The cornea is the clear, rounded outer layer of the eye. Despite its clear appearance, it actually consists of three layers (the epithelium, the stroma, and the endothelium), plus the two thinner layers that separate them (Bowman’s membrane and Descemet’s membrane). Because the cornea contains no blood vessels to supply it with nutrients, help wounds heal, and fight infection (unlike the most other tissues in the anatomy), it is nourished by tears and a fluid called aqueous humour to serve these functions.
One of its main functions is to protect the eye from things that could cause injury or damage, such as dirt, debris or germs.The epithelium is full of nerve endings, which helps you feel if there is something in your eye, even as light as an eyelash. The cornea also helps protect your eyes from the sun’s harmful UV rays.
The other important role the cornea plays is to focus most of the light that comes in to the eye(about 65-75%) on to the retina at the back of the eye. The retina then converts this light into signals that are sent, via the optic nerve, to the brain to be perceived as images –so if the light isn’t refracted properly by the cornea, the retina can’t make a clear picture.
That’s why any injury to, or misshaping of, the cornea can lead to vision problems and should be treated. If you have a disorder of the cornea, you could have symptoms such as eye pain, light sensitivity, reduced or blurry vision, redness or swelling in the eye, or headache, nausea and fatigue – depending on the source of the problem.
Some of the conditions that can result in problems with the cornea include allergies (from hay-fever, pet dander, or dust for example), dry eye (when the eye fails to produce sufficient tears), or keratitis (an inflammation of the cornea, often due to injury, wearing contacts for too long, or infection).
The cornea can also lose clarity and function from a set of conditions called dystrophies, the effects of which can vary from no symptoms at all, to pain without vision loss, to severe impairment of vision. Types of dystrophies include keratoconus (progressive thinning of the cornea), Fuch’s dystrophy (the deterioration of endothelium cells), lattice dystrophy (protein deposits on the stroma), and map-dot-fingerprint dystrophy (folds in the tissue of the epithelial membrane).
Treatments for corneal disorders or dystrophies will of course depend on the diagnosis made by an ophthalmologist. For advanced forms of corneal eye disease, surgery is the usual course of treatment. A type of laser surgery, known as phototherapeutic keratectomy (or PTK), is the choice for recurrent erosion of the cornea, as well as corneal dystrophies. Another type of surgery is anterior lamellar keratoplasty, used to treat keratoconus, severe scarring of the cornea, and dystrophies that affect the stroma layer; endothethial lamellar keratoplasty treats Fuch’s dystrophy, post-cataract edema, or corneal failure following operations for cataracts, glaucoma, or retinal detachment. Finally, full corneal transplants can be an option using either donor tissue or an artificial cornea called a keratoprosthesis.
This blog post is offered by Moorfields paediatric ophthalmologist Dubai.