Hyperopia

Definition

Hyperopia, also known as hypermetropia or far-sightedness, is the condition of the eye in which incoming rays of light reach the retina before they converge into a focused image.

Description

When light goes through the lens and cornea, its velocity decreases. The greater the curvature of the lens system, the greater the change in the direction of the light. When parallel light rays from an object go through the lens system, they are bent so they converge at a point some distance behind the lens. With perfect vision this point of convergence is on the retina. Hyperopia is the condition in which the point of focus of parallel light rays from an object is behind the retina. This condition exists when the combined curvature of the lens and cornea is insufficient (e.g., flatter than needed for the length of the eyeball).

There is a connection between the focusing of the lens of the eye (accommodation) and convergence of the eyes (the two eyes turning in to point at a close object). The best example is during reading. The lens accommodates to bring close-up material into focus and the eyes turn in to view the print and keep it single. Because of this connection between accommodation and convergence, the eyes may appear to turn in if the lens needs to accommodate to focus, even on distant objects. This can result in a condition known as accommodative esotropia. The eyes turn in and the cause is accommodation because of hyperopia.

Causes and symptoms

Most babies are born slightly hyperopic. This tends to decrease with age. In some eyes the cornea is too flat for the distance between the cornea and the retina. If the hyperopia is not too severe the lens may accommodate and focus the image onto the retina. This results in clear distance vision, also potential headaches or eyestrain. If the lens cannot accommodate for the full amount of the hyperopia, the distance image would be blurry.

If the eyes are focusing for distance and the patient shifts his or her gaze to a near object, the eyes need to accommodate further. This may result in nearby objects appearing blurry, or the patient may experience headaches while performing work on objects that are close to the eyes.

Symptoms can range widely depending on the severity of hyperopia. There may be no noticeable symptoms, distance vision may be clear but near vision blurry, or both distance and near vision may be blurry. Headaches and eyestrain may occur, particularly when performing near tasks. An eye turned in (esotropia) may be a result of hyperopia, particularly in children.

Diagnosis

To determine hyperopia, a complete eye exam should be performed by an ophthalmologist (M.D.) or optometrist (O.D.). The exam should begin by the physician or ophthalmic assistant taking a detailed medical history from the patient. Then the physician, or in some cases a highly trained ophthalmic assistant, will begin the ocular examination by measuring the visual acuity and performing a refraction.

During the exam the physician will also determine ocular motility and alignment, nearpoint of convergence, near fusional vergence amplitudes, relative accommodation measurements, accommodative amplitude, and facility of accommodation. Additional ocular health assessment and screenings should rule out other accommodative dysfunctional disorders such as Graves' disease.

Treatment

The usual treatment for hyperopia is corrective lenses (eyeglasses or contact lenses ). Plus-powered spherical or spherocylindrical lenses are prescribed. In some instances, physicians will choose pharmaceuticals to reduce a high accommodative convergence to accommodation.

In June 2000, the Food and Drug Administration (FDA) approved the first laser treatment for hyperopia. Laser thermal keratoplasty (LTK), performed by an M.D., takes three seconds per eye and involves no cutting or removal of corneal eye tissue. The holium:YAG laser uses a process for shrinking collagen and applies two concentric rings of eight simultaneous spots of laser energy to the periphery of the cornea. The laser heats the corneal collagen and steepens its shape, improving refractive (focusing) power.

LTK patients must be at least 40 years old; have stable vision for at least six months; fall in the low-to-moderate range of hyperopia (+0.75 diopters to +2.50 diopters); and have no more than 0.75 diopters of astigmatism. A complete medical history must be taken before the procedure is performed. Patients who fall into any of the following categories should not have LTK performed:

• pregnant or nursing women
• patients with clinically significant corneal dystrophy or scarring in the 6 mm or 7 mm central zone
• patients with a history of herpetic keratitis
• patients with an autoimmune disease, collagen vascular disease, clinically significant atopic syndrome, insulin dependent diabetes or an immune compromised status

Investigation of phakic intraocular lenses to treat hyperopia continues. As of early 2001, there were three separate FDA clinical trials in progress. The most promising is an implantable contact lens to treat hyperopia that is injected through a clear corneal incision.

In conjunction with these treatments, physicians may also want to address environmental factors to treat hyperopia, and advise patients to reduce glare and improve lighting and ergonomic conditions in their work stations.

Prognosis

Patients with low to moderate amounts of hyperopia have an excellent opportunity to receive fully corrected vision with eyeglasses, contact lenses or refractive surgery. Patients with very high hyperopia (+10.00D or more) may not achieve full correction.

Hyperopia increases the chances of chronic glaucoma, but vision loss from glaucoma is preventable.

Health care team roles

Nursing and allied health professionals perform an important role in the examination to determine hyperopia. They take a detailed patient history, insert eyedrops, and ready the physician's instruments. Skilled technicians also can perform the first level of refraction in the general eye exam. Depending on the technician's skill level, the physician may check these findings. Technology also allows technicians to perform parts of the exam previously only completed by the eye doctor, including corneal topography, retinal photography, and automated keratometry.

Ophthalmic assistants and nurses also assist in the screening of LTK patients. They prep the patients for surgery and may insert anesthetic eyedrops.

KEY TERMS

Accommodation— The ability of the eyes to focus clearly at various distances.

Cornea— The clear, dome-shaped outer covering of the front of the eye. It lies in front of the iris and pupil.

Iris— The colored ring just behind the cornea and in front of the lens that controls the amount of light sent to the retina.

Pupil— The black hole in the center of the iris. Light enters here on the way to the lens and retina.

Refraction— Method of determining the optical status of the eyes. Lenses are placed before the patient's eyes while reading from an eye chart. The result is the eyeglass prescription.

Retina— The inner, light-sensitive layer of the eye containing rods and cones; transforms the image it receives into electrical messages sent to the brain via the optic nerve.

Prevention

Hyperopia is usually present at birth, and there is no known way to prevent it.

Resources

BOOKS

Newell, Frank W. Ophthalmology: Principles and Concepts, 8th edition. St. Louis: Mosby, 1996.

ORGANIZATIONS

American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. ?http://www.eyenet.org?.

American Optometric Association. 2420 North Lindbergh Boulevard, St. Louis, MO 63141. (800) 365-2219. ?http://www.aoanet.org?.

OTHER

Edmiston, D. "Hyperopia." ?http://www.eyeinfo.com/hyperopia.html?.

"New technologies continue to expand options for treating keratoconus, myopia, hyperopia." Primary Care Optometry News ?http://www.slackinc.com/eye/pcon/200101/newtec.asp?.

"Optometric Clinical Practice Guideline Care of the Patient with Hyperopia." American Optometric Association Online?http://www.aoanet.org?.

Roach, Linda. "Correcting Hyperopia: Make Way for LTK." EyeNet Magazine Online?http://www.eyenet.org/eyenet_mag/02_01/refract.html?.

Sabbagh, Leslie. "Phakic IOLs Gaining Ground." Review of Ophthalmology Online?http://www.revophth.com/2001/January/January01PhakicTrial.htm?.