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Causes
By Mayo Clinic staff
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 objects
In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature like the surface of a rubber ball. A cornea and lens with such curvature bend (refract) all incoming light in such a way as to make a sharply focused image directly on the retina, at the back of your eye.
A refractive error
However, if your cornea or lens isn't evenly and smoothly curved, light rays aren't 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:
- 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.
- Care of the patient with hyperopia. St. Louis, Mo.: American Optometric Association. http://www.aoa.org/documents/CPG-15.pdf. Accessed Dec. 28, 2009.
- Refractive error. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec09/ch099/ch099a.html. Accessed Oct. 13, 2009.
- Frequency of ocular examinations. American Academy of Ophthalmology. http://one.aao.org/CE/PracticeGuidelines/ClinicalStatements_Content.aspx?cid=810eaf61-181e-41c8-a0e8-e1d122efe5a4. Accessed Oct. 14, 2009.
- Preferred practice patterns: Refractive errors and refractive surgery. American Academy of Ophthalmology. http://one.aao.org/CE/PracticeGuidelines/PPP_Content.aspx?cid=e6930284-2c41-48d5-afd2-631dec586286. Accessed Dec. 28, 2009.
- Opticians, dispensing. U.S. Department of Labor. http://www.bls.gov/oco/ocos098.htm. Accessed Dec. 28, 2009.
- Bower KS. Laser refractive surgery. http://www.uptodate.com/home/index.html. Accessed Oct. 14, 2009.
- Eye health tips. National Eye Institute. http://www.nei.nih.gov/healthyeyes/eyehealthtips.asp. Accessed Dec. 28, 2009.
- Robertson DM (expert opinion). Mayo Clinic, Rochester, Minn. Jan. 2, 2010.
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