Achromatopsia or ACHM is a condition where the patient is unable to perceive color. Although this name may also be used to refer to acquired defects such as cerebral achromatopsia or color agnosia, it normally refers to a congenital disorder of the vision which is autosomal recessive in nature. It can also be called rod monochromacy or total inborn color blindness. Patients with this kind of disorder manifest total absence of the cone cell activity through electroretinography. At least 4 causes are listed as congenital ACHM: ACHM2 and ACHM3; the third type is a cone photoreceptor transducin called GNAT2, ACHM4; the last cause is still unknown.