Blue cone monochromatism (BCM) is a recessive X-linked disease characterized by severely impaired color discrimination, low visual acuity, nystagmus, and photophobia, due to dysfunction of the red (L) and green (M) cone photoreceptors. BCM is as an incomplete form of achromatopsia. The disease is blue cone monochromacy (MONDO_0010563, a Monarch Disease Ontology identifier). Also known as: S cone monochromacy, S cone monochromatism, X-linked incomplete achromatopsia, atypical X-linked achromatopsia, blue cone monochromacy, X-linked recessive, blue cone monochromatism, color blindness, blue monocone monochromatic type, colour blindness, blue monocone monochromatic type.