Again, drugs are a common cause. Miotic drops are still encountered in the treatment of glaucoma and the constricted pupils of the morphine addict are well known if not so commonly seen. When a constricted pupil on one side is observed it is important to note the position of the eyelids. A slight degree of associated ptosis indicates the possibility of Horner's syndrome. The total syndrome comprises miosis, narrowing of the palpebral fissure because of paralysis of the smooth muscle in the eyelids (Muller's muscle), loss of sweating over the affected side of the forehead, a slight reduction of the intraocular pressure and enophthalmus (sunken globe). Horner's syndrome can be caused by a wide diversity of lesions anywhere along the sympathetic pathway. While a Pancoast's apical lung tumour is classically associated with Horner's syndrome, it is quite often noted in the elderly as an isolated finding and investigation fails to reveal a cause. The Argyll Robertson (AR) pupil is a rare but famous example of the miosed pupil, which responds to accommodation but not to direct light. This type of pupil reaction was originally described as being closely associated with syphilis of the central nervous system. Visual acuity is normal in such patients.
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