Failure of accommodation and convergence
Impaired accommodation and convergence are of limited diagnostic value since other clinical features are usually more prominent.
Causes - extrapyramidal disease, e.g. Parkinson's - tumours of the pineal region.
The Marcus Gunn pupil (pupillary escape)
Illumination of one eye normally produces pupillary constriction with a degree of waxing and waning (hippus).
When afferent transmission in the optic nerve is impaired, this 'escape' becomes more evident.
If the light source is 'swung' from eye to eye, dwelling 2-3 seconds on each, the affected pupil may eventually, paradoxically, dilate - a 'Marcus Gunn' pupil.
The swinging light test is a sensitive test of optic nerve retinal or macular disease.
damage but is also abnormal in
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