The cornea is the eye's transparent tissue, which is the outmost protective layer. The cornea and the sclera help prevent germs, dirt and harmful particles. The cornea curvature helps the eye focus light. The cornea can also filter out some ultraviolet rays.
The cornea contains three main layers: epithelium, stroma, endothelium. The epithelium layer absorbs oxygen and nutrients, it also prevents harmful particles. The stroma layer contains water and proteins, which make the stroma elastic but solid. Behind the stroma is the endothelium layer, which can help expell excess water.
The common cornea diseases include: conjunctivitis (also known as pink eye), microbial infections (keratitis), ocular herpes, herpes zoster, corneal dystrophies.