Abnormalities of Pupil and Iris

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Chapter 614 Abnormalities of Pupil and Iris

Aniridia

The term aniridia is a misnomer because iris tissue is usually present, although it is hypoplastic (Fig. 614-1). Two thirds of the cases are dominantly transmitted with a high degree of penetrance. The other 30% of cases are sporadic and are considered to be new mutations. The condition is bilateral in 98% of all patients, regardless of the means of transmission, and is found in approximately 1/50,000 persons.

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Figure 614-1 Aniridia with minimal iris tissue.

(From Nelson LB, Spaeth GL, Nowinski TS, et al: Aniridia: a review, Surv Ophthalmol 28:621–642, 1984.)

Aniridia is a panocular disorder and should not be thought of as an isolated iris defect. Macular and optic nerve hypoplasias are commonly present and lead to decreased vision and sensory nystagmus. The visual acuity is measured as 20/200 in most patients, although the vision occasionally is better. Other ocular deformities are common and can involve the lens and cornea. The cornea may be small, and a cellular infiltrate (pannus) occasionally develops in the superficial layers of the peripheral cornea. Clinically, this appears as a gray opacification. The pannus results from a stem cell deficiency and therefore must be treated with keratolimbal stem cell transplantation rather than cornea transplantation. Lens abnormalities include cataract formation and partial or total lens dislocation. Glaucoma develops in as many as 75% of patients with aniridia.

Aniridia is caused by a defect in the PAX6 gene on chromosome 11p13. The PAX6 gene is the master control gene for eye morphogenesis. Aniridia can be sporadic or familial. The familial form is autosomal dominant with complete penetrance but variable expressivity. Sporadic aniridia is associated with Wilms tumor in as many as 30% of cases (Chapter 493.1). The combination of aniridia and Wilms tumor represents a contiguous gene syndrome in which the adjacent PAX6 and Wilms tumor (WT1) genes are both deleted. Some deletions create the WAGR complex of Wilms tumor, aniridia, genitourinary malformations, and mental retardation. All children with sporadic aniridia should undergo chromosomal deletional analysis to exclude the possibility of Wilms tumor formation. Children who test positive for the deletion should undergo repeated abdominal ultrasonographic and clinical examinations. Wilms tumor has also been reported in patients with familial aniridia. Therefore, these patients should also undergo chromosomal analysis.

Horner Syndrome

The principal signs of oculosympathetic paresis (Horner syndrome) are homolateral miosis, mild ptosis, and apparent enophthalmos with slight elevation of the lower lid. Patients may also have decreased facial sweating, increased amplitude of accommodation, and transient decrease in intraocular pressure. If paralysis of the ocular sympathetic fibers occurs before the age of 2 yr, iris heterochromia with hypopigmentation of the iris can occur on the affected side but can take time to develop.

Oculosympathetic paralysis may be caused by a lesion in the midbrain, brainstem, upper spinal cord, neck, middle fossa, or orbit. Congenital oculosympathetic paresis, often as part of Klumpke brachial palsy, is common, although the ocular signs, particularly the anisocoria, can pass undetected for years. Horner syndrome is also seen in some children after thoracic surgery, such as for congenital heart disease. Congenital Horner syndrome can occur in association with vertebral anomalies and with enterogenous cysts. In some infants and children, Horner syndrome is the presenting sign of tumor in the mediastinal or cervical region, particularly neuroblastoma.

The diagnosis of Horner syndrome can be confirmed with the use of topical cocaine or apraclonidine drops. A normal pupil dilates within 20-45 min after instillation of 1 or 2 drops of 4% cocaine, whereas the miotic pupil of an oculosympathetic paresis dilates poorly, if at all, with cocaine. Apraclonidine causes reversal of the anisocoria with dilation of the affected (smaller) pupil and no effect on the normal pupil. It should be used in caution in young children because it can cause excessive sedation owing to its CNS side effects. Pharmacologic testing might not be needed in the presence of typical clinical findings.

Horner’s syndrome in children can result from trauma, surgery, or the presence of neuroblastoma affecting the sympathetic chain in the chest. Evaluation of acquired Horner syndrome in a child without a history of trauma or surgery that could explain the anisocoria should include imaging studies of the brain, neck, and chest. Examining old photographs and old records is sometimes helpful in establishing the age at onset of Horner syndrome.

Dilated Fixed Pupil

Differential diagnosis of a dilated unreactive pupil includes internal ophthalmoplegia caused by a central or peripheral lesion, Hutchinson pupil of transtentorial herniation, tonic pupil, pharmacologic blockade, and iridoplegia secondary to ocular trauma.

The most common cause of a dilated unreactive pupil is purposeful or accidental instillation of a cycloplegic agent, particularly atropine and related substances. Central nervous system lesions, such as a pinealoma, can cause internal ophthalmoplegia in children. Because the external surface of the oculomotor nerve carries the fibers responsible for pupillary constriction, compression of the nerve along its intracranial course may be associated with internal ophthalmoplegia, even before the development of ptosis or an ocular motility deficit. Although ophthalmoplegic migraine is a common cause of a 3rd nerve palsy with pupillary involvement in children, an intracranial aneurysm must also be considered in the differential diagnosis. The blown pupil of transtentorial herniation, occurring with increasing intracranial pressure, is generally unilateral, and patients usually are obviously ill. The pilocarpine test can help differentiate neurologic iridoplegia from pharmacologic blockade. In the case of neurologic iridoplegia, the dilated pupil constricts within minutes after instillation of 1 or 2 drops of 0.5-1% pilocarpine; if the pupil has been dilated with atropine, pilocarpine has no effect. Because pilocarpine is a long-acting drug, this test is not to be used in acute situations in which pupillary signs must be carefully monitored. Because of the consensual pupil response to light, even complete uniocular blindness does not cause a unilaterally dilated pupil.

Leukocoria

Leukocoria includes any white pupillary reflex, also called cat eye reflex. Primary diagnostic considerations in any child with leukocoria are cataract, persistent hyperplastic primary vitreous, cicatricial retinopathy of prematurity, retinal detachment and retinoschisis, larval granulomatosis, and retinoblastoma (Fig. 614-2). Also to be considered are endophthalmitis, organized vitreous hemorrhage, leukemic ophthalmopathy, exudative retinopathy (as in Coats disease), and less-common conditions such as medulloepithelioma, massive retinal gliosis, the retinal pseudotumor of Norrie disease, the pseudoglioma of the Bloch-Sulzberger syndrome, retinal dysplasia, and the retinal lesions of the phakomatoses. A white reflex might also be seen with fundus coloboma, large atrophic chorioretinal scars, and ectopic medullation of retinal nerve fibers. Leukocoria is an indication for prompt and thorough evaluation.

The diagnosis can often be made by direct examination of the eye by ophthalmoscopy and biomicroscopy. Ultrasonographic and radiologic examinations are often helpful. In some cases, the final diagnosis rests with a pathologist.