Indira Gandhi Eye Hospital and Research Centre
Indira Gandhi Eye Hospital and Research Centre
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Refractive Errors

Light rays from an image travelling through the eye's optical system are refracted and focused into a point of sharp focus that ideally should centre on the retina. The retina is the tissue that lines the inside of the back of the eye, where light-sensitive cells (photoreceptors) capture images in much the same way that film in a camera does when exposed to light. These images then are transmitted through the eye's optic nerve to the brain for interpretation. Just as a camera's aperture is used to adjust the amount of light needed to expose film in just the right way, the eye's pupil widens or constricts to control the amount of light that reaches the retina. The eye's inability to refract or focus light sharply on the retina results in refractive errors.

Types of refractive errors

Myopia or nearsightedness

When the eye is too long, images mistakenly focused in front of the retina are out of focus by the time they actually hit the retina. This causes myopia.

Hyperopia or farsightedness

When the eye is too short, images never have a chance to achieve focus by the time they hit the retina. This causes hyperopia.

Astigmatism

If the cornea is not perfectly spherical, then the image is refracted or focused irregularly to create a condition called astigmatism. A person can be nearsighted or farsighted with or without astigmatism.

Symptoms

The primary symptom of refractive errors is blurred vision for distant objects, near objects, or both. Occasionally, headaches, eye irritation, itching, visual fatigue, foreign body sensation, and redness also indicate refractive errors. Frowning when reading and excessive blinking or rubbing of the eyes are symptoms in children.

Treatment

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

Glasses

This is the simplest and most popular way of correcting refractive errors.

Contact lens

This option is cosmetically much better though the maintenance and cleaning of contact lenses may be cumbersome. There is also a slight risk of infection to the cornea, if the contact lenses are not cleaned properly before use.

Refractive surgeries

These are increasingly becoming popular with the advent of more predictable laser treatments, especially LASIK surgery. Utilising the accuracy and precision of the computer controlled excimer laser, LASIK changes the shape of the cornea and corrects refractive errors.