A patient reports that his vision has taken on an unusual colour tinge. Before revealing the answer, decide how you would assess whether this is chromatopsia.

Ask the patient to describe exactly what is affected: does the abnormal colouring involve the entire visual field pervasively, rather than a single object or a fleeting image, and does object identity and shape remain perceived normally throughout, with only the apparent colour affected. Establish which colour predominates, since a yellow, green, or red tinge are the most commonly described variants, differing from one another only in which colour predominates rather than in their underlying mechanism. Take a careful history of medication use and any toxic exposures, since chromatopsia is historically associated with particular toxic exposures and medication effects. Ask whether the tinge has resolved or changed since any suspected causative agent was stopped or adjusted, since it is usually reversible once the underlying cause resolves.