in 30,000 live births worldwide.The syndrome is frequently noticed first in children around six months of age by their photophobic activity 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).The congenital forms of the condition are considered stationary and do not worsen with age.Acquired achromatopsia or dyschromatopsia is a condition associated with damage to the diencephalon—primarily the thalamus of the mid brain—or the cerebral cortex (the new brain), specifically the fourth visual association area, V4 which receives information from the parvocellular pathway involved in colour processing.The hemeralopic aspect of achromatopsia can be diagnosed non-invasively using electroretinography. The response at low (scotopic) and median (mesotopic) light levels will be normal but the response under high light level (photopic) conditions will be absent. The mesotopic level is approximately a 100 times lower than the clinical level used for the typical high level electroretinogram. When as described, the condition is due to a saturation in the neural portion of the retina and not due to the absence of the photoreceptors per se.There is generally no treatment to cure achromatopsia. However, dark red or plum colored filters are very helpful in controlling light sensitivity.Achromatopsia is a relatively uncommon disorder, with a prevalence of 1 in 30,000 people.Books