By David Ivanov, Biochemistry and Molecular Biology, 2015
LASIK, or laser-assisted in situ keratomileusis, is a surgical procedure commonly used to correct for visual defects or lack of visual clarity. Commonly referred to as laser eye surgery, LASIK is a type of surgery that is used to alleviate visual loss associated with common defects of the eye, such as myopia (nearsightedness), hypermetropia (farsightedness), and astigmatism. Astigmatism, like near and far-sightedness, can be caused by the irregularity in shape of the cornea that leads to blurred vision. For all three cases, corneal remodeling via LASIK can be performed (Thomson, 2015).
The cornea is the outermost layer of the eye, the transparent part that one can touch, and upon which contact lenses are placed. It is responsible for most of the focusing power, and thus is a common culprit in visual defects of the eye. The cornea focuses the light reflected into the eye, through the lens and onto the the retina at the back of the eye, which senses light and converts it to nerve impulses, and transmits the resulting image to the brain for processing. This then produces the image that we ‘see’. While the retina is the part of the eye that is light-sensitive and is responsible for transmitting the image to the brain, the cornea, along with the lens, must focus light reflecting off of three dimensional surfaces so that they strike onto the anterior, or front part of the retina. Without this precise focusing of light rays directly onto the retina, the brain generates a blurred image (NKCF 2014).
Image courtesy of CCT
The shape of the cornea is of vital importance to the eye’s ability to bend incoming light rays in a manner that will focus the rays onto the retina. While the shape of the lens behind the cornea can be adjusted to assist with focusing, the cornea has a fixed shape. Therefore, anomalies in its shape can cause loss of visual acuity, or sharpness. For instance, a cornea that is too thick can cause the light rays to focus on a point in front of the retina, which leads to blurred vision, especially with objects far from the eye. This is common in the case of nearsightedness. The cornea can also be, among other things, too flat, causing the light rays to focus behind the retina. This leads to blurred vision from objects at a distance, a symptom of farsightedness. While near and far-sightedness can be caused by other more complex irregularities in the eye, visual defects associated with the abnormal shape of the cornea can be corrected for with external lenses, as in glasses or contacts. Another option is to permanently alter the shape of the cornea to allow light to focus properly onto the retina and produce a clear image (NEI).
While LASIK isn’t the only surgical procedure to adjust the shape of the cornea, it is the most popular. In fact, it is the most common elective, or non-emergency, surgery in North America (TLC 2015). Although the idea of having an ultraviolet laser beam pointed directly, and intentionally, into one’s eye while conscious and lucid can be a scary prospect, LASIK is considered to be very safe and highly effective. The procedure can be done in less than thirty minutes for both eyes and is performed in an outpatient, or non-hospital, setting (Wachler 2015). The procedure itself is relatively simple as far as surgeries go. It begins with anesthetic eye drops that numb the surface of the eye. Once moistened, a suction ring is applied to keep the eye stationary. The ophthalmologist, a surgeon specialized in treating conditions of the eye, can then ‘make the cut’ (FTC 2012).
The cornea, while transparent, actually consists of several layers of tissue. In order to remold the cornea, the ophthalmologist must first get past the tough outer layer of the eye. Since the cornea is the part of the eye that is exposed to the outside world, it must have a protective function to prevent damage to, or infection of, the eye (Garrity 2013). To access the inner layer of the cornea that can be reshaped for vision correction, the surgeon first creates a flap in the outer layers of the cornea. This is done by either a microkeratome, small, special blade designed to cut corneal flaps, or a high-energy laser. The cut is made so that a part of the outer layer of cornea is intact, creating a sort of hinge, which allows the ophthalmologist to lift the flap of cornea and access the inner layers. A laser is then used to remove a microscopic amount of tissue in order to properly shape the cornea. The flap is then placed back down, and a shield, typically of a clear plastic, is temporarily placed over the eye to keep the flap in place. No stitches are used and the cornea essentially heals on its own (FTC 2012).
Of course, no surgery is without complications, and LASIK is no exception. While it is heralded as extremely safe, the procedure is irreversible and can, in rare cases, lead to a permanently damaged cornea due to improper healing or infection post-operation. As one might perhaps expect, blindness or other vision loss may occur as well. While most people achieve 20/20 vision (sometimes erroneously referred to as ‘perfect vision’), some detailed vision may be mildly impaired. Patients do not gain superhuman vision, and will likely need reading glasses in their forties. More than ten percent will have their improved vision deteriorate to the point of requiring retreatment (FTC 2012). However, considering its very high success rate and low risk of complications, LASIK remains a safe and viable treatment for nearsightedness, farsightedness, and astigmatism, and has been FDA approved since 1998 (ES).
Thompson, V. LASIK Laser Eye Surgery: A Complete Consumer Guide. March, 2015. Available from: http://www.allaboutvision.com/visionsurgery/ (Accessed April 2015).[NKCF] How Does The Human Eye Work? January 2014. Available from: https://www.nkcf.org/how-the-human-eye-works/ (Accessed April 2015). [CCT] What is a Cornea Specialist? 2013. Cornea Consultants of Texas [Image] Available from: http://www.corneaconsultantstx.com/show.php?page=forpatients_whatisacorneaspecialist [NEI] Refractive Errors. National Eye Institute. Available from: https://www.nei.nih.gov/health/errors (Accessed April 2015). [TLC] Types of LASIK Eye Surgery. TLC Laser Eye Centers. 2015. Available from: https://www.nei.nih.gov/health/errors (Accessed April 2015).
Wachler, B. LASIK Risks and Complications. March, 2015. Available from: http://www.allaboutvision.com/visionsurgery/lasik_complication_1.htm (Accessed April 2015).
[FTC] The Basics of Laser Eye Surgery. Federal Trade Commission. Consumer Information. August 2012. Available from: https://www.consumer.ftc.gov/articles/0062-basics-lasik-eye-surgery#risks (Accessed April 2015).
Garrity, J. Protective Features of the Eyes. Merck Manual. October, 2013. Available from: http://www.merckmanuals.com/home/eye-disorders/biology-of-the-eyes/protective-features-of-the-eyes (Accessed April 2015).
[ES] LASIK – Laser Eye Surgery. Eye Smart. American Academy of Ophthalmology. Available from: http://www.geteyesmart.org/eyesmart/glasses-contacts-lasik/lasik.cfm (Accessed April 2015).