The corneal epithelium is a rapidly regenerating, stratified squamous epithelium. Homeostasis of corneal epithelial cells is an important prerequisite, not only for the integrity of the ocular surface, but also for the visual function. The maintenance of a healthy corneal epithelium under both normal and wound-healing conditions is achieved by a population of stem cells located in the basal layer of limbal epithelium. The Limbus represents the transition zone between the peripheral cornea and the bulbar conjunctiva. The stem cells from the limbus generate the transient amplifying cells that migrate, proliferate, and differentiate to replace lost or damaged corneal epithelial cells. In patients with aniridia, there is a primary dysfunction of these limbal stem cells (see Figure 6.1). The cornea is affected clinically in 90 percent of the patients with aniridia. In most cases, the cornea in aniridic patients appears normal and transparent during infancy and childhood. However, during the early teens, the cornea begins to show changes. The early changes are marked by the in-growth of opaque epithelium from the limbal region into the peripheral cornea, which represents conjunctival epithelial cells, goblet cells, and blood vessels in the corneal epithelium. These changes gradually progress toward the central cornea and may cause corneal epithelial erosions and epithelial abnormalities that eventually culminate in opacification of the corneal stroma, which leads to vision loss. With the gradual loss of limbal stem cells, the entire cornea becomes covered with conjunctival cells. Eventually, many patients develop total limbal stem cell deficiency. These abnormalities usually become more pronounced with aging. The corneal abnormalities seen in aniridia are collectively termed “aniridic keratopathy”. Significant corneal opacification may occasionally be the initial manifestation of aniridia. Abnormal tear film stability and meibomian gland dysfunction are also observed in patients with aniridia. This can lead to dry eyes, aggravating corneal erosion and ulceration observed in aniridic patients. Sometimes, aniridia is associated with “Peter’s anomaly,” in which central corneal opacity is present at birth along with defects in the corneal endothelium and Descemet’s membrane.
Differentiation of human embryonic stem cells derived mesenchymal stem cells into corneal epithelial cells after being seeded on decellularized SMILE-derived lenticules