What are the four main types of refractive errors?
The four major types of refractive error are myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia. The most common refractive error is myopia or nearsightedness, whereby the light rays are focused in front of the retina. In astigmatism, irregular curvature of the cornea and lens results in the image being focused on different planes not coinciding with the retina. Hyperopia or farsightedness occurs when the light rays are not bent enough and the image is focused behind the retina. You can also have a combination of myopic astigmatism or hyperopic astigmatism. Presbyopia is a loss of the elasticity of the naturally occurring crystalline lens whereby individuals cannot focus clearly at close distances and need reading aids. This becomes apparent around the fourth decade of life.
