BrightMEM White Paper

A sample of content in this file:

BY JOSHUA HOU, MD
Background
PERSISTENT CORNEAL EPITHELIAL DEFECT
A persistent corneal epithelial defect (PCED) occurs when there is a failure of reepithelialization after a corneal
injury. According to recent estimates, there are approximately 97,000 cases of PCED a year in the United
States (7). Though there is no consensus definition or specific time frame for when delayed healing is
considered pathologic (5,6), any prolonged healing time for corneal epithelial defects increases the risk of
stromal melting, vision-reducing haze or scarring, and infection. Damage to the epithelial basement
membrane, the substrate that supports healthy epithelial cells, can lead to recurrent corneal erosions (8).
Therefore, healing any corneal epithelial defect as quickly as possible is essential to prevent long-term
complications and reduced vision.
Normal corneal epithelial healing is driven by the orchestrated efforts of multiple biologic pathways,
including cell proliferation and migration (9), cell-to-cell signaling, and extracellular
matrix remodeling and the interplay of numerous growth factors and cytokines (1,3).
Delayed corneal epithelial wound healing may be caused by different mechanisms, such as active
microbial infection, decreased corneal innervation (neurotrophic cornea), underlying limbal stem cell
deficiency (LSCD), surgical/mechanical/thermal trauma, and chronic expo-sure with resultant tear
evaporation and desiccation (1).
The corneal epithelium has many essential roles, including serving as a barrier to external trauma, germs,
toxins, and environmental threats and providing a smooth refractive surface to facilitate vision. Like all
epithelial layers in the body, there is constant turnover of epithelium,which is dependent upon proliferative
cells in the limbus and basal layers of the epithelium. These cells mature and differentiate, regenerating the
normal corneal epithelium throughout life (1-3). When the protective epithelial layer is disrupted, the eye
becomes susceptible to infection, degradation of underlying corneal tissue (stromal ulceration), perforation,
scarring, and significant vision loss (4-6). Persistent corneal epithelial defects (PCEDs) and limbal stem cell
deficiency (LSCD) are two challenging diseases where there is pathologic healing of the corneal epithelium.
While there are medical and surgical therapies to promote healing of damaged corneal epithelium in these
cases, therapies that provide long- term resolution of these diseases remain limited.