The eye is like a camera. To see clearly, images must travel through the eye and be focused on the retina, in the back part of the eye. The cornea and the lens are responsible for refracting (bending) light to help focus it on the retina. Out of the two, cornea accounts for the major part of light bending.
Unfortunately, few eyes with a refractive error cannot perfectly focus the image onto the retina without the assistance of either glasses or contact lenses. Patients who are myopic (nearsighted) are able to see well up close without glasses, but require glasses for distance.
Patients who are hyperopic (farsighted) are able to see somewhat clearly at distance, but not well up close. Some farsighted people cannot see well up close or at a distance.
Finally, patients with astigmatism have different power in different meridians which prevents the image on the retina from being in focus.
Lasik stands for Laser-Assisted In-Situ Keratomileusis. It is now one of the most popular choices for refractive eye surgery, and boasts one of the highest patient-satisfaction rates among medical procedures. Lasik involves the use of a laser to permanently change the shape of the cornea, the clear covering of the front of the eye. With the availability of advanced Lasik machines using Wave Front Technology, customized and very precise ablation is possible. Lasik is a quick and often painless procedure, and for the majority of people, the surgery improves vision and reduces the need for corrective eyewear.
During the Lasik procedure femtosecond laser or a microkeratome (hand-held blade) is used to create a precise partial-thickness hinged flap on the eye. This flap is only 110 to 160 microns thick "approximately one-tenth of a millimeter. Once the flap is created, the surgeon lifts it to expose the underlying corneal tissue. A laser, which you cannot see or feel, is then applied, typically for a few seconds. The time duration depends on the frequency of the machine. Finally, the surgeon finishes the procedure by repositioning the flap back on the cornea. The entire surgery lasts between 5-10 minutes for both eyes.
Lasik is performed under topical anesthetic (eye drops) to numb the eye. Patisnts usually do not experience any pain during the procedure. When the vacuum ring is applied during the procedure, the patient experiences a sensation of pressure and then his or her vision fades for a few seconds. The microkeratome - the instrument the surgeon uses to create the flap - and the laser do not cause any pain or discomfort. For several hours after the procedure, many patients describe a mild burning sensation and discomfort. Therefore, taking a nap for the first 2 to 3 hours after Lasik is advisable. This discomfort usually disappears after the first few hours.
There are multiple other laser-assisted vision correction surgeries. Some of the common ones include photorefractive keratectomy (PRK) and Epi-Lasik. PRK was the forerunner of Lasik, and is a similar laser surgery but without the corneal flap. PRK and Epi-Lasik have the advantage of being possible in those cases where Lasik cannot be performed due to thinner or borderline corneas. In both these techniques only the superficial corneal layer called the epithelium is removed and the bed is exposed to the laser. The superficial layer grows back within a few days.