How LASIK works: Morris Eye Group San Diego
What Is Refraction?
When light reaches an angled surface it will bend. Convex surfaces bend light toward the center, and concave surfaces bend light away form the center. This phenomenon of bending light is called refraction. Your eye has many different angles that refract light to focus on the retina in the back of your eye.
In a perfect eye, the cornea refracts about 80% of light onto the crystalline lens. The crystalline lens then refracts about 20% onto the retina. If light does not refract onto the retina correctly, a person may suffer from near or far-sightedness. This problem is called a refractive error and can be corrected at Morris Eye Group through LASIK surgery or PRK surgery.
Some patients wonder how a laser can correct their vision. The primary function of the laser in LASIK eye surgery is to ablate or remove corneal tissue, thus altering the shape of the cornea, and changing the refraction of light as it passes through. In myopic patients, the curvature of the cornea is flattened. For hyperopic patients, the laser is used to steepen the curvature of the cornea. In essence, the laser is used to reshape the front surface of the cornea. To reach the stroma (the portion of the cornea that is shaped), the corneal epithelium must be removed (as in PRK) or a flap must be created (as in LASIK). A corneal flap can be created using a microkeratome.
In laser vision correction, the goal is to alter the shape of the cornea, so that light passing through is properly focused on the retina. An Excimer laser emits a cool, ultraviolet beam (193 nanometers long) that actually vaporizes tissue by breaking carbon-to-carbon bonds. Corneal tissue can removed with phenomenal precision without harming adjacent tissue. Excimer laser vaporization is technically termed photoablation.
The unmatched precision that can be achieved using the Excimer laser makes it the tool of choice for sensitive laser vision correction procedures such as LASIK eye surgery. Each pulse removes approximately 0.25 microns of tissue. This can be compared to slicing 1/200 of a human hair, 1/28 of a red blood cell, or 1/39 millionth of an inch – this is achieved in 4 billionths of a second. This accuracy allows the refractive surgeon to sculpt the cornea gently yet effectively, producing a cornea that properly focuses light onto the retina.
To learn about the laser used at Morris Eye Group and Custom LASIK contact our San Diego office.
Microkeratomes in LASIK Eye Surgery
Microkeratomes work in a fashion similar to that of a carpenter’s plane. All of the latest designs feature a suction ring, which is attached to the eye to keep the cornea firm. Microkeratome have a plate that flattens the cornea while an oscillating blade incises the flap at a predetermined depth. Stopping the blade at the appropriate point leaves a hinge.
. Some newer versions use high-speed gas motors that produce smoother flaps more consistently. Although it is believed that smoother flaps produce better results, this has not been proven in any scientific paper. Some microkeratome manufacturers are developing disposables. These may prove to be the wave of the future; however clinical experience with disposable microkeratomes has been limited. There have also been some ideas advanced regarding flap placement, but clinical experience has yet to prove these alternate techniques are superior.
