Pupils normally constrict when exposed to direct light, but if the pupil is constricted and does not change with exposure or removal of light, it may indicate a range of conditions, such as a reaction to medication, Horner's syndrome and could even point to narcotic abuse, according to WebMD. If pupil constriction seems irregular, seek medical attention immediately.
The above ailments are associated with other symptoms like nausea, fatigue, dizziness and drooping eyelids. Although resources like WebMD can assist in finding common causes for a constricted pupil, there may be other reasons for the constriction. It is advised to refer to a physician for further medical advice and let them decide how to treat the condition.