To fully understand how refractive surgery works, you need to understand how your eye works. This basic knowledge will help you determine if LASIK is right for you. The primary purpose of your eye is to focus light onto the retina. When the rays of light are not focused properly, images may be blurred or distorted and you need glasses or contact lenses to correct it.
Your eye works very much like a camera. Light enters the eye through the cornea, the clear front surface or “window” of the eye. As the light passes through the cornea, it is bent or refracted. This bent light then travels through the pupil and into the lens. The lens acts to focus the light so that it concentrates perfectly on the retina. The retina turns the light energy into electrical impulses that travel along the optic nerve from the eye to the brain, where the image is interpreted.
If you have a refractive error, then the light is not focusing on the retina in the back of your eye properly. In order to fix this problem and improve your vision, you can choose to have refractive surgery. Refractive surgery is a common procedure that uses a laser to reshape your cornea so that light refracts onto your retina correctly. The light that may have focused too far in front or behind your retina before laser surgery, can now focus directly on it giving you much clearer vision. Although refractive surgery cannot guarantee 20/20 vision, it can significantly improve the eyesight of most people.
Many patients ask, “Why use a laser?” What the laser does is reshape the center of the cornea to flatten its curvature in the case of myopia or nearsightedness. In the case of farsightedness, tissue is reshaped in the periphery of the cornea to steepen its curvature.
The laser essentially reshapes the cornea’s front surface. To do this, the corneal stroma (the tissue beneath the corneal epithelium, the outmost layer) must be exposed. This can be accomplished by removing the corneal epithelium with a laser (a procedure known as PRK) or by creating a corneal flap with a microderatome (performed in LASIK).
Many types of lasers are used in eye surgery. Argon lasers heat tissue and have been used for years to treat disorders such as diabetic retinopathy and glaucoma. YAG lasers break tissue bonds by creating a shock wave and are used following cataract surgery and to treat certain types of glaucoma. The Excimer laser is a gentle laser uniquely suited to the task of refractive corneal surgery.
The Excimer laser produces a cooler, ultraviolet beam of light (193 nanometers in length) that vaporizes tissue as it breaks carbon-to-carbon bonds without the effect of harming any adjacent tissue. This means that the tissue can be removed in a precise fashion on a microscopic level. This process is called photoablation.
The unparalleled precision of the Excimer laser makes it uniquely suited to the task of refractive corneal surgery. Each pulse of the laser removes 0.25 microns of tissues. Think of it as slicing 1/200 of the diameter of a human hair in 4 billionths of a second. This allows the surgeon to literally sculpt the cornea into a more effective shape gently and precisely, which allows light to focus properly on the retina.
LASIK
Laser in-situ keramtomileusis, or LASIK, is the most commonly performed type of laser surgery. It is generally a safe and effective treatment for a wide range of common vision problems. Specifically, LASIK involves the use of a laser to permanently change the shape of the cornea, the surface layer of the eye.
LASIK is a quick and often painless procedure. For the majority of patients, the surgery improves vision and eliminates the need for corrective eyewear. However, as LASIK is a surgical procedure conducted on a delicate part of the eye, it is crucial that patients are well educated on the benefits and risks of the procedure, understand the importance of a thorough screening, and maintain realistic expectations about the procedure’s outcome.
Laser Assisted In-situ Keratomelusis (LASIK) begins with making a thin flap on the surface of the cornea. Next, the flap is gently lifted and the excimer laser is used to reshape the cornea by removing a thin layer of tissue from the center of the cornea stroma. The flap is then repositioned to complete the procedure. LASIK is performed on a wide range of refractive errors including farsightedness, nearsightedness, and astigmatism.
PRK
Photorefractive Keratectomy (PRK) involves using the excimer laser to remove a very thin amount of tissue from the surface of the cornea. This slight change in shape is all that is required to compensate for most focus problems. Currently, the excimer laser can be used to treat nearsightedness, astigmatism, and nearsightedness with astigmatism. The FDA has not yet approved PRK for use on farsightedness.
What is LASEK with an “E”?
Laser Epithelial Keratomileusis (LASEK) is a procedure that integrates the mechanics of LASIK (Laser Assisted In- Situ Keratomelusis) with the techniques of PRK.
Laser Epithelial Keratomileusis (LASEK) is similar to LASIK, but differentiated by the flap created during surgery. In a LASEK procedure, the surgeon temporarily removes only the epithelium (top layer of the cornea), instead of the epithelium and part of the deeper stroma layer, as done when creating a traditional LASIK flap. The excimer laser is then applied to the surface of the cornea in the same manner as PRK. LASEK can be thought of as a better alternative for patients with a thinner cornea.
Collagen Cross-linking
Collagen Cross-linking is a procedure that involves using an ultraviolet light to strengthen the chemical bonds in the corneal tissue where it is thinning and weakening, a condition commonly referred to as keratoconus. Though used around the world, it is still in the FDA approval process and is labeled as an experimental procedure.
Whether or not you are a candidate for PRK, LASIK, or LASEK, depends on your current prescription, cornea thickness and other individual eye characteristics, and overall eye health and history.
Which procedure is best, will be determined, following the comprehensive eye exam, however general guidelines do exist for all surgery candidates.
• Are over 21 years of age and have had a stable glasses or contact lens prescription for at least two years.
• Have sufficient corneal thickness (the cornea is the transparent front part of the eye). A LASIK patient should have a cornea that is thick enough to allow the surgeon to safely create a clean corneal flat of appropriate depth. (Thin corneas may sometimes be PRK or LASEK candidates)
• Are affected by one of the common types of vision problems or refractive error – myopia (nearsightedness), astigmatism (blurred vision caused by an irregular shaped cornea), hyperopia (farsightedness), or a combination thereof (e.g., myopia with astigmatism).
• Do not suffer from any disease, vision-related or otherwise, that may reduce the effectiveness of the surgery or the patient’s ability to heal properly and quickly. Discuss any concerns during your initial consultation.
• Are adequately informed about the benefits and risks of the procedure. Candidates should thoroughly discuss the procedure with their physicians.
