Hyperopia or farsightedness affects 5—25 percent of the population. People with hyperopia see objects in the distance clearly but have difficulty seeing up close. If not corrected, hyperopia can cause amblyopia (lazy eye) or strabismus (crossed eye). Treatment for hyperopia includes eyeglasses, contacts, or surgery.
Hyperopia has a genetic component, can be passed down in families, and exists in all races. Evidence of hyperopia can be found as early as the 1200s in Italy where early eyeglasses were created. These early glasses had lenses that were convex-shaped disks, which would be appropriate for correcting hyperopia.
A convex lens corrects hyperopia by compensating for the eye structures that are not focusing images correctly. Light rays must be focused by the structures of the eye in order to project a clear image on the retina. The cornea and lens of the eye focus light as it travels to the retina. A hyperopic eye is too short to allow the light rays to bend enough to arrive focused at the retina. Alternatively, a hyperopic eye may have a flatter cornea or insufficient lens power. If corrective lenses are not used to focus the image, the image would be in focus behind the retina.
Advances in the past two centuries have improved the early convex lenses to allow precise calibration. The amount of correction needed is measured in diopters. A person who is farsighted needs a convex lens denoted by a plus sign preceding the diopter strength. Digital aspheric lenses minimize distortion and make eyeglasses lighter.
Types and Symptoms
The AOA (American Optometric Association) divides hyperopia into three clinical categories: simple hyperopia, pathological hyperopia, and functional hyperopia (Moore et al., 2008). Simple hyperopia results from an eye that is too short, a flattened cornea, or an abnormal lens. Pathological hyperopia results from changes in eye anatomy caused by developmental problems, eye diseases, or eye injury. Functional hyperopia results when muscles in the eye become paralyzed.
Additionally, hyperopia can be categorized by severity: low hyperopia, moderate hyperopia, and high hyperopia. Low hyperopia can be corrected with lenses of 2 diopters or less. Patients with low hyperopia may be able to accommodate on their own without correction. Moderate hyperopia requires +2.25 to +5 diopters of correction. While patients with moderate hyperopia may be able to function with uncorrected vision, they may have difficulty with close work and experience eye fatigue and headaches. High hyperopia requires greater than 5 diopters of correction and working at near distances without correction becomes difficult for these patients.
Symptoms of hyperopia include difficulty seeing clearly up close, eyestrain, eye fatigue, headaches, and squinting. Young children may have asymptomatic hyperopia, called developmental or age-appropriate hyperopia. Most children have some degree of farsightedness, which often self-corrects as the eyes grow.
Glasses or contact lenses are common treatment options for hyperopia. Digital aspheric lenses have been developed that provide less distortion and thinner lenses. Contact lenses can be placed directly on the cornea to bend light rays and help the image focus on the retina.
More recently, surgical techniques have been developed to correct hyperopia. During LASIK (laser-assisted in situ keratomileusis) surgery a flap of corneal tissue is removed, the cornea is reshaped, and the flap is replaced. PRK (photorefractive keratectomy) surgery also uses a laser to reshape the cornea, but the laser is applied directly to the cornea without creating a flap. Phakic intraocular lens surgery places a new lens in front of the existing lens, whereas refractive lens exchange surgery replaces the patient’s lens entirely.
Hyperopia treatment with glasses, contacts, or surgery leads to positive outcomes as measured by restored vision in most cases. Surgical outcomes for hyperopia vary depending on the severity, cause, and techniques used.
In contrast to patients with successfully treated hyperopia, children with untreated hyperopia are at risk for amblyopia (lazy eye) and strabismus (crossed eye), two conditions that can lead to permanent vision loss. Patients with hyperopia also have an increased risk for acute angle-closure glaucoma, which can cause optic nerve damage and blindness.
Research is ongoing to discover additional therapies and interventions for patients with hyperopia. Just as digital aspheric lenses have created thinner, lighter eyeglasses with less distortion, additional advances may provide better lenses. Contacts also continue to improve with extended-wear and disposable lenses now available. Surgical outcomes may be developed for farsighted patients. Additional screening methods may be developed to identify children with significant hyperopia so that fewer children develop complications that compromise vision.
Lisa A. Rabe
See also: Accommodation; Amblyopia; Blindness; Strabismus
Moore, Bruce D., et al. (2008). Care of the patient with hyperopia. American Optometric Association. Retrieved from http://www.aoa.org/documents/optometrists/CPG-16.pdf