Refractive surgery is an elective procedure designed to correct the curvature of the cornea. Many people choose this method because they are tired of wearing glasses or contact lenses.
Typical candidates for either LASIK or PRK surgeries are healthy adults between the ages of 18 and 55 whose vision has not changed in the past year and who have mild to moderate nearsightedness, farsightedness, or astigmatism. Those who may not qualify are those with dry eyes, cataracts, or other eye problems, or if pregnant as vision often changes during pregnancy.
Those with nearsightedness should be no more than -14.00 diopters (-12.00 for PRK). This can be with, or without, astigmatism between -.50 and -5.00 diopters (-.75 and -4.00 for PRK).
Those with farsightedness, should be no more than +6.00 diopters. Eligibility exams usually require a minimum of two hours. With either procedure, expect to be in the doctor’s office up to two hours; and follow-up appointments are routinely one day, one week, one month, and one year following the surgery.
Refractive keratology was the first type of refractive surgery to reshape the cornea but has been widely replaced by PRK and LASIK surgeries. Refractive keratology was developed mainly in Russia. During the procedure, doctors used a special scalpel to score the surface of the cornea in order to reshape it. This type of surgery was most successful for mild cases of astigmatism and nearsightedness. Treating more severe cases sometimes resulted in fluctuating vision, a persistent glare, and starbursts.
Photorefractive keratectomy (PRK) is a procedure where, instead of sculpting the inner layers of the cornea, the surgeon uses the excimer laser to reshape the outer corneal surface. After removing the thin, protective epithelial layer of the cornea, the surgeon flattens, or steepens, the corneal curvature. The epithelial layer grows back, but conforms to the new shape of the cornea.
LASIK (laser-assisted in-situ keratomileusis) surgery is a proven procedure that is currently the gold standard for the surgical correction of nearsightedness. The entire surgery takes only ten to twenty minutes and the laser beam is generally used less than a minute. Numbing drops are first put into the eye and then the surgeon uses a delicate cutting tool called a microkeratome to cut a circular flap of tissue from the center of the cornea. This flap, still hinged to the cornea, is about the size and shape of a contact lens.
The surgeon folds this flap out of the way and uses a special laser to reshape the layers of the cornea underneath the flap – removing one microscopic layer at a time. A computer, reading a topographical map of the cornea, directs the laser beam to remove tissue where needed. The excimer or cool laser vaporizes tissue without causing heat damage; but rather, it breaks down the molecular bonds.
The light beam of energy is absorbed into the tissue through vaporization without harming the nearby lens, iris, retina, or other eye structures. In nearsightedness, the laser will trim away layers from the centre of the cornea to flatten its dome shape. In farsightedness, the laser will trim away a doughnut-shaped ring to produce a steeper curve.
With astigmatism, the laser will smooth out the distortion in the curvature of the cornea. After this brief sculpting, the surgeon returns the corneal flap to its position over the treated area and places a clear shield over the cornea, which will be worn overnight. The flap quickly reattaches itself to the cornea without stitches.
Complications of laser surgery include failure to achieve the intent, loss of central or peripheral vision, bleeding in the eye, early or late increase in pressure in the eye (glaucoma), corneal burns, damage to the lens (cataract), retinal hole, collection of fluid in the back of the eye, damage to the optic nerve, iris, or to intraocular lens implants, loss of vision or the eye.
Benefits and Disadvantages of Eye Surgery: Surgery allows about 70% of nearsighted people to achieve 20/20 vision without corrective lenses and more than 90% achieve at least 20/40 vision – the required minimum to pass an eye exam for a driver’s license in most places. More recent studies are showing that these percentages are on the rise with improved technology and surgical skills.
Functional vision returns in seven to ten days after PRK and one to two days after LASIK. Two months after surgery, the visual acuity of those who had the PRK procedure is about the same as for those who had LASIK. Once the numbing drops wear off, there may be a sandy sensation in the eye for a day or two.
LASIK is the less painful of the two because the exposed nerve endings of the cornea are covered by the corneal flap. With PRK, the pain can be more intense, lasting for several days and sometimes requiring powerful painkillers.
After LASIK surgery, about two percent of the patients do not see as clearly as they did before the procedure. That number drops to one percent with PRK surgery. Between five and fifteen percent eventually need a second surgery to further shape or enhance their vision.
Other problems that sometimes arise are: increased sensitivity to light; more problems with glare, cloudy vision – which typically disappears over time but may continue in some people; decreased night vision with halos around lights; and intolerance to contact lenses. The cost is around one to two thousand dollars per eye and not usually covered by insurance.