When light passes through the lens and cornea of the eye, its velocity decreases. The surfaces of the lens and cornea are not perpendicular to the incoming light, so the direction of the light changes. The greater the curvature of the lens system, the greater the change in the direction of the light.
When parallel light rays pass through the lens system of the eye, they are bent so they converge at a point some distance behind the lens. With perfect vision, this point of convergence where the light rays are focused lies on the retina. Hyperopia is the condition in which the point of
focus of parallel light rays from an object lies behind the retina. This condition exists when the eyeball depth is too short for the curvature of its lens system.
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 look at a close object). A good example is during reading, when the lens accommodates to make the close-up material clear and the eyes turn in to look at the print and keep it from doubling. Because of this connection between accommodation and convergence, if the lens needs to accommodate and focus for distance (to bring the image back onto the retina), the eyes may appear to turn in.
Causes & symptoms
Babies are generally born slightly hyperopic, but this symptom tends to decrease with age. There is normal variation in eyeball length and curvature of the lens
Symptoms depend on the degree of hyperopia. Some individuals may have no symptoms, while others have blurry near vision and clear distance vision, and those with the most severe cases have blurry near and distance vision. Headaches and eyestrain may also occur, particularly when doing close work. An eye turned in (esotropia) may be a result of hyperopia, particularly in children. A turned eye could also signal a more serious problem, so a physician should be consulted.
Because it is possible to have good visual acuity with some degree of hyperopia it, is important to relax accommodation before an eye exam. This is done with the use of eye drops and is called a cycloplegic exam, or cycloplegic refraction. The patient's visual status can be determined with a hand-held instrument called a retinoscope and/or by having the patient read from an eye chart while placing different lenses in front of the patient's eyes. The patient should be driven home after such an exam because the drops cause blurred vision for several hours.
Bilberry (Vaccinium myrtillus) increases the flow of blood through the vessels of the eye. Eye drops of eyebright (Euphrasia officinalis) tea can relieve eye-strain and, taken orally with rosemary (Rosemarinus officinalis) in white wine, can improve vision. Schisandra (Schisandra chinensis) improves visual clarity.
Persons whose vision changes according to their emotional state may have vision problems because of negative conditioning. Exploration and deconditioning may improve their vision.
Head massage and nasya (placing drops in the nose) using warm Jivantal taila oil (which contains Asparagus racemosus, Glycyrrhiza glabra, Leptadenia reticulata, Sida cordifolia, Sida retusa, and sesame oil) may improve vision in persons who are hyperopic.
Performing qiqong eye exercises significantly reduced hyperopia in children. In another study, children with hyperopia were cured following treatment with plum-blossom needle tapping plus external application of Huoxue Zengshi Ye (Infusion for Promoting Blood Circulation and Improving Eyesight) and Huoxue Zengshi Dan (Pellets for Promoting Blood Circulation and Improving Eyesight).
The Bates method involves the use of therapeutic eye exercises to help strengthen and train the eye muscles. Some patients have found the eye exercises to help, although the method has not been tested in a clinical setting.
Other movement exercises or disciplines can be useful including massage, Feldenkrais movement therapy, yoga and t'ai chi. A practitioner should be consulted to determine what would be most helpful for particular individuals.
The usual treatment for hyperopia is corrective lenses (spectacles or contact lenses). Special contact lenses (vision orthotics) that are worn overnight temporarily re-shape the cornea for ideal vision on the following day.
There are now several different surgical methods used to correct hyperopia. One approach is to implant corrective contact lenses behind the patient's iris. Another approach, called laser in situ keratomileusis (LASIK), is to surgically increase the curvature of the eye's existing cornea or lens using a laser. Many surgeries are successful,
In mid-2002, the Food and Drug Administration (FDA) approved a new surgical technique to correct hyperopia. Called conductive keratoplasty, it involves no cutting or removal of tissue. An ophthalmologist uses a small probe about the size of a human hair to pass radiofrequency waves that produce heat into the corneal tissue. The waves shrink the tissue and reshape the cornea.
The prognosis for fully corrected vision is excellent for patients with low to moderate degrees of hyperopia. Patients with very high hyperopia may not achieve full correction.
Hyperopia is usually present at birth and cannot be prevented. Eyestrain may be prevented by resting the eyes when they become overworked, blinking often, and periodically changing the eyes' focus while driving or doing close work for extended periods of time.
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American Academy of Ophthalmology. PO Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.eyenet.org/.
American Optometric Association. 243 North Lindbergh Boulevard, St. Louis, MO 63141. (800) 365-2219. http://www.aoanet.org/.
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Teresa G. Odle