Refractive Surgery – Introduction
When we speak of “refractive surgery”, we mean surgery to correct the common refractive disorders: myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. Many of the terms used in this discussion of refractive surgery depend on an understanding of the eye.
The basis for nearly all kinds of refractive surgery is the reshaping of the cornea. Myopia is corrected by making the cornea flatter, hyperopia is corrected by making the cornea more curved, and astigmatism is corrected by making the cornea more perfectly round (i.e. less oblong).
The Excimer Laser
The excimer laser produces a beam of ultraviolet light, which means that its wavelength is somewhat shorter than that of visible light. More specifically, the wavelength of the ArF laser is 193 nm (19.30 millionths of a centimetre or about 7.6 millionths of an inch). This wavelength is uniquely suited to the task of corneal surgery. When this light meets corneal tissue, molecular bonds are broken and a microscopic layer of tissue is removed with no thermal (heat) damage to the remaining tissue. This allows the cornea to be sculpted gently and precisely.
Photorefractive keratectomy (PRK) is a procedure in which the front surface of the cornea is directly sculpted into a more desirable shape by an excimer laser after the surgeon removes the thin outer “skin” (the epithelium).
A soft contact lens is then placed on the patient’s eye to protect the cornea while it heals. The epithelium grows back, typically in three or four days, after which the protective contact lens is removed.
Laser-assisted intrastromal keratoplasty (LASIK) is a procedure in which a specialized blade called a keratome creates a flap of corneal tissue which is then lifted away from the rest of the cornea (to which it remains attached by a “hinge”). The underlying corneal bed is sculpted by an excimer laser, and then the flap is secured in its original position.
Each of these two procedures has its respective advantages and disadvantages. SmartSurf PRK is the more versatile procedure in the sense that it is effective for a wider range of patients. If you come to us for refractive surgery, we will help you decide which treatment is best for you. In general, we feel that SmartSurf PRK is appropriate for all levels of myopia, and for all cases of hyperopia.