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Visual Acuity OSCE Assessment Quiz

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A 24-year-old woman says colours look duller through her left eye and that the eye hurts when she moves it. Each eye is tested separately with Ishihara plates in good light, wearing her usual reading glasses. She reads the first screening plate with both eyes. With the right eye she reads all the remaining plates correctly, but with the left eye she misses several and says red objects look washed out compared with the right. Which interpretation is most appropriate?

A problem with visual acuity rather than colour vision, because her reading glasses leave the left eye unable to resolve the dot patterns Normal variation between the eyes, because the right eye is normal and the first plate was read with both eyes An acquired colour vision defect in one eye; the red desaturation points to optic nerve disease such as optic neuritis A congenital red-green colour deficiency, because the first plate excludes an acquired cause and the left eye is simply affected more A left retinal problem, because the missed plates and red desaturation localise the defect to the retina rather than the optic nerve

A A problem with visual acuity rather than colour vision, because her reading glasses leave the left eye unable to resolve the dot patterns
B Normal variation between the eyes, because the right eye is normal and the first plate was read with both eyes
C An acquired colour vision defect in one eye; the red desaturation points to optic nerve disease such as optic neuritis ✓
D A congenital red-green colour deficiency, because the first plate excludes an acquired cause and the left eye is simply affected more
E A left retinal problem, because the missed plates and red desaturation localise the defect to the retina rather than the optic nerve

The answer is C: An acquired colour vision defect in one eye; the red desaturation points to optic nerve disease such as optic neuritis

Explanation

Why C is correct

See Colour Vision. Option C is correct. Ishihara plates are circles of coloured dots that hide a number in a pattern of colour. The first plate is a test plate that everyone can read, including people with colour blindness, so reading it shows that the patient has understood the task and can see the dots well enough. This woman reads it with both eyes, then reads every other plate correctly with her right eye but misses several with her left. She also says red objects look washed out in the left eye, which is called red desaturation. A change that is new, one-sided and painful on eye movement points away from a lifelong inherited defect and towards an acquired colour defect from optic nerve disease, such as optic neuritis, which is inflammation of the optic nerve. Ishihara plates mainly test red-green discrimination, red desaturation is checked separately by comparing a red target between the eyes, and neither on its own proves optic neuritis. A memory aid: if the first plate is read, the rest are valid.

First plate: a test plate that everyone can read, so reading it shows the patient understood the task.
Red desaturation: red objects look washed out in the affected eye.
Meaning: a new, one-sided change with pain on eye movement points to an acquired optic nerve defect such as optic neuritis.

Why the other options are incorrect

A. A problem with visual acuity rather than colour vision, because her reading glasses leave the left eye unable to resolve the dot patterns: Reduced acuity can make plates harder, but she read the first plate and the left eye misses colours while red looks washed out. Pain on eye movement is an optic nerve sign, not a refractive error.
B. Normal variation between the eyes, because the right eye is normal and the first plate was read with both eyes: A new one-sided change in colour perception with pain on eye movement is abnormal. The first plate confirms understanding; it does not make the left eye's failures normal variation.
D. A congenital red-green colour deficiency, because the first plate excludes an acquired cause and the left eye is simply affected more: Congenital red-green deficiency is present from birth and affects both eyes rather than one new painful eye. The first plate is read by everyone and does not exclude an acquired cause.
E. A left retinal problem, because the missed plates and red desaturation localise the defect to the retina rather than the optic nerve: Ishihara plates test colour discrimination but do not localise the defect to the retina. Red desaturation with pain on eye movement points to the optic nerve.

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What you will practise

More questions from this set. Start the quiz to answer them and see each explanation.

1
When testing colour vision with Ishihara plates, what is the main purpose of the first plate?
2
What is the most appropriate way to finish a visual acuity assessment?

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