The cornea is the clear, dome-shaped outer layer at the very front of the eye. It acts as a transparent window, allowing light to enter the eye and reach the structures within. This protective covering plays a significant role in vision, constantly exposed to the external environment. Without a healthy, clear cornea, light cannot properly reach the retina, which can impact vision.
The Structure and Function of the Cornea
The cornea performs two primary functions. It acts as the eye’s outermost lens, bending incoming light to focus it onto the retina. This refractive power contributes a large portion, approximately 65-75 percent, of the eye’s total focusing ability. A smooth, precise curvature of the cornea is therefore necessary for sharp, detailed vision.
Beyond its optical role, the cornea also serves as a strong barrier, shielding the inner parts of the eye from dust, germs, and injuries. This protective task is shared with the eyelids, tears, and the sclera. The cornea achieves clarity because it is avascular, meaning it does not contain blood vessels. This allows light to pass through unimpeded, unlike other tissues that rely on blood vessels for nourishment.
The cornea is composed of distinct layers, each contributing to its overall strength and function. The outermost layer, the epithelium, acts as a tough, protective outer layer, providing a smooth surface for the tear film. Beneath this lies the stroma, which is the main structural middle layer, making up the largest portion of the cornea’s thickness. The precise arrangement of collagen fibers within the stroma is responsible for the cornea’s transparency and strength.
Common Corneal Conditions
A corneal abrasion is a physical scratch on the cornea’s surface. These injuries can result from various occurrences, such as accidental pokes, dirt, or improper contact lens handling. Symptoms often include sudden eye pain, a sensation that something is stuck in the eye, excessive tearing, and increased sensitivity to light. While minor abrasions can heal relatively quickly, larger ones may require medical attention to prevent complications.
Keratitis describes inflammation or infection of the cornea. It can stem from bacteria, viruses, fungi, or parasites, often linked to poor contact lens hygiene. Symptoms include redness, eye pain, blurry vision, and sometimes discharge or pus from the eye. Untreated keratitis can lead to corneal ulcers and scarring, potentially causing vision loss.
Keratoconus is a degenerative disease where the cornea gradually thins and bulges outward into a cone shape. This progressive change in shape distorts how light enters the eye, leading to blurred and distorted vision. Individuals with keratoconus often experience increasing nearsightedness and astigmatism, making it difficult to achieve clear vision with standard eyeglasses. The exact cause is not always clear, but genetic factors and eye rubbing are believed to play a role.
Treatments for Corneal Disorders
Treatments for corneal disorders vary widely depending on the specific condition and its severity. For infections and inflammation, medicated eye drops are prescribed. These drops may contain antibiotics, antiviral, or anti-inflammatory medications to reduce symptoms and promote healing. Artificial tears can also provide relief for conditions causing dryness or irritation.
For vision problems caused by corneal shape irregularities, such as early-stage keratoconus, corrective lenses are used. Standard eyeglasses can help in milder cases, while specialty contact lenses, such as rigid gas permeable lenses, are designed to create a smooth refractive surface over the irregular cornea, improving vision. These specialized lenses can enhance visual acuity for more advanced conditions.
When corneal damage is extensive or vision is significantly impaired, corneal transplant surgery, also known as keratoplasty, may be recommended. This procedure involves replacing the damaged or diseased cornea with healthy corneal tissue obtained from a deceased donor. During the surgery, the ophthalmologist carefully removes the affected portion of the patient’s cornea and sutures the donor tissue into place. This intervention can restore vision and alleviate symptoms in severe corneal diseases that have not responded to other treatments.