The concept of surgically correcting vision was first recorded in the 1800s with the use of a spring-mounted mallet to flatten the cornea. Fortunately, laser eye surgery methods have progressed significantly since then, propelled further with the invention of tools such as the femtosecond and excimer lasers.
Refractive error, also known as ametropia, refers to a mismatch of the power of the eye’s focusing system (the cornea and the lens) to the length of the eyeball, also known as the axial length. As light passes through the cornea and lens of the eye, ideally it is focused, or refracted, to a sharp point on the sensory retina at the back of the eyeball – this is what we perceive as clear vision. In eyes where light comes to a focus either before the retina (as is the case of short-sightedness or myopia), behind the retina (as in long-sightedness or hyperopia), or at two separate points around the retina (as in astigmatism), vision is blurry and the patient is considered to have a refractive error.
The use of glasses and contact lenses helps to refocus the light entering the eye so that it will come to a clear point on the retina. However, these optical aids come with some disadvantages, such as life-long costs, cosmetic issues, and even some eye health risks. For patients seeking freedom from the inconvenience of glasses and contacts, laser eye surgery could be a very tempting option. So, how does laser eye surgery work?
How Does Laser Eye Surgery Work?
Laser eye surgery aims to adjust the focusing power of the eye through surgical means, essentially by reshaping the cornea. In addition to the refractive power of the lens inside the eye, the shape of the cornea is responsible for a proportion of the refraction of incoming light.
Details of how laser eye surgery works will be dependent on the specific technique used. We have a growing armamentarium of laser eye surgery methods which continue to expand the criteria of suitability, allowing more and more patients access to laser vision correction where perhaps just a decade ago they may have been deemed ineligible.
Despite being one of the earlier methods, PRK continues to be a valuable technique still used today. As the excimer laser is applied to the inner corneal layers known as the stroma for the reshaping process, the superficial layer of corneal cells called the epithelium must first be removed. The removal of epithelium is performed either with an alcohol solution or manually with a hand-held instrument, which then exposes the corneal stroma. Guided by computer, the excimer laser then removes select areas of the cornea to adjust its shape, a process called photoablation. After the operation, the cornea naturally regenerates its epithelial layers as part of the healing process.
Laser-Assisted in Situ Keratomileusis
Probably one of the most well-known laser eye surgery techniques, LASIK is similar to PRK in that it requires the corneal epithelium to be moved away in order for the excimer laser to access the underlying stromal layers for reshaping. However, unlike PRK, the LASIK method creates a flap of superficial corneal tissue which remains attached to the eye by a hinge. The flap may be formed using a manual bladed instrument or with another type of laser tool known as a femtosecond laser. Once the photoablation reshaping process is complete, the corneal flap is replaced over the eye and allowed to self-seal. A benefit of LASIK surgery is the shorter recovery time compared to PRK; however, one disadvantage is that LASIK is not suitable for thinner corneas as the creation of the flap reduces the amount of corneal tissue available for reshaping.
Small Incision Lenticule Extraction
SMILE® laser eye surgery is a much more recent method and is not yet widely offered across all ophthalmology practices in Australia. Hailed as a revolutionary, minimally invasive refractive surgery technique, SMILE® allows the biomechanical stability of the cornea to remain largely intact, resulting in faster healing times and a lower risk of complications. Unlike both PRK and LASIK, the epithelium is more or less undisturbed, and the corneal stroma is instead accessed via a small keyhole incision. A femtosecond laser is used to create a disc-shaped sliver of tissue within the stroma known as a lenticule, the dimensions of which are pre-calculated to correct for that eye’s particular refractive error. This lenticule is then removed through the keyhole incision, adjusting the cornea’s overall shape and curvature and thereby redirecting light to focus clearly onto the retina.
So, there you have it – how laser eye surgery works. There are also other forms of refractive surgery that don’t depend on the use of laser technology; some of these techniques may be more suitable for certain patients, particularly those who have factors that make any sort of corneal disruption undesirable or those who have insufficient corneal thickness for reshaping.
Surgical procedures such as intraocular contact lenses (ICL) and refractive lens exchange (RLE) still achieve clear vision with independence from optical aids but without any significant interference to the cornea.
Patients who have been excluded from laser refractive procedures based on inadequate corneal thickness may find themselves eligible for refractive surgery through one of these other techniques.
The idea of surgery on such a delicate, sensitive organ as the eye can be daunting, but refractive surgery in Australia is associated with very high rates of success.
To discuss your eligibility for surgical vision correction, call us on (03) 9070 5753 and make an appointment with our rooms today.
Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.