System Of Precise Predictable Keratorefractive Surgery
American ophthalmologists refined RK and developed newer instruments and techniques to improve results. This refined procedure, called the system of precise predictable keratorefractive surgery, is the standard for this type of surgery. Prospective RK patients must have healthy corneas and be deemed suitable candidates after a presurgical examination of the eye. The surgeon measures the curvature of the cornea in order to obtain a baseline from which to determine the amount of flattening that is required. Therefore, patients who wear hard contact lenses must remove them for three weeks before their preoperative eye examination, because the lenses can mold the cornea and change its natural curvature. Patients who wear soft lenses must remove them at least three days before the exam.
On the day of the examination, patients are generally given a sedative to help them relax during the operation, but the surgery itself is painless, and is not done under anesthesia. While on the operating table, the area around the patient's eye is cleaned, and topical anesthetic drops are administered to the eye.
The surgeon places an ultrasound probe over the eye to measure the thickness of the cornea in several spots. This measurement is critical, because each incision must penetrate to at least 75% of the depth of the cornea, which is about 0.02 in (0.5 mm) deep, in order to obtain the greatest flattening effect without penetrating the vitreous fluid underneath.
A diamond blade secured within a slot on the handle of the cutting instrument is then adjusted to within a hundredth of a millimeter of the thinnest spot on the cornea. The surgeon then places dark lines on the cornea to guide the blade. Under high magnification with an operating microscope, the surgeon pushes the blade into the cornea with enough force to produce a slight indentation. With the blade adjusted to prevent it from being inserted too deeply, the surgeon then makes a number of incisions in the cornea which radiate from the pupil like the spokes of a wheel, leaving a central clear zone. The patient wears a patch after the operation, and recovery takes about one to two days. When RK is to be done on both eyes, they are operated on during separate visits at least several months apart.