Severe reduction of the ability to see. On the 6m visual acuity scale, severe reduction is defined as less than 6/60 but at least 3/60. On the 20ft visual acuity scale, severe reduction is defined as less than 20/200 but at least 20/400. On the decimal visual acuity scale, severe reduction is defined as less than 0.1 but at least 0.05. The phenotype is Severely reduced visual acuity (HP_0001141, a Human Phenotype Ontology id). Also known as: Marked vision impairment, Severe reduction in visual acuity, Severe vision loss, Severe visual impairment, Severe visual loss, Severely impaired vision.