• Nearsightedness and Farsightedness

    (Myopia and Hyperopia)

    Definition

    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).
    Myopia
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    Causes

    Both of these conditions are caused by structural distortions within the eye.

    Myopia

    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.

    Hyperopia

    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.

    Risk Factors

    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.

    Myopia

    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.

    Hyperopia

    There are two main risk factors for hyperopia:
    • Age: 40 or older (hyperopia due to presbyopia )
    • Family member with hyperopia

    Symptoms

    Symptoms may include:

    Myopia

    • Blurred vision of distant objects
    • Squinting
    • Eyestrain
    • Headaches

    Hyperopia

    • Blurred vision of close and often distant objects
    • Need for more light while working
    • Eye fatigue
    • Headaches

    Diagnosis

    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

    Myopia

    Treatment may include:
    • Eyeglasses
    • Soft contact lenses
    • Laser in situ keratomileusis (LASIK) —the use of a laser to permanently reshape the cornea by etching away cells beneath its surface (the most common surgical treatment for myopia)
    • Laser epithelial keratomileusis (LASEK)—a procedure that is quite similar to LASIK, but differs in a technique of removal of the first layer of cornea. LASEK supposedly offers benefits over the typical LASIK procedure in terms of faster healing time and decreased post-surgical pain. Those benefits have been however questioned by recent studies. More research is needed to clarify the benefits of the LASEK procedure.
    • Epi LASIK procedure (Epithelial laser-assisted in situ keratomileusis )—a hybrid procedure that combines elements of both LASEK and LASIK.
    • Photorefractive keratectomy (PRK)—the use of a laser to permanently reshape the cornea by removing cells on its surface (less commonly done)
    • Radial keratotomy (RK)—the use of microincisions to flatten the cornea (rarely done)
    • Intraocular lenses—in some situations, removing your native lens and possibly replacing it with an intraocular lens can help treat myopia
    Risks and Complications of Surgical Procedures
    • Under- and over-correction
    • Astigmatism
    • Visual problems such as glare or double vision
    • Dry eyes
    • Post-surgical problems with healing and/or infections
    • Long-term complications (more than 10 years of follow-up) are unknown at this time

    Hyperopia

    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.

    Prevention

    There are no guidelines for the prevention of myopia or hyperopia.

    RESOURCES

    American Academy of Ophthalmology http://www.aao.org/

    American Optometric Association http://www.aoa.org/

    National Eye InstituteNational Institutes of Health http://www.nei.nih.gov/

    CANADIAN RESOURCES

    Canadian Association of Optometrists http://www.opto.ca/

    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.

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