Colour vision deficiency and inherited retinal disease: Viva

This is a branching oral built to probe the reasoning that holds the colour vision test and the inheritance at the centre, the electroretinography and the molecular genetics of the inherited retinal disease, and to expose the candidate who has memorised the headline of the gene therapy without the safety-critical corners. The questions escalate from the framing to the Ishihara test, the inheritance, the retinitis pigmentosa and the Leber congenital amaurosis, with deliberate probes into the choroideremia and the gene therapy. [6]

Opening question: framing the problem

The examiner opens with the boy who confuses the red and the green and asks: how do you frame this problem, and what is your first step? [6]

A strong answer names the congenital red-green colour vision deficiency, confirms the finding with the formal Ishihara test, and states that the first step is the exclusion of the acquired cause and the reassurance. [6]

Model answer. This boy has the congenital red-green colour vision deficiency, the common X-linked recessive trait, and the first step is to confirm it with the formal Ishihara test, to exclude the acquired cause by confirming the normal acuity, the full fields and the healthy fundus, and to reassure the family that the condition is stable, inherited and benign. The normal acuity and the healthy fundus distinguish it from the acquired defect and the inherited retinal dystrophy. [6]

Probe one: the Ishihara test

The examiner presses: describe the Ishihara test, and tell me its limitation. [6]