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The Problem
“One of my child’s pupils is larger than the other.”
Common Causes
Physiological anisocoria
Horner syndrome
Other Causes
Third nerve palsy
Congenital iris anomalies
Physiological anisocoria
Mild asymmetry
Variable (pupils sometimes equal)
Horner syndrome
Pupils always unequal
Worse in dim light
Ptosis on side of smaller pupil
Possible decreased sweating of face on affected side
Unequal pupil color in congenital or early acquired cases
Associated with some systemic disorders
Thoracic or cervical surgery
Birth trauma with cervical injury
History of direct ocular injury
History of juvenile idiopathic arthritis
Ocular pain, redness
Exposure to topical medications or plants that affect pupil
Third nerve palsy
Strabismus, ptosis
Systemic diseases associated with third nerve palsy
Physiological anisocoria
Difference between pupils less than 1.0 mm
Variable, sometimes equal
Greater in dim light
Horner syndrome
Asymmetry greater in dim light
Mild ptosis on affected side
Possible unequal sweating on affected side
Possible difference in iris pigment (heterochromia)
Affected pupil may be smaller or larger than normal pupil
Other signs of ocular trauma
Pupil nonreactive, possibly irregular
Possible cataract

Mild (<0.5 mm) anisocoria in young children is usually normal, particularly if it is variable. Anisocoria associated with other disorders, particularly Horner syndrome and third nerve palsy, is not an isolated finding. If a patient has ptosis along with anisocoria, referral to a pediatric ophthalmologist is indicated for evaluation of possible Horner syndrome or third nerve palsy. If the pupil does not react at all, referral is also indicated.


What Shouldn’t Be Missed


Horner syndrome, particularly in older children, may result from serious diseases such as neuroblastoma. These patients require evaluation to look for these problems. Children with iritis secondary to juvenile idiopathic arthritis (JIA) may have no symptoms of ocular discomfort despite severe inflammation. In some of these patients, abnormal pupils due to scarring of the iris may be the first abnormality noted.


  • 1. Physiological anisocoria. Mildly asymmetric pupils may occur in otherwise normal infants. This may be familial. The anisocoria is more noticeable in dim light. The hallmark of physiological anisocoria is variability, with the pupils sometimes appearing equal. Physiological anisocoria does not cause any problems with development of vision.
  • 2. Horner syndrome. Horner syndrome occurs due to interruption of the oculosympathetic chain that begins in the hypothalamus, travels through the spinal cord to the thorax, and ascends along the internal carotid artery to the orbit. Lesions anywhere along this pathway may cause Horner syndrome. The syndrome is characterized by anisocoria (pupil smaller on the affected side), mild ptosis, and anhidrosis (decreased sweating on the affected side of the face) (Figure 18–1). It typically does not cause vision problems. It is important because of its association with other systemic conditions.
  • 3. Iritis. Most patients with iritis (intraocular inflammation) have marked eye discomfort and seek medical attention because of this complaint. For unknown reasons, children with iritis associated with JIA usually do not experience significant eye pain. Because of this, even severe inflammation may go unnoticed until substantial eye damage is present. Children with JIA sometimes present with nonreactive pupils due to scarring of the iris to the lens capsule (Figure 18–2).
  • 4. Pharmacological. Several eye drops or ...

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