Refractive errors

Refractive error is an optical term. When our eyes have a refractive error, it is out of focus. Glasses or contact lenses usually are able to correct refractive errors and help our vision to become more clear. There are several types of refractive errors. The most common are:

  • Hyperopia, or “far-sightedness”. In hyperopia, the light entering the eye is focused at a point past the eye. This condition usually occurs because the eye is a little shorter than it should be. Lenses that bend the light rays so that the focus point is brought back onto the retina inside the eye are needed to correct this problem.
  • Myopia, or “near-sightedness”. In myopia, the problem usually is that the eye is longer than it should be.  Lenses that lengthen the path of the light rays to move the focus point onto the retina are needed to correct this problem. To find out more about myopia, click here: http://www.geteyesmart.org/eyesmart/diseases/myopia.cfm
  • Astigmatism. How astigmatism causes the eye to be out of focus is a little more complex to understand. There are two types of astigmatism, irregular and regular. Irregular astigmatism is usually due to a medical condition, and fortunately is much less common than regular astigmatism. In regular astigmatism, all of the light rays entering the eye are not focused on the same point. Lenses that are designed to correct astigmatism by selectively focusing the different light rays are called toric lenses. Astigmatic correction can be found in eye glasses, contact lenses, and even in intraocular lens implants. For more information about astigmatism, please click here: http://www.geteyesmart.org/eyesmart/diseases/astigmatism.cfm
  • Presbyopia. Presbyopia means “old eye”, and is the reason why many people need to use glasses for reading when they reach their 40’s or 50’s. It is commonly thought that presbyopia is due to loss of flexibility of the natural lens in the eye, so that the lens cannot change shape to focus on objects as they are brought closer to the eye. To find out more about presbyopia, click here: http://www.geteyesmart.org/eyesmart/diseases/presbyopia.cfm