Your eye has two parts that focus images:
- The cornea, the clear front surface of your eye
- The lens, a clear structure inside your eye that changes shape to help focus on objects
In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature, like the surface of a marble. A cornea and lens with such curvature bend (refract) all incoming light to make a sharply focused image directly on the retina, at the back of your eye.
A refractive error
If your cornea or lens isn't evenly and smoothly curved, light rays aren't bent (refracted) properly, and you have a refractive error. Farsightedness is one type of refractive error.
Farsightedness occurs when your cornea is curved too little or your eye is shorter than normal. Instead of being focused precisely on your retina, light is focused behind your retina, resulting in a blurry appearance for close-up objects.
Other refractive errors
In addition to farsightedness, other refractive errors include:
April 09, 2015
- Nearsightedness (myopia). This occurs when your cornea is curved too much or your eye is longer than normal, which makes faraway objects blurry and close objects clear.
- Astigmatism. This occurs when your cornea or lens is curved more steeply in one direction than in another. Uncorrected astigmatism blurs your vision.
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- Overview of refractive error. The Merck Manual Professional Edition. http://www.merckmanuals.com/professional/eye_disorders/refractive_error/overview_of_refractive_error.html?qt=refractive error&alt=sh. Accessed March 17, 2015.
- Frequency of ocular examinations - 2015. American Academy of Ophthalmology. http://one.aao.org/clinical-statement/frequency-of-ocular-examinations--november-2009. Accessed March 17, 2015.
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- Eye health tips. National Eye Institute. https://www.nei.nih.gov/healthyeyes/eyehealthtips. Accessed March 17, 2015.
- Robertson DM (expert opinion). Mayo Clinic, Rochester, Minn. March 28, 2015.
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