Causes and Types of Abnormal Pupils

Argyll-Robertson Pupils Argyll-Robertson pupils are usually bilateral and result from tertiary syphilis of the nervous system, diabetes, or the late signs of bilateral tonic pupils (see the section on "Adie's Syndrome"). The pupils are small, irregular, and unequal. They do not react to light, they do react to near vision, they respond poorly to mydriatics, and they do not dilate in the dark. However, they can be made to constrict even more by the use of mi-otics. The poor light response and good near response may be relative; that is, the light response need not be absent, but is much less evident than the near response. Visual acuity is not impaired.

Horner's Syndrome Horner's syndrome, or oculosympathetic palsy (unilateral), presents with abnormalities of the eyelids as described in the section on "Ptosis." The pupil is small and round with good response to light and near. The difference between normal and abnormal pupil size in the dark is even greater; that is, the pupil on the side of the lesion dilates later and less. A lesion of the sympathetic fibers can be in the brain stem, cervical cord, apex of the lung, carotid sheath, or orbit.

Additional signs are apparent enophthalmos and a warm, dry, nonsweat-ing, ipsilateral face. A number of pharmacological agents can be used to aid the diagnosis and localize the lesion as central, preganglionic, or postgan-glionic.

Horner's syndrome, with pain in the eye and ipsilateral face and forehead, has been reported in dissection of the carotid artery and with cluster headaches with a normal carotid artery.

Oculomotor Nerve Lesion (Unilateral) Other features of the unilateral oculomotor nerve lesion are as described above. The pupil is mid-dilated. There is no response to light or near, and the difference in pupil size is greater in the light (in contrast with Horner's syndrome). Mydriatics and miotics are both effective. Diabetic oculomotor nerve palsies usually have normal pupils, and lesions can be painful.

Adie's Syndrome Adie's syndrome, or tonic pupil (which may be unilateral or asymmetrically bilateral), is also known as "the big, slow pupil." The condition presents as an enlarged pupil that either does not react to light or eventually constricts after being exposed to very bright light for 15-20 min. It eventually constricts for near after a similarly long effort. Redilatation is just as protracted. The difference in the pupil sizes is best seen in the light.

The pupils respond to mydriatics and miotics and demonstrate denervation supersensitivity. This means that the tonic pupil will constrict from 2.5% solution of Mecholyl or 0.125% pilocarpine. Normal pupils do not respond to these weak solutions.

Accommodation is just as slow as the light response and may be the presenting complaint. When the deep tendon reflexes are diminished or absent, the syndrome is called Holmes-Adie. The cause is unknown.

Benign Anisocoria Usually a young adult with benign anisocoria reports a difference in pupil size. The longer it has been present, the less likely it is to be important. Ask for some old photographs of the patient, and examine them for pupil inequalities. The response to light and near in both eyes is normal, the difference in pupil size is no greater in dimness or light, mydriat-ics and miotics have a normal response, and there is no diagnosis.

The Factitious Big Pupil Sometimes proprietary eyedrops have impurities in them with atropine-like properties. Patients using ointments with atropine-like properties may inadvertently introduce them into the eye.

There is occasionally a deliberate atropine abuser. He or she is usually working or studying in a hospital and has some access to medications and is under pressure or stress of some kind. The patient presents with the biggest pupil you have ever seen. There is not a flicker of response to light or near. The difference is greatest in bright light, and neither mydriatics nor miotics change the pupil.

Keep the patient talking (about anything), get the whole story, change the environment (if a medical student or nurse, keep him off the wards for the next 3 days if possible), and reexamine the eye daily for 3 consecutive days. If this big pupil is caused by medication, each day its response to light and near will be a little better and your chances of getting the full history improve. Pilocarpine will not constrict an atropinized pupil; it will, however, constrict an Adie's pupil.

Midbrain Lesions With midbrain lesions the pupils are large, particularly if the lesion involves the parasympathetic fibers of the third nerve. If the midbrain is totally interrupted, including the sympathetic fibers, the pupils are big, but less so.

Carotid Artery Occlusion (Unilateral) An enlarged pupil ipsilateral to the occlusion has been reported in atheroma and Takayasu's disease. The pupil reacts poorly to light (direct and indirect) and near. The explanation is probably ischemic atrophy of the iris, rather than nerve disease.

Pontine Miosis (Bilateral) The classic sign of pontine infarction or hemorrhage is small (1- to 1.5-mm) pupils. They will constrict to light if a bright enough stimulus is used and if examined through a magnifying glass.

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