Aniridia is the absence of the iris. This generally bilateral condition is trans-mitted as an autosomal dominant trait or occurs sporadically. Aniridia mayalso be traumatic and can result from penetrating injuries. However, periph-eral remnants of the iris are usually still present so that ciliary villi and zonule fibers will be visualized under slit-lamp examination (Fig. 8.2).
In sporadic aniridia, a Wilms’ tumor of the kidney should be excluded.
Vision is severely compromised as a result of the foveal hypoplasia. The dis-order is frequently associated with nystagmus, amblyopia, buphthalmos, and cataract.
Visual acuity will generally be reduced in the presence of
Another congenital anomaly results from incomplete fusion of the embry-onic optic cup, which normally occurs in about the sixth week of pregnancy.These anomalies are known as colobomas. They are directed medially and inferiorly and can involve the iris (Fig. 8.3), ciliary body, zonule fibers, choroid, and optic nerve (Fig. 8.4). Bridge colobomas exhibit remnants of the iris or choroid. Involvement of the choroid and optic nerve frequently leads to reduced visual acuity.
Surgical iris colobomas in cataract and glaucoma surgery are usuallyopened superiorly. In this manner, they are covered by the upper eyelid so the patient will not usually experience blinding glare.
Traumatic iris colobomas are caused by avulsion of the iris (iridolysis;Fig. 8.5).