What Is Refractive Surgery?
The front of the eye is covered by a curved clear portion called the cornea which focuses light on the retina and allows us to see. In order to see the image crisply and clearly, the light has to be focused into a fine small dot. Unfortunately, as the eye grows and changes with age, the shape does not perfectly adapt to the change, and most people’s focal point looks more like an irregular smudge. Fortunately, wearing glasses or contact lenses helps refocus the light back into a point and gives us great vision. The eye typically stops making major changes in shape in our late teens.
Refractive surgery started with radial keratotomy (RK) in 1974, where nearsightedness and astigmatism were corrected by using a knife to make incisions in the cornea to change its shape. In 1987, it was discovered that a laser can be used to precisely change the shape of the cornea to effectively “polish” the glasses/contact lens prescription onto the eye. This first laser procedure became known as photorefractive keratomileusis (PRK). This allowed millions of people to become glasses-free and was found to be superior to the RK knife surgery. In 1992, laser in-situ keratomileusis (LASIK) was introduced in the USA for correction of vision by slightly modifying the PRK technique with an addition of a flap. In the early 2000’s, the intraocular collamer lens (ICL) received FDA approval for correction of nearsightedness where a secondary lens is implanted into the eye on top of the natural lens.
RK is surgery where radial incisions are made towards the center of the cornea to relax the contour and flatten the surface to reduce nearsightedness. After the results of the PERK conducted in the early 1990’s showing the incisions to be unstable long term, the procedure was abandoned and is no longer performed in the US. Arcuate incisions (AK), however, are made in the periphery away from the center and have shown long-term stability and efficacy to treat astigmatism and are currently in use.
PRK involves direct removal of the surface cells followed by application of the laser to reshape the eye. The cells are then allowed to grow back over a few days. Full healing takes several months but the procedure avoids any complications associated with a LASIK flap.
LASIK involves using a laser to create a partial thickness flap in the cornea which is then lifted out of the way and a second laser is used to reshape the eye underneath the flap. The flap is then gently laid back on the eye and allowed to re-adhere. Full healing and vision recovery are much faster compared to PRK, but there are new risks associated with the flap, such as epithelial ingrowth or flap dislocation.
ICL involves placing a plastic lens inside the eye (almost like a contact lens implant). The procedure also requires a small hole in the iris to prevent angle closure glaucoma in the future. The surgery avoids the risks associated with LASIK or PRK laser treatment, but carries the risks of intraocular eye surgery and possible cataract formation.
What is the goal of the surgery?
The goal of refractive laser surgery is to change the cornea to focus light without the need for glasses and contacts. This is done using a sophisticated optical engineering algorithm to calculate how many laser pulses and at which areas are needed to reshape the cornea for the individual to properly focus light. It cannot fix problems and restore vision lost due to glaucoma, macular degeneration, or irregular astigmatism.
How is the procedure performed?
The procedures are all performed on an outpatient basis and are typically performed on both eyes, using new sterile equipment for each eye. Relaxing medication is given prior to the procedure, therefore a driver is required for home transportation. A small device is used to keep the eye open during the procedure and a camera is used to track the eye movements to ensure the laser pulses are delivered at the right spots. The vision is usually quite functional by the next day, but takes several weeks to months to reach full effect (depending on the procedure).