Vision Correction Surgery
Vision Correction Surgery Introduction
Refractive surgery for vision correction has made tremendous advances over the last half century. One of the earliest methods involved the creation of deep incisions in the cornea to result in intentional weakening and shape alteration for corrective purposes. Radial keratotomy, or RK, was one of the first incisional refractive procedures. The concept was first used more than 50 years ago by Sato at Juntendo University in Japan. The original procedure involving posterior internal incisions, however, didn't work for most people, and many patients suffered from bullous keratopathy in later years.
RK was subsequently modified to avoid direct damage to the corneal tissues and evolved as the earliest form of vision correction surgery. It was perfected in the 1970s by the Russian ophthalmologist Fyodorov and was first performed in the United States in 1978.
Today, many different options exist to help the majority of people who wear glasses or contact lenses reduce or eliminate their dependence on their corrective lenses. In almost all cases, refractive surgery is elective and cosmetic.
- Vision correction surgery can benefit people with myopia (nearsightedness), hyperopia (farsightedness), and astigmatism, and in the future, presbyopia.
- Myopia occurs when near objects appear clear but distant objects are blurry. The eye is too long and/or the cornea is too steep for its focusing ability, thus, objects are blurry.
- Hyperopia occurs when near objects are blurry and far objects are clear. In this case, the eye is too short and/or the cornea is too flat for its focusing ability, which causes the blurriness.
- Astigmatism is best described as distorted or warped vision due to the surface of the eye being somewhat irregular in shape. With this condition, the eye has various focal points causing images to be distorted.
- Presbyopia (Greek word presbys (πρέσβυς), meaning "old person") describes the condition in which the eye exhibits a progressively diminished ability to focus on near objects with age.
- Vision correction surgery modifies the cornea and/or the lens in order to focus light on the back of the eye without the need for corrective lenses.
- Vision correction surgery will usually not benefit people with presbyopia (the inability to see objects up close). This condition affects all people older than 40-45 years of age and is corrected by bifocal glasses or bifocal contact lenses. In presbyopia, the lens loses its ability to change shape and thus focus the eye on objects up close. Presbyopia is not a problem of the eye being too long or too short. Research is ongoing to develop corrective surgical procedures for presbyopia, but the technique has not yet been established.
Today, various options in vision correction surgery include the following:
- radial keratotomy (RK)
- laser vision correction
- photorefractive keratotomy (PRK)
- laser in situ keratomileusis (LASIK)
- femtosecond laser-assisted LASIK (iLASIK)
- laser thermal keratoplasty (LTK)
- conductive keratoplasty (CK)
- intracorneal ring segments (ICR)
- phakic intraocular lens implants
- PRELEX (presbyopic refractive lens exchange) or clear lens extraction
Who is a candidate for laser vision correction? Laser vision correction can be used to treat myopia, myopia with astigmatism, hyperopia, hyperopia with astigmatism, or mixed astigmatism. Not every person requesting laser vision correction is a candidate for the surgery. Factors, such as very high refractive errors (prescriptions), certain ocular diseases, certain medical diseases, and previous history of ocular surgery may prevent a person from being a candidate for refractive surgery.
- Criteria for laser vision correction: The following are general criteria which may vary according to the laser machine used and with modifications of criteria which could depend upon institutional or the individual surgeon's preferences.
- age 18 years or older for myopia or hyperopia
- age 21 years or older for astigmatism
- stable refraction for at least one year, meaning that the individual's glass or contact lens prescription has not changed. Some surgeon's may require waiting for lesser periods, such as several weeks.
- myopia between -0.50 and -14.00 diopters (If more than -14.00 diopters, a clear lens extraction is considered.) (Diopter is the unit of measurement of glasses or contact lenses; higher numbers are stronger prescriptions.)
- astigmatism <5.00 diopters
- hyperopia <+6.00 diopters
- no eye problems, such as keratoconus, herpes keratitis, unstable refractive error, corneal disease/scarring, or cataract/glaucoma
- no medical problems, such as collagen vascular diseases (lupus), autoimmune diseases (rheumatoid arthritis), immunosuppressive diseases (AIDS), no keloid formation during wound healing, no diabetic retinopathy if diabetes is present
- not taking medications such as Accutane, Imitrex, or amiodarone
- pregnant and nursing
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