Pre-Surgery Requirements Patients wearing soft contact lenses typically are instructed to stop wearing them approximately 7 to 10 days before surgery. Some surgeons recommend that patients wearing hard contact lenses should stop wearing them for a minimum of six weeks plus another six weeks for every three years the hard contacts had been worn. Before the surgery, the surfaces of the patient's corneas are examined with a computer-controlled scanning device to determine their exact shape. Using low-power lasers, it creates a topographic map of the cornea. This process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and locations of corneal tissue to be removed during the operation. The patient typically is prescribed an antibiotic to start taking beforehand, to minimize the risk of infection after the procedure. Higher order Aberrations are visual problems not captured in a traditional eye exam. In a young healthy eye, the level of higher order aberrations are typically low and insignificant. Concern has long plagued the tendency of refractive surgeries to induce higher order aberration not correctible by traditional contacts or glasses. The advancement of lasik technique and technologies has helped eliminate the risk of clinically significant visual impairment after the surgery. There has been controversy about the amount of higher order aberrations that would lead to significant vision impairment. In extreme cases, where proper policy was not followed and before key advances, some people could suffer rather debilitating symptoms including serious loss of contrast sensitivity in poor lighting situations. Over time, most of the attention has been focused on spherical aberration. Lasik and PRK tend to induce spherical aberration, because of the tendency of the laser to undercorrect as it moves outward from the center of the treatment zone. This is really only a significant issue for large corrections. There is some thought if the lasers were simply programmed to adjust for this tendency, no significant spherical aberration would be induced. Hence, in eyes with little existing higher order aberrations, "wavefront optimized" lasik rather than wavefront guided Lasik may well be the future. Regardless, most patients with even the highest corrections remain highly satisfied even with conventional lasik. Possible Complications The incidence of flap complications has been estimated to be 0.244%. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience. A slipped flap (a corneal flap that detaches from the rest of the cornea) is one of the most common complications. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep, to let the flap heal. Flap interface particles are another finding whose clinical significance is undetermined. A Finnish study found that particles of various sizes and reflectivity were clinically visible in 38.7% of eyes examined via slit lamp biomicroscopy, but apparent in 100% of eyes using confocal microscopy.
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