![]() ![]() Usually a cause cannot be found, but rarely this can affect people following an infection or surgery to the eye socket. In 1 in 500 people, the nerves that control pupil constriction in one eye do not work properly (Tonic or Adie’s pupil). In a fifth of people, the pupils are usually slightly different in size (‘physiological anisocoria’). Normally this system works well, without our being aware of it, but there are many ways in which control can be lost. The pupils also constrict when we look at near objects (for example when we read), which makes focusing easier. This makes a 20-times difference to the amount of light entering the eye. We all know that bright light makes the pupils smaller and dim light makes them larger. The pupils have muscles to constrict them (make them smaller) and muscles to dilate them (make them larger) and these are controlled by a network of nerves from the brain which works automatically. The pupil (the circular black area in the middle of the coloured part of the eye) is usually the same size as the pupil on the other side, and the two pupils usually react together (for example to light). Summary What are Abnormalities of the Pupil? Bilateral miosis with little or no constriction to direct light, but with apparently normal, pupil constriction to near targets.Horner syndrome that occurs very early in life can lead to iris heterochromia. ![]() Anhydrosis varies from the entire half face to a small patch on the forehead, depending on the location of the lesion.Anisocoria is more pronounced in the dark (particularly in the first 5 s of darkness).This sign is reportedly absent in 12% of Horner’s syndrome Classic triad of ipsilateral ptosis, pupillary miosis, and facial anhydrosis (absence of sweating), but rarely all signs present.Affected pupil becomes smaller over time.The fellow pupil may become involved later Pupil may be oval-shaped or shows segmental constriction. ![]() ![]()
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