Encyclopedia - Hyperopia (Farsightedness)

How does the eye see?
What causes hyperopia?
How is hyperopia corrected?

Hyperopia is the ability of the eye to clearly see objects at a distance but not up close. For instance, a person who is farsighted can see to drive, but needs corrective lenses for reading.

How does the eye see?

The eye functions much like a camera with two lenses. The first lens is the cornea, a clear membrane that covers the front of the eye. The second lens is the eye's natural crystalline lens, which is located behind the pupil. The cornea is responsible for about 70 percent of the eye's focusing power, while the natural lens "fine-tunes" the image before it is focused on the retina at the back of the eye. The retina works like the film in a camera, receiving light images and sending them through the optic nerve to the brain. (See Anatomy of the Eye.) If both lenses are working properly, the image is focused precisely on the surface of the retina.

What causes hyperopia?

Hyperopia is an inherited condition that occurs when the cornea is too flat or the distance from the cornea to the retina is too short. When this happens, the light rays coming from an object strike the retina before coming to sharp focus, or the image is theoretically focused at an imaginary point behind the retina. The result is a blurred image when trying to focus on something that is up close, but distance vision remains sharp.

Children who are farsighted can sometimes compensate without corrective lenses because of the strength and agility of their natural lenses. With a high degree of hyperopia, however, they may exhibit nonvisual symptoms such as headaches and lack of interest in reading. As the eye gets older, it loses some of its ability to accommodate (focus), and eventually, most farsighted individuals need corrective lenses.

How is hyperopia corrected?

The usual treatment for hyperopia is prescription eyeglasses with convex lenses that curve outward, or contact lenses that counteract the distortion created by corneas that are too flat in shape. A convex lens moves the image of a distant object forward onto the retina, thereby bringing it into proper focus.

Refractive eye surgery, which steepens the cornea, has recently become an option for the correction of farsightedness. The most popular of those procedures is Laser In-Situ Keratomileusis (LASIK), which uses an Excimer laser to reshape the cornea. Other procedures that show promise for the surgical correction of hyperopia include Implantable Contact Lenses (ICLs) that fit between the iris and the natural lens of the eye, and Clear Lens Extraction (CLE) during which the eye's natural lens is replaced by a plastic intraocular prescription lens. Another procedure that shows promise for the treatment of hyperopia is Laser Thermal Keratoplasty (LTK), which uses a Holmium laser to shrink the peripheral area of the cornea in order to steepen the shape. Refractive eye surgery is usually not recommended for people under 18 years of age.