Nearsightedness usually occurs when your eye is too long or has a cornea that's curved too steeply. This causes the light rays entering each eye to focus in front of the retina, instead of on the retina, leading to blurry images. The exact reason for some people developing longer eyes is unknown, but it may be related to genetics or environmental conditions.
To focus the images it sees, your eye relies on two critical parts:
- The cornea, the clear front surface of your eye
- The crystalline lens, a clear structure inside your eye that changes shape to help focus objects
In a normally shaped eye, each of these focusing elements has a perfectly smooth curvature like the surface of a smooth 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 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. Nearsightedness is one type of refractive error. Instead of being focused precisely on your retina, light is focused in front of your retina, resulting in a blurry appearance of distant objects.
Other refractive errors
In addition to nearsightedness, other refractive errors include:
March 04, 2015
- Farsightedness (hyperopia). This occurs when your cornea is curved too little or your eye is shorter from front to back than normal. The effect is the opposite of nearsightedness. In adults, both near and distant objects are blurred.
- Astigmatism. This occurs when your cornea or lens is curved more steeply in one direction than in another. Uncorrected astigmatism blurs your vision.
- Preferred practice patterns: Refractive errors and refractive surgery summary benchmark — 2014. American Academy of Ophthalmology. http://one.aao.org/summary-benchmark-detail/refractive-errors--surgery-summary-benchmark-octob. Accessed Jan. 19, 2015.
- Myopia (nearsightedness). American Optometric Association. http://www.aoa.org/myopia.xml. Accessed Jan. 19, 2015.
- Refractive error. The Merck Manual Professional Edition. http://www.merckmanuals.com/professional/eye_disorders/refractive_error/overview_of_refractive_error.html. Accessed Jan. 19, 2015.
- Frequency of ocular examinations — 2009. American Academy of Ophthalmology. http://one.aao.org/clinical-statement/frequency-of-ocular-examinations--november-2009. Accessed Jan. 19, 2015.
- Mian SI. Visual impairment in adults: Refractive disorders and presbyopia. http://www.uptodate.com/home. Accessed Jan. 19, 2015.
- Opticians, dispensing. U.S. Department of Labor. http://www.bls.gov/ooh/healthcare/print/opticians-dispensing.htm. Accessed Jan. 19, 2015.
- Eye health tips. National Eye Institute. http://www.nei.nih.gov/healthyeyes/eyehealthtips.asp. Accessed Jan. 19, 2015.
- Morgan IG, et al. Myopia. The Lancet. 2012;379:1739.
- Myopia (adult and pediatric). AskMayoExpert. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2014.
- Refractive error. AskMayoExpert. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2015.
- Nearsightedness. American Academy of Opthalmology. http://www.geteyesmart.org/eyesmart/diseases/myopia-nearsightedness/index.cfm. Accessed Jan. 19, 2015.
- Barbara Woodward Lips Patient Education Center. Surgery to improve your vision: PRK and LASIK. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2008.
- Myopia (Nearsightedness). American Optometric Association. http://www.aoa.org/patients-and-public/eye-and-vision-problems/glossary-of-eye-and-vision-conditions/myopia?sso=y. Accessed Jan. 20, 2015.
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