Iris and Pupils

Iris and Pupils

Alex V. Levin

Thomas W. Wilson

J. Raymond Buncic

David Rootman

The iris is formed during ocular development by an extension of the optic vesicle (neuroectoderm) forward as the posterior pigmented and nonpigmented iris epithelium, and an influx of neural crest cells forming the iris stroma. The iris sphincter and dilator muscles differentiate from the epithelial layers. Mesoderm contributes the endothelial lining of the vessels.

Abnormalities of embryogenesis can lead to iris anomalies including coloboma, persistent pupillary membranes, aniridia, and Axenfeld-Reiger syndrome. Iris findings can often give clues to underlying systemic diseases including Down syndrome (Brushfield spots), neurofibromatosis type 1 (Lisch nodules), Williams syndrome (stellate iris), and Hirschsprung syndrome (sector iris heterochromia). Abnormalities of the iris are also associated with other ocular abnormalities in diseases such as aniridia, albinism, and coloboma. Iris abnormalities can be the first clues of an underlying systemic disease or genetic disorder.

Figure 6.1 Aniridia

Aniridia is an autosomal dominant abnormality of ocular development caused by a defect in the PAX6 gene located at chromosome 11p13. The association of Wilms tumor, sporadic aniridia, genitourinary abnormalities, and mental retardation is termed WAGR syndrome and is due to contiguous gene deletion in this region. Patients with aniridia will often present with nystagmus, photophobia, and decreased vision. Clinical findings include complete or partial absence of the iris, keratitis, cataract, macular hypo- plasia, and optic nerve hypoplasia. Glaucoma is present in ap- proximately one third of patients with aniridia and cataracts in approximately 50%.

Figure 6.2 Aniridia—Glaucoma

Glaucoma is a common association with aniridia. One fourth to one third of patients with aniridia will develop angle closure glaucoma in the first decade of life. The possible mechanisms include aplasia of the Schlemm canal, goniodysgenesis, or migration of the rudimentary iris stump forward, as shown here, resulting in obstruction of the trabecular meshwork. Medical treatment is often not successful and glaucoma surgery is required to control the intraocular pressure.

Figure 6.3 Aniridia—Macular Hypoplasia

Aniridia is often associated with nystagmus and visual loss. The most common cause of vision loss in a patient with otherwise clear media is macular and optic nerve hypoplasia. This photograph shows abnormal macula throughout the deeply depressed light reflex centrally. The retinal blood vessels also do not respect the foveal avascular zone. The optic nerve in this photograph also appears hypoplastic.

Figure 6.4 Gillespie Syndrome

Gillespie syndrome is the association of aniridia and cerebellar ataxia and mental retardation. Aniridia associated with Gillespie syndrome is not caused by mutations of the PAX6 gene, and is therefore not associated with Wilms syndrome. The disorder is autosomal recessive. Note the typical scalloped pupil margin and more robust iris stump as compared to classic aniridia (Fig. 6.1).

Figure 6.5 Congenital Iris-Lens- Pupillary Membrane Syndrome

This photograph demonstrates secondary congenital miosis from a traction band extending across the borders of the pupil. White fibrous material seen centrally represents a remnant of the tunica vasculosa lentis. This form of persistent fetal vasculature (Chapter 7: Lens, Fig. 7.2) is characterized by corectopia and a high risk for glaucoma. The membrane may also extend behind the iris. Surgical pupilloplasty would be necessary in cases where the visual axis is significantly obstructed.

Figure 6.6 Physiologic Anisocoria

To be considered physiologic, the relative difference in the pupil sizes should be the same in light and dark conditions. There should be full extraocular movements and no evidence of ptosis. Old photographs are often helpful to determine the chronicity of the anisocoria. Further workup including neuroimaging, cocaine testing, and evaluation for neuroblastoma should be considered with any other neurologic or associated ocular findings.

Figure 6.7 Iris Pupillary Cysts

Congenital cysts of the iris pigment epithelium are commonly detected on red reflex testing by the pediatrician. This photograph shows a group of cysts that are not obscuring the visual axis. Glaucoma is not typically associated with these cysts. The cysts tend to be multiple and are not large enough to occlude the visual axis. The cysts may rupture or collapse over time. Chronic use of phospholine iodide can cause similar cysts and will resolve with discontinuation of the medication. Cysts that occlude the visual axis can be disrupted with neodymium YAG capsulotomy or anterior segment surgery.

Figure 6.8 Congenital Iris Ectropion Uvea

Congenital ectropion uvea is an abnormal migration of posterior pigment epithelial into the anterior iris surface. The patient will often present with concerns regarding anisocoria or iris pigmentation. Clinical examination shows an irregular pigmented mass on the anterior surface of the iris with distortion of the pupil and corectopia. Secondary glaucoma will commonly present, requiring surgical treatment. The disorder is almost always unilateral and nonheritable. Histology shows a residual contractile cellular lining attached to the leading edge of the ectropion and possibly covering the trabecular meshwork.

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Jul 29, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Iris and Pupils

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