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Johns Hopkins Symptoms and Remedies

Johns Hopkins Medicine

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Refractive Disorders

In a normal eye, light focuses precisely on the retina. In nearsightedness, light focuses just short of the retina; in farsightedness, just beyond the retina.

What is it?

Refractive disorders—which include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism— are common, correctable vision problems linked to certain structures in the eye. Light enters the eye through the cornea, the thin, transparent membrane in the front of the eye, and then passes through the pupil, the dark area in the center of the iris. The shape of the cornea, its curve, begins the focusing process of the eye. The lens, located behind the pupil, further focuses the light rays onto the retina, the layer of light-sensitive cells that line the back of the eye. Refractive disorders arise when irregularities in the shape or refractive strength of these structures focus the image in front of or behind the plane of the retina.When this occurs, vision becomes blurred. In myopia, objects at a distance appear out of focus; in hyperopia, objects nearby and at a distance are unclear. In astigmatism, the cornea is unevenly curved, producing blurriness or varying degrees of distortion in portions of the visual field. Astigmatism may be combined with either myopia or hyperopia in the same eye. In addition, after age 40, the lens becomes progressively less flexible and the eye muscle that adjusts the lens shape weakens, impairing close vision (see Presbyopia). Refractive disorders may be corrected with glasses, contact lenses, intraocular implants, or laser surgery.

What Causes It?

  • Hereditary factors play a role.

Prevention

  • Recognizing and treating refractive disorders is important in order to prevent or treat amblyopia— reduced vision in one or both eyes because of understimulation—in children.
  • Contrary to popular belief, vision cannot be improved by refusing to wear glasses if you need them or by performing so-called eye exercises.
  • Safety goggles designed to protect eyes during sports or that are required for specific occupations can have prescription lenses incorporated in them.

Diagnosis

  • An ophthalmologist will perform an eye examination and determine your eyeglass measurement (refractive error).

How to Treat It

  • Glasses or contact lenses are prescribed to correct vision. The prescription may require updating if vision changes.
  • Two types of laser surgery have been developed to change the location of where the eye focuses an image: PRK (photorefractive keratectomy) and LASIK (laser-assisted in-situ keratomileusis). Both types of surgery make use of a special machine known as an excimer laser to produce pulses of light energy that can alter the shape of the cornea so that light rays from distant objects will focus on the retina with greater precision. Both procedures can be performed to correct myopia, hyperopia, astigmatism, and presbyopia. An older form of surgery, known as radial keratotomy (RK), which helps correct mild to moderate myopia, is now used infrequently.

When to Call a Doctor

  • Make an appointment with an ophthalmologist or optometrist if you or a child has vision problems.