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Understanding refractive errors of a human eye

  • Posted on- Oct 15, 2015
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The function of the eye is to see the objects around us clearly. Normally, light rays are refracted by the cornea and lens and focus directly on the retina, the nerve layer at the back of the eye, which results in clear vision. The inability of the eye to accurately focus the rays of light coming from distance on the retina is called refractive error. In most cases, refractive errors represent a natural variation from normal vision and are not considered a disease. Nearsightedness, farsightedness, astigmatism, and presbyopia are common refractive errors.

Farsightedness: Hyperopia or farsightedness results when light entering the eye focuses behind the retina instead of directly on it. This is often due to a cornea which is flatter than a normal eye. A person with hyperopia will experience difficulty seeing objects that are close and may experience eyestrain and headaches after reading or doing close work. The condition will generally worsen with age, as the eye loses its ability to concentrate.

Myopia: Myopia or nearsightedness occurs when the eye focuses in front of the retina as opposed to directly on it. This effect is generally caused by a cornea that is steeper than a normal eye. Typical symptoms are blurry distance vision which may make the reading of highway signs, blackboards, etc. difficult. It is estimated that as much as a third of the population (world) may suffer from myopia.

Astigmatism: Astigmatism occurs when the cornea is more oval than spherical. The corneal surface may in addition have some areas which are flatter or steeper than others. Depending upon the degree, symptoms of astigmatism may include distortion in areas of your field of vision, blurring of lines, eyestrain, and headaches. It may co-exist with other refractive errors as well.

Presbyopia: Presbyopia is the normal aging process, where the lens progressively loses its capacity to increase its power for near vision. The distance vision may be normal, but the near vision becomes blurred with aging. This condition may occur in itself or may be present along with pre-existing myopia, hypermetropia or astigmatism.

Different ways of treating refractive errors
 

The refractive errors may be treated by either of the following ways:

  • Wearing glasses is the simplest and most popular way of correcting refractive errors.
  • Applying contact lenses is another option which is cosmetically much better though the maintenance and cleaning of contact lenses may be burdensome. There is also a slight risk of infection to the cornea, if the contact lenses are not cleaned properly before use.
  • Refractive surgeries are increasingly becoming popular with the arrival of more predictable laser treatments.

Various refractive surgeries

The refractive power of the eye can be changed with the following approaches:
  • Changing the curvature of the cornea- a popular mode of refractive surgery.
  • Removing the natural lens and replacing it with an artificial lens of adequate power.
  • Putting an additional artificial lens within the eye on top of the existing natural lens.

Most of the refractive errors may be corrected with eyeglasses or contact lens. A more permanent solution for many individuals exists with a laser eye surgery procedure such as LASIK. In many cases a laser surgical procedure can eliminate the need for glasses or contacts. In any case, it is of extreme importance that any and all vision problems be thoroughly assessed by a qualified ophthalmologist who can advise the best course of treatment.