Constricted pupil may indicate physiologic anisocoria

August 1, 2004

Iowa City, IA-The constricted pupil is both easy and hard to diagnose. As with the dilated pupil, there are easy-to-diagnose conditions in the patient with a small pupil-such as physiologic anisocoria, Horner's syndrome, and iris abnormalities-and these occur commonly. Pharmacologic miosis, Adie's pupil, and aberrant regeneration of the third nerve, however, are a bit harder to pinpoint, according to Andrew G. Lee, MD, who outlined his practical approach to diagnosing the constricted pupil.

Dr. Lee used the case of a constricted pupil in a 30-year-old man who had been involved in a motor vehicle accident to demonstrate what ophthalmologists should look for. The question, he pointed out, is: "Is the constricted pupil the problem and if so, is it a sign of a Horner's syndrome?"

Dr. Lee, professor of ophthalmology, neurology, and neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, enumerated the steps needed to establish a diagnosis. To determine if the small pupil is abnormal, the light reaction should be tested, he said; if it is normal in both eyes, then the amount of anisocoria should be measured in both the light and dark. If the amount of anisocoria is equal in light and dark and there is no other sign of Horner's syndrome (e.g., ptosis, "upside down" ptosis, dilation lag of the pupil), then physiologic anisocoria is likely.

If the light reaction in the larger pupil is abnormal, then that is the abnormal pupil. If, however, the light reaction is poor in the smaller pupil, then additional testing is warranted for causes of a miotic pupil. A thorough slit-lamp examination can then rule out any iris abnormality causing a small pupil (e.g., posterior synechiae). If the light reaction is abnormal, then the near reaction can be tested. If the near reaction is normal or greater than normal in a smaller pupil, then light-near dissociation of the pupil is present (e.g., Adie's tonic pupil or aberrant

"Check the light reaction in the pupils, and if the enlarged pupil does not react, it is the problem. If the smaller pupil does not react-and this point is underappreciated-then the small pupil is the problem. If the light reaction test does not provide information, then the anisocoria must be checked in the light and dark. The bottom line is that the dysfunctional pupil is the one that does not react to light and sometimes that is the miotic pupil," he said.

The easy diagnoses When faced with diagnosing such a patient, most have physiologic anisocoria. Characteristics include a normal reactive pupil, no ptosis, no dilation lag, and equal anisocoria in light and dark. Iris abnormalities (posterior synechiae), the other common problem, are usually visible during the slit-lamp examination.

Horner's syndrome, the most serious of the diagnoses, is characterized by a normal light reaction and greater anisocoria in the dark, because it is a dilation problem, Dr. Lee explained. Other symptoms, such as ipsilateral miosis of the pupil, 1 to 2 mm of ptosis of the upper lid, upside-down ptosis of the lower lid, and dilation lag (anisocoria tested at 5 seconds will be greater than at 15 seconds) also occur.