Refractive Errors

When an eye has an irregular shape, it keeps light from focusing correctly on your retina (a light-sensitive layer of tissue in the back of your eye). This is called a refractive error, and it can make it difficult to see clearly.

Refractive errors are the most common type of vision problem. More than 150 million Americans have a refractive error — but many don’t know that they could be seeing better. That’s why eye exams are so important.

If you have a refractive error, your eye doctor can prescribe eyeglasses or contact lenses to help you see clearly.

4 Most Common Types of Refractive Errors

Nearsightedness (Myopia)

Myopia, or nearsightedness, is a vision condition in which close objects are seen clearly, but objects farther away appear blurred. Nearsightedness occurs if the eyeball is too long or the cornea, the clear front cover of the eye, has too much curvature. As a result, the light entering the eye is not focused correctly and distant objects look blurred. Nearsightedness is a very common vision condition affecting nearly 30 percent of the U.S. population. Some research supports the theory that nearsightedness is hereditary.  There is also growing evidence that it is influenced by the visual stress of too much close work.

Farsightedness (Hyperopia)

Hyperopia, or farsightedness, is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly. Common signs of farsightedness include difficulty in concentrating and maintaining a clear focus on near objects, eye strain, fatigue and/or headaches after close work, aching or burning eyes, irritability or nervousness after sustained concentration.

Astigmatism

Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or the irregular curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance. Astigmatism is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually do not affect vision and do not require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort and headaches.

Presbyopia

Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility, which makes it difficult for you to focus on close objects.

Presbyopia may seem to occur suddenly, but the actual loss of flexibility takes place over a number of years. Presbyopia usually becomes noticeable in the early to mid-40s. Presbyopia is a natural part of the aging process of the eye. It is not a disease, and it cannot be prevented.