In an eye with normal vision, focusing ability of the cornea and lens is matched to the length of the eye. Your eyes are therefore able to focus an image precisely on the retina.
In nearsightedness, or myopia, vision is better up close than at a distance.
In farsightedness, or hyperopia, vision is often better at a distance than up close (although it may be blurry both at a distance and up close).
Both of these conditions are caused by structural distortions within the eye.
In myopia, your eyes focus the image ahead of the retina. This usually occurs with an eyeball that is longer or a cornea that is steeper than normal.
In hyperopia, your eye focuses the image behind the retina. This usually occurs if your eyeball is too short or the cornea has too little curvature. With aging, the lens of the eye becomes less flexible and cannot focus as well on close objects. This condition, called presbyopia, accounts for the development of difficulty seeing near objects in most people after the age of 40.
A risk factor is something that increases your chance of getting a disease or condition. Risk factors are slightly different for the two types of vision disorders.
Having a family member with myopia increases your risk for the disorder. Also, although the evidence is conflicting, some specialists believe that chronic near work, such as iprolonged periods of reading or the daily use of a computer can increase the risk of developing myopia.
There are two main risk factors for hyperopia:
Symptoms may include:
A vision specialist will ask about your symptoms and medical history. You will be given an eye exam and checked to see if prescription lenses will help improve your vision.
Treatment may include:
Most of the treatments for nearsightedness can be applied to hyperopia as well. Another common treatment is the use of reading glasses or bifocals, which are particularly useful for presbyopia. There are also collagen shrinkage (ie, conductive keratoplasty) techniques. For people undergoing cataract surgery (or refractive lens exchange surgery), intraocular lenses that correct for myopia or hyperopia and presbyopia are now available.
RESOURCES:
American Academy of Ophthalmology
http://www.aao.org
American Optometric Association
http://www.aoanet.org
National Eye Institute
National Institutes of Health
http://www.nei.nih.gov
CANADIAN RESOURCES:
Canadian Association of Optometrists
http://www.opto.ca/en/public
Canadian Ophthalmological Society
http://www.eyesite.ca
References:
Durrie DS, Vande Garde TL. LASIK enhancements. Int Ophthalmol Clin . 2000; 40:103.
Gimbel HV, Penno EE, van Westenbrugge JA, et al. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology . 1998;105:1839.
Harrison's Principles of Internal Medicine . 14th ed. McGraw-Hill;1998.
Shortt AJ, Bunce C, Allan BD. Evidence for superior efficacy and safety of LASIK over photorefractive keratectomy for correction of myopia (Review). Ophthalmology . 2006 Nov;113(11):1897-908.
Yoo SH, Azar DT. Laser in situ keratomileusis for the treatment of myopia. Int Ophthalmol Clin .1999;39:37.
Last reviewed November 2008 by Christopher Cheyer, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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