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Understanding Refractive Errors

Refractive error is a term you may have heard your optometrist mention during a recent eye exam. However like most medical terminology, the average person doesn’t always understand what the term means or how it applies to them.

Refractive errors occur from irregularities in the shape of the cornea – the outermost layer of the eye.  These irregularities make it difficult for the eye to focus and see clearly. Most often it leads to blurred vision, headaches, squinting and eye strain.

Myopia diagramThe four most common refractive errors are:


Myopia, also known as nearsightedness, affects one’s ability to see distant objects. It occurs when the cornea is too curved, causing light to be improperly refracted in front of the retina. When a person is nearsighted, objects close to the eye will appear clear but objects in the distance will appear blurry.


Hyperopia, also known as farsightedness, is the opposite of myopia. It’s caused when the cornea isn’t curved enough, causing light to be improperly refracted behind the retina.  When a person is farsighted, objects in the distance appear clear, while objects close to the eye appear blurry.


Astigmatism occurs when the cornea curves more in one direction than in another. It can happen in combination with myopia and hyperopia but can also exist on its own. When a person has astigmatism, both near and distant objects can appear blurry.


ContactsPresbyopia is similar to hyperopia in that it refers to the inability to focus on objects in the distance. However it occurs when the lens of the eye begins to lose its elasticity (typically around age 40) and happens naturally as we continue to age.

Refractive errors are typically treated with prescription eyeglasses or contacts. Each individual prescription is tailored to meet the needs of the patient and their specific refractive error. That’s why wearing another person’s glasses will not improve your vision.

Vision therapy is another treatment option for both children and adults. Vision therapy is an individualized program that pairs therapy sessions with at home exercises to help patients relearn or strengthen the use of various eye muscles.

Before any treatment can be prescribed, refractive errors must first be diagnosed via a comprehensive eye exam. To schedule an exam at The Eye Institute, please call 215.276.6000.