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.
One example of a pressure phosphene is demonstrated by gently pressing the side of ones eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.Another common phosphene is "seeing stars" from a sneeze, laughter, a heavy and deep cough, blowing of the nose, a blow on the head or low blood pressure (such as on standing up too quickly or prior to fainting). It is possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic (such as from low oxygenation or lack of glucose) stimulation of neurons of the visual cortex or of other parts of the visual system.Less commonly, phosphenes can also be caused by some diseases of the retina and nerves, such as multiple sclerosis. The British National Formulary lists phosphenes as an occasional side effect of at least one anti-anginal medication. The name "phosphene" was coined by J. B. H. Savigny, better known as the ships surgeon of the wrecked French frigate Méduse. It was first employed by Serre dUzes to test retinal function prior to cataract surgery. Electrical stimulation
Phosphenes have been created by electrical stimulation of the brain, reported by neurologist Otfrid Foerster as early as 1929. Brindley and Lewin (1968) inserted a matrix of stimulating electrodes directly into the visual cortex of a 52-year-old blind female, using small pulses of electricity to create phosphenes. These phosphenes were points, spots, and bars of colorless or colored light.