How The Cornea Works?

Laser-assisted refractive surgery is becoming steadily more popular as a means of correcting the vision of the millions of Americans affected by nearsightedness or farsightedness. While there are different forms of the surgery, all of them do the same basic thing, improving the cornea’s ability to refract light by fixing imperfections of its shape.

Understanding the function of the cornea and how it impacts how well you see is an important part of understanding how laser-assisted refractive surgery can help improve your vision.

Your cornea is a transparent covering over the front part of the eye that’s over your iris, pupil and anterior chamber. The cornea serves multiple purposes, forming a protective barrier against germs and dirt, filtering out ultraviolet rays and helping to refract light, an important component of vision.

There are three main components of the cornea, the endothelium, the stroma and the epithelium. The endothelium is the innermost layer of the cornea and consists of a single layer of cells between your stroma and a clear fluid located in the front and rear chambers of your eye called the aqueous humor. Your endothelium acts as pump, helping to remove water that is absorbed into your stroma. If the endothelium doesn’t work properly, your stroma can become hazy, causing your vision to become fuzzy.

The stroma is your cornea’s largest layer and is directly beneath the epithelium. It’s mostly made up of proteins called collagen and water, but has a solid, although also elastic, form. The stroma accounts for 90 percent of the cornea’s size and the stroma’s collagen accounts for its light-bending refractive properties.

The epithelium is the outermost layer of your cornea and works to prevent foreign objects and UV rays from getting into your eye.

How your cornea affects your vision?

Your cornea works with your lens to refract light. This partnership between the cornea and lens makes up about 66 percent of the total optical power of your eye. The average human cornea has a refractive power of about 43 dioptres (a dioptre is a measurement of optical power, and is equivalent to the reciprocal of the focal length as measured in meters).

Although your cornea provides most of the focusing horsepower of the eye, its focus is static, however your lens can adjust to “tune” the eye’s focus, dependent, of course on the distance of the object you’re looking at from your eye.

A lot of the cornea’s ability to refract light is based on its shape. If the cornea is imperfectly shaped, it doesn’t refract light properly, resulting in conditions such as nearsightedness or farsightedness.

How laser eye surgery improves the cornea?

Traditional treatments for deformities of the cornea have included eyeglasses and contact lenses, which work to compensate for the corneal deformity by refracting light to the degree that the cornea should have. In the 20th century, a number of surgeries were developed to correct the shape of the cornea, thus making contacts and glasses uneccessary. The advent of laser surgery using an excimer laser revolutionized this field, increasing success rates and decreasing complications and recovery times.

The basic concept behind each form of laser-assisted refractive surgery is reshaping the cornea into the perfect shape to refract light. This is done by removing or lifting the epithelial layer of the cornea and using an excimer laser to resculpt the stroma. The excimer laser is a “cool” laser so it doesn’t burn the areas around the stroma or leave scarring. It’s very precise and accurate, abalating only the tissue that needs to be removed to reshape the eye to better refract light.

The earliest form of laser-assisted refractive surgery, PRK, required the removal of the epithelial layer. This causes some discomfort in the patient and also results in a longer recovery period as the patient must wait for the epithelium to grow back and stave off infection or irriation in the meantime. Later-developed surgeries, such as LASIK and LASEK, involve cutting a flap in the corneal tissue. Once the surgery is done, the flap is replaced and eventually re-fuses with the tissue beneath. This results in less discomfort and a quicker recovery time.

The use of laser-assisted refractive surgery to improve the performance of the cornea has been proven to be safe and effective. More than 90 percent of all patients using laser-assisted refractive surgery report improved vision, many achieving 20/20 or perfect vision. Continuing innovations and refinements of the technology, including wavefront technology, are increasing the accuracy and success of laser-assisted refractive surgery.

Tagged cornea, endothelium, epithelium, farsightedness, Laser-assisted refractive surgery, LASIK, nearsightedness, prk, stroma