What is Farsightedness? Can LASIK Correct Farsightedness?

Farsightedness is a refractive error caused by the cornea being too flat for the eye. LASIK can correct farsightedness very effectively. Farsightedness should not be confused with presbyopia, the age-related loss of the ability to see up close.

A patient from Camarillo recently told me she was farsighted, but never quite understood what that meant. Worse yet, she said, her eyes appeared to be getting worse both at close and in the distance ever she entered her 40’s.

Farsightedness is a much more tricky concept to understand than nearsightedness. Nearsighted patients, without glasses or contacts, can see near but not far — hence the word “nearsighted.” One would think farsighted people would therefore see remarkably well far away, but the situation is actually quite a bit more complicated than this.

First, it is important to understand the difference between farsightedness and presbyopia, the age-related loss of the ability to see up close. “Presbyopia” comes from the Greek words for “aging of the eye.” It happens because the lens of the human eye gets stiffer once a person passes the age of 40. The job of the lens is to flex or bulge to see up close and then relax to see in the distance. As the lens gets stiffer, it has difficulty focusing for close, but is still able to remain relaxed and un-flexed for distance focus. Many people inappropriately call this process “getting farsighted” since the distance remains good and only the close deteriorates. The reality is that being farsighted is not related to age: someone who is farsighted typically has been farsighted their entire life and doesn’t become farsighted only after age 40. Also, people over age 40 can be either nearsighted (myopic), farsighted (hyperopic), or have perfect sight (emmetropic). All of these people, however, will develop presbyopia as their lens naturally stiffens with age.

The cornea is the clear domed cap of the eye, similar to the cover of a watch. True farsightedness is due to a flaw in the shape of the cornea, not to aging. As such, like nearsightedness, farsightedness is called a “refractive error” of the eye. In the case of farsightedness, the corneal curvature is too flat for the eye. Like the cover of a watch, the cornea is a clear structure. Clear structures focus light by virtue of their curvature. An flat, clear structure like a window pane does not focus light as it passes through it. A raindrop, by contrast, focuses light because it is curved and clear. The more curvature there is, the more the light is focused. Because the cornea is too flat in a farsighted, or hyperopic, eye, light entering the eye is focused too weakly and has not yet come to a point of focus by the time it hits the retina. In the case of nearsightedness, the cornea is too steeply curved and focuses the light rays too powerfully, so that they come to a point of focus before they reach the retina. In a perfect, or emmetropic, eye, the corneal curvature is perfect for the eye and the light rays are appropriately focused to a point on the retina.

Remember, if a person only has presbyopia, then when their lens is relaxed, the person should see very clearly at distance regardless of age. If a person is farsighted, however, and their cornea is too flat so it does not focus light passing through it, then when the lens is relaxed, the focus is not at distance as it should be. Rather, when the lens relaxes in a person with a cornea like this, the focus is too far — i.e. beyond distance — hence the name “farsightedness.” One might think this would be a good thing — that very far objects would be sharp — but the opposite is true. If you are in focus beyond the distance, then you are, of course, not in focus at distance itself — and distance objects are blurry.

The only way for a farsighted person to see clearly in the distance is to flex the lens to bring the focus inward to distance itself. To look at the Channel Islands across the ocean, therefore, a farsighted person must flex their lens much like a “normal” person does to read. In order to see in the mid-range — say the dashboard of a car — this same person must flex even more, whereas the “normal” person is only starting to flex their lens. To see up close to read, the farsighted person must flex their lens even more. For this reason, unlike the case for the “normal” person, the farsighted person needs to flex their lens for any point in space they look — at close, in the mid-range, and in the distance. As the lens gets stiffer with age and presbyopia, of course, all three of these tasks get more difficult.

Fortunately, LASIK and PRK offer laser vision correction options that can correct farsightedness by re-shaping the cornea. In correcting farsightedness, the laser sculpts the sides of the cornea to make it steeper, correcting the overly flat corneal shape that causes farsightedness. So, yes, LASIK and PRK can very successfully correct farsightedness!

Remember, though, that having laser eye surgery to correct farsightedness, whether LASIK or PRK laser vision correction, will not make you any younger. If you are at an age in which you are developing presbyopia, correcting your farsightedness will improve your vision. If you also are interested in treating presbyopia, then additional options include the use of monovision and blended vision laser eye surgery.

What is Farsightedness? Can LASIK Correct Farsightedness?

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