Refractive Surgery and Orthokeratology
Refractive Surgery is an exciting development in the treatment of nearsightedness and astigmatism. It provides a viable alternative to spectacle or contact lens wear. Several treatment modalities are currently being studied for farsightedness but none have proven to be highly reliable at this time. We will discuss some of the various forms of refractive surgery being performed in the United States today.
The basic concept for all refractive surgery procedures involves altering the shape and power of the cornea. The cornea is the “window” of the eye that accounts for nearly 70 percent of the eye’s focusing power. By altering the shape of the cornea, the prescription of the eye can be changed.
While optometrists are not licensed to perform surgery, they can in most instances participate in patient care by performing pre- and post-operative examinations.
Radial Keratotomy (RK)
Radial Keratotomy is a surgical procedure in which a surgeon flattens the cornea by placing a series of radial incisions into the cornea. These incisions cause the cornea to flatten thus creating a power change. This procedure can correct nearsightedness between 1.50 and 6.00 diopters.
Photorefractive Keratectomy (PRK)
Photorefractive Keratectomy is a laser surgical procedure which uses the excimer laser. The physician applies the laser to the corneal surface and altering its shape. This procedure will correct nearsightedness between 1.50 and 6.00 diopters. The amount of corneal shaping is calculated and controlled using computer technology.
Automated Lamella Keratectomy (ALK)
Automated Lamellar Keratectomy is a surgical technique used to treat very high amounts of nearsightedness. It is typically reserved for nearsightedness greater than 6.00 diopters. This surgical technique involves removing the top portion of the cornea called the corneal cap with an instrument called a micro-keratome. Once the cap is removed, a small layer of corneal tissue is shaved off with a second application of the micro-keratome. The corneal cap is then placed back in position and allowed to adhere back to the eye. This produces a thinning of the cornea and a reduction in the amount of nearsightedness.
This procedure is not available for astigmatism correction.
Laser In-Situ Keratomelieusis (LASIK)
Laser in-situ keratomelieusis is a surgical technique that combines the micro-keratome used in ALK and the excimer laser used in PRK. This procedure allows the surgeon to correct a wide range of nearsightedness. During the surgical procedure the micro-keratome is used to slice the front portion of the cornea and to expose the area that will be treated with the laser. Unlike ALK, the corneal cap is not completely removed but a “flap” is created.
Once the flap is created and folded back, the PRK laser is applied to the exposed area. The laser will cause corneal tissue ablation or tissue reduction which creates a thinner cornea thus reducing the amount of nearsightedness.
When the laser is finished, the corneal flap is gently put back in place. This increasingly popular surgical procedure is being studied at centers across the country to determine its safety, predictability and long term prognosis.
This procedure seems to be the most encouraging in the attempts to correct farsightedness.
Orthokeratology is a nonsurgical procedure used to flatten the cornea and reduce nearsightedness. This procedure involves fitting a series of contact lenses over an extended period of time with each lens creating a slightly flatter corneal shape thus reducing the amount of nearsightedness. This procedure does not provide a permanent correction but requires contact lenses to be worn on a scheduled basis to retain the effects of nearsighted reduction.