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Vision


Vision

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Refractive Disorders

Symptoms

Blurred vision at a distance (myopia).

Blurred vision of nearby objects and difficulty reading, possibly causing eyestrain and headaches (hyperopia).

Uneven degrees of blurriness in portions of the visual field (astigmatism).

When To Call Your Doctor

Make an appointment with an ophthalmologist or optometrist if you have vision problems.


What Are They?

Refractive disorders—which include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism—are common, correctable vision problems. Light enters the eye through the cornea, the thin, transparent membrane covering the eye, and then the pupil, the dark area in the center of the iris. The lens, located behind the pupil, 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 distort the focus and impair vision.

In myopia, objects at a distance appear out of focus; in hyperopia, nearby objects 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, the lens becomes progressively less flexible after age 40, impairing close vision. Refractive disorders may be corrected with glasses, contact lenses, or laser surgery.

What Causes Them?

Hereditary factors play a role.

Prevention

Contrary to popular belief, vision cannot be improved by refusing to wear glasses if you need them or by performing so-called eye exercises.

Diagnosis

An ophthalmologist will perform an eye examination and determine your eyeglass measurement.

How to Treat Them

Glasses or contact lenses are prescribed to correct vision. The prescription is updated as vision changes.

Two types of laser surgery have been developed to sharpen vision: PRK (photorefractive keratectomy) and LASIK (laser-assisted in-situ keratomileusis). They use 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.

Wear goggles to protect your eyes or a sports strap to secure glasses during sports and strenuous activities.

 

From Johns Hopkins Symptoms and Remedies, the complete home medical reference. You can order this book now on our secure server.

 

 


 


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2005
WHITE PAPERS
Vision

The vision White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.


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Johns Hopkins Symptoms and Remedies
An easy-to-use reference work that can help you pinpoint the cause of hundreds of symptoms, from abdominal pain to skin rash to swollen glands.

 

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