![]() The ocular motor systems control eye lid closure, the amount of light that enters the eye, the refractive properties of the eye, and eye movements. We use our eyes to monitor our external environment and depend on our ocular motor systems to protect and guide our eyes. They involve the action of few muscles and of well defined neural circuits. The optometrist who finds one of these conditions will either take no action, having explained the findings to the patient, or refer the patient to the ophthalmologist or neurologist if tests are needed.The simplicity of the motor systems involved in controlling eye musculature make them ideal for illustrating the mechanisms and principals you have been studying in the preceding material on motor systems. How is Abnormalities of the Pupil managed? This condition is usually seen at a late stage of the sexually-transmitted infection syphilis and shows that the disease has affected the nervous system. In Argyll Robertson pupil, both pupils are small and there is no reaction to light, but constriction for looking at near objects still happens. It can occur in babies who are injured during birth, and in people with disease of the blood vessels, cancer or following some types of operation. In another condition, there is a small pupil on one side, a drooping of the upper lid, and no sweating on the same side of the face. 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.Affected pupil larger than normal, with decreased response to light but preserved or enhanced near response.Degree of anisocoria remains relatively constant in light and dark conditions.Thought to result from a lesion in the midbrain that disables the pathway for the pupillary light reflex but does not affect the more ventral pathway mediating the near reaction.Usually benign or occurs after surgery, but could also indicate a carotid dissection or neoplasia.Caused by interruption of the oculosympathetic innervation at any point along the neural pathway from the hypothalamus to the orbit. ![]()
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