FIGURE 29.4 Physiologic anisocoria Relative difference in pupil size is the same in bright illumination (A) and dim illumination (B) TABLE 29.1 DIFFERENTIAL DIAGNOSIS OF UNEQUAL PUPILS a Physiologic anisocoria Pharmacologic (miotics or mydriatics) Local factors Miosis: iritis, surgical trauma Mydriasis: trauma Abnormal pupil shape from scar formation following prior iritis or trauma Neurologic causes Miosis: Horner syndrome Mydriasis: third cranial nerve palsy, Adie pupil Congenital abnormalities Iris coloboma Anterior chamber dysgenesis syndromes (e.g., Axenfeld–Rieger) a Not listed in order of frequency TABLE 29.2 COMMON CAUSES OF UNEQUAL PUPILS a Physiologic anisocoria Miosis Iritis secondary to trauma, juvenile rheumatoid arthritis, or idiopathic Migraines Abnormal pupil shape from scar formation following prior iritis or trauma Horner syndrome (Table 29.4 ) Mydriasis Trauma Third cranial nerve palsy Adie pupil Congenital abnormalities Iris coloboma a Not listed in order of frequency MIOSIS Local Factors An irritated or inflamed iris sphincter muscle will result in miosis Iritis, secondary to trauma or other factors, is a common cause (see Chapter 27 Eye: Red Eye ) The eye is usually injected, and there are symptoms of eye pain, photophobia, tearing, with or without decreased vision Injection may surround the cornea for 360 degrees, creating a ring of erythema (“ciliary blush”) More diffuse injection may also occur ( Fig 27.5 ) Traumatic iritis is often not apparent for 12 to 72 hours after eye trauma Children with juvenile idiopathic arthritis may not have these classic symptoms associated with their iritis; in fact, they may have no symptoms at all and may have delayed diagnoses Iritis from any cause, especially when longstanding (as is often seen in juvenile idiopathic arthritis) can result in scar tissues between the pupil edge and the lens just behind the pupil (posterior synechia), which prevent pupillary dilation or cause asymmetric irregular dilation of one or both pupils The diagnosis of iritis is confirmed by slit-lamp biomicroscopy This technique is described in Chapter 114 Ocular Trauma Ophthalmology consultation is important for evaluation and treatment TABLE 29.3 LIFE-THREATENING CAUSES OF UNEQUAL PUPILS a Miosis Intracranial mass lesion or vascular insult Spinal cord tumor or compression Intrathoracic tumor Aneurysm Cavernous sinus inflammation, thrombosis, or tumor Mydriasis Increased intracranial pressure Intracranial mass lesion Aneurysm Cavernous sinus inflammation, thrombosis, or tumor Orbital tumor a Not listed in order of frequency FIGURE 29.5 Congenital Horner syndrome The left iris is lighter in color than the right, the left pupil is miotic and there is a mild ptosis Other local factors include surgical irritation of the iris and pharmacologically induced unilateral miosis Mechanical contact with the iris during any intraocular surgical procedure may result in transient postoperative unilateral miosis Parasympathomimetic or sympatholytic systemic medications and topical drops can also result in transient miosis It is helpful to remember that most topical ophthalmic miotics are supplied in bottles that have green caps Neurologic Factors Congenital Horner syndrome may result from brachial plexus injury and is often associated with ipsilateral iris hypopigmentation (Fig 29.5 ) This sign is not as helpful in the first few months of life when both eyes are normally relatively hypopigmented More than 50% of children with congenital Horner syndrome have a history of difficult extraction at delivery Congenital varicella infection may also be a cause If the presence of Horner syndrome is questioned, one drop of topical 4% cocaine can be instilled into both eyes This testing is best performed by ophthalmology or neurology consultants Because cocaine prevents reuptake of norepinephrine at the terminal myoneural junction of the sphincter muscle, pupillary dilation will occur normally Failure of the miotic pupil to dilate is diagnostic of Horner syndrome Knowledge of the sympathetic system anatomy can be exploited through the use of other topically applied diagnostic agents (e.g.,