LASIK/PRK (Laser Refractive Surgery)
Understanding Refractive Surgery
Refractive errors of the eye (myopia, hyperopia and astigmatism) are caused by an imbalance in the light-bending power of the cornea (the window of the eye) and the natural lens inside the eye with respect to the length of the globe (the eyeball). When light is focused either too strongly (near-sightedness or myopia) or weakly (far-sightedness or hyperopia), a clear image cannot fall upon the retina located on the inside back wall of the eye. The retina is the nervous tissue that transforms light energy into neural signals, and when the retina receives an unfocused image, it must send signals of an unfocused picture to the brain. The retina is much like the film in a camera; a healthy retina receiving poorly focused images is about as useless as a camera with expensive film but an out-of-focus lens; both provide only poor quality images. In recent years, our understanding of the optical properties of the cornea and dramatic improvements in lasers have permitted the development of painless procedures lasting only minutes and designed to successfully reshape the cornea. This improves its natural abilities to focus light onto the retina without additional help from spectacles or contact lenses.
Who Might Benefit from Refractive Surgery
Patients with refractive error (myopia, hyperopia and astigmatism) who want less dependence on spectacles and contact lenses may be good candidates for laser refractive surgery. A stable glasses or contact lens prescription is one of the most important predictors of success in LASIK or PRK. In addition, special testing performed during a refractive surgery screening is necessary to confirm whether a patient is a good candidate for this type of procedure.
Photorefractive keratectomy, or PRK, is a procedure that reshapes the cornea by changing its front surface with a laser. In this procedure, the corneal epithelium (layer of skin cells) is removed either chemically or mechanically, and a special laser called an excimer laser (VISX) ablates (vaporizes) the front of the stroma (the thickest and strongest layer of the cornea) until it reaches a desired, pre-calculated thickness and shape. The procedure is bloodless and performed in the office using numbing drops for anesthesia. Contact lenses are placed on the operative eyes to serve as “bandages” and help keep the patient comfortable while the corneal epithelial cells heal back into place on the surface of the reshaped cornea. This healing process using takes 3-4 days to reach completion. Although the quality of vision after PRK and LASIK is equivalent by 3 months after surgery, recovery to clear vision is slower after PRK relative to LASIK. Although patients can expect to be functional with most daily activities by 3-4 days after surgery, visually demanding tasks such as driving at night, driving in bad weather, or reading fine print may be difficult for the first month after PRK. The major benefit of PRK, though, is that the structural integrity of the eye is maintained. Therefore for anyone at risk of facial trauma after laser refractive surgery (athletes, military, police, and firemen), PRK is usually the laser procedure of choice.
LASIK is an acronym for Laser Assisted In-Situ Keratomileusis, a procedure for improving vision in individuals with myopia, hyperopia or astigmatism by ablating a portion of the corneal stroma, the thick, strong central layer of the cornea, without removing the corneal epithelium. During LASIK, 2 different lasers are used. One called a femtosecond laser (Intralase) is used to cut a thin layer of corneal tissue called a flap. This flap is then lifted, and the second laser called an excimer laser (VISX), is used to thin and reshape the cornea. After the reshaping is complete, the flap is carefully slid back into position. The recovery period for this procedure is shorter and more comfortable relative to PRK. As a matter of fact, the quick visual recovery after LASIK is the primary reason why this procedure is most popular and most commonly promoted in the US. The major long term disadvantage of LASIK relates to the flap. Even though healing does take place after the LASIK flap is repositioned, the flap permanently weakens the cornea to withstand an abrasive force. That means there are rare case reports of patients even years after LASIK who sustained a scratch or hit to the eye that caused the flap to shift or wrinkle. If this trauma is dealt with quickly by an ophthalmologist, the flap can usually be repositioned successfully, but long term wrinkles called striae or other problems can permanently distort or blur the vision. It is reassuring to know that these problems occurred more frequently in the past when the flap was created using a blade called a microkeratome. Since the surgeons at Eye Doctors of Lancaster use a laser (Intralase) for flap creation with all-laser LASIK, these complications are more rare.
Intraocular Collamer Lenses (ICLs)
Intraocular collamer lenses (ICLs) are similar to soft contact lenses but are designed to be implanted in your eye rather than placed on the surface of the cornea. These are designed to correct your refractive error without removing any normal corneal tissue which occurs in LASIK or PRK. However, since implantation of an ICL is intraocular surgery, there are potentially more risks associated with ICLs than with normal contact lenses, LASIK or PRK. This procedure is usually reserved for patients with high refractive errors or those who are not good candidates for LASIK or PRK as determined by special testing performed during a refractive surgery screening appointment.
Radial keratotomy, or RK, is a procedure where a microsurgery blade is used to cut radial or circumferential cuts into the cornea, which causes the peripheral cornea to bow or steepen and the central cornea, where most light is focused, to flatten. This procedure is no longer performed, but was popular in the late 20th century for patients with near-sightedness (myopia) and astigmatism. The main reason this procedure is no longer performed is that the long term results are less stable than LASIK or PRK, and patients who had RK tend to drift into far-sightedness (hyperopia) over time. In addition, many patients after RK experience fluctuating vision through the day as the intraocular pressure naturally changes in a cyclic (diurnal) pattern.