AMBLYOPIA

dimness of vision that may be gradual or sudden in onset and may affect both eyes or one. It may be transient or permanent and can develop into blindness. The disorder may be caused by hysteria or by poisoning with ethyl or methyl (wood) alcohol, lead, arsenic, thallium, quinine, ergot, male fern, carbon disulfide, stramonium, or Cannabis sativa (Indian hemp, the plant from which marijuana and hashish are derived). One form of amblyopia, known as lazy eye, develops in 2 to 3 percent of the population before the age of 5 years. It is related to the suppression of vision in the macula (the centre of the retina) of one eye in order to avoid double vision due to impaired ability to fuse the images of both eyes into one image in the brain. See also strabismus; visual-field defect.