XI. What are the errors of refraction? How are they corrected? in special sense

Errors of refraction, also known as refractive errors, occur when the shape of the eye prevents light from focusing directly on the retina. The length of the eyeball (either longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors. There are four types of refractive errors:

1. Myopia (nearsightedness): This is a condition where the eye does not bend or refract light properly to a single focus to see images clearly. In myopia, close objects look clear but distant objects appear blurred.

2. Hyperopia (farsightedness): In hyperopia, distant objects may be seen more clearly than objects that are near. However, people experience hyperopia differently. Some people may not notice any problems with their vision, especially when they are young.

3. Astigmatism: Astigmatism is a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye. This can cause images to appear blurry and stretched out.

4. Presbyopia: This is an age-related condition in which the ability to focus up close becomes more difficult. As the eye ages, the lens can no longer change shape enough to allow the eye to focus close objects clearly.

Correction of these errors can be achieved through various methods:

1. Eyeglasses or contact lenses: These are the simplest and safest way to correct refractive errors. They work by refocusing light rays on the retina, compensating for the shape of your eye.

2. Refractive surgery: This can reduce or even eliminate your need for eyeglasses or contact lenses. The most common procedures are performed with an excimer laser. In these procedures, the cornea is reshaped so that it can focus light onto the retina.

3. Orthokeratology: This involves the fitting of a series of rigid contact lenses to reshape the cornea. The final lens in the series is left on for several hours a day to maintain the new shape. Fitting of the lenses is usually done by an optometrist.

4. Intraocular lenses: These are an alternative to correct refractive errors, especially for people with a high degree of hyperopia or myopia, or for those who are not good candidates for the laser procedures.

Remember, it's important to have regular eye examinations with an eye care professional. They can diagnose refractive errors as part of a comprehensive eye examination.