Laser eye surgery treatments, such as LASIK, have been a great medical advancement for those of us with imperfect sight. Though glasses and contact lenses do have their own advantages, laser eye surgery can overcome a lot of their drawbacks – situations like foggy or dirty lenses with glasses, increased risk of eye infections with contacts, constant cleaning and repairs or replacements become an issue of the past. However, though laser eye surgery is not an uncommon term amongst the bespectacled, what does laser eye surgery do, actually? Keep reading to find out how these ingenious treatments work.
How Refractive Error Works?
Refractive error is the umbrella term for the eye conditions we know as nearsightedness (myopia), farsightedness (hyperopia), astigmatism (uneven curvature of the cornea or lens), and presbyopia (the age-related decline of near focusing ability).
In the case of myopia and hyperopia, these errors arise from a mismatch between the focusing power of the cornea or lens at the front of the eyeball to the whole length of the eyeball, known as the axial length. In hyperopic eyes, the eyeball is too short for its focal length, meaning incoming light is focused behind the retina. We need light to come to a sharp point right on the retina for clear vision. In myopic eyes, the axial length is too long, so light comes to a focus too early.
While the crystalline lens of the eye is one refractive component of the eye, the cornea holds about two-thirds of the optical power. This is the clear dome covering your coloured iris. Understanding the role that the cornea plays underlies understanding what does laser eye surgery do and how it works.
What Does Laser Eye Surgery Do?
Put simply, laser eye surgery aims to reduce or eliminate the need to depend on optical aids such as glasses and contact lenses. And as alluded to earlier, it does this by focusing on the power of the cornea.
The curvature and shape of the cornea determine its refractive power. The more curved it is, the higher its refractive power. Conversely, flatter corneas have a lower refractive power, which equates to a longer focal length. The longer the axial length of an eyeball, such as in myopia, the lower the refractive power of the eye needs to be to get that clear focus on the retina.
Laser eye surgery is based on reshaping the cornea and altering its curvature. By doing this, it can change its refractive power to accommodate a long (myopic) or short (hyperopic) eye. Laser eye surgery can even be used to fix astigmatism and presbyopia.
Types of Laser Eye Surgery
There are several variations of laser eye surgery, all with their pros and cons, however, all are based on the same premise of reshaping the cornea to correct refractive error. Here are some of the more common ones.
LASIK
LASIK stands for laser-assisted in situ keratomileusis. This popular procedure involves creating a flap of superficial corneal tissue. This flap is kept attached to the rest of the cornea but during the surgery is moved to the side. By moving aside the uppermost layers, the surgeon is able to use an excimer laser to remove precise sections of deeper corneal tissue in a process known as photoablation. Photoablation is essentially using the laser to vaporise select areas of tissue. Once the cornea has been reshaped, the flap is put back in place and usually allowed to self-seal without stitches.
PRK
Photorefractive keratectomy is an older method of laser eye surgery but is still often used today. As there are eyes that are unsuitable for LASIK, PRK is able to provide access to refractive surgery for more people so is still considered a valuable and safe technique.
During PRK, the top layer of corneal tissue known as the epithelium is removed entirely. This can either be done with a chemical solution or with a handheld instrument. Removing the epithelium clears the way for the excimer laser tool to perform photoablation on the deeper corneal layers in the same way as is done in LASIK. After the procedure is complete, the corneal epithelium regenerates on its own.
SMILE
SMILE surgery is one of the newest laser vision surgery techniques. It stands for small incision lenticule extraction, a descriptive name for this minimally invasive technique. During a SMILE procedure, a precisely shaped disc, or lenticule, of deeper corneal tissue is created using the laser tool. This is performed without needing to disturb the outer layers of the cornea, hence the minimally invasive nature of this technique. A keyhole incision is cut near the edge of the cornea, through which the lenticule can be removed from the eye. This results in the cornea being reshaped from within with minimal disruption to its biomechanical stability.
Having different types of laser vision correction techniques has widened the eligibility criteria for more people to be able to access refractive surgery. However, there are still factors that may make someone unsuitable for any type of laser sight correction. These include very high prescriptions, vision loss from other conditions, or corneal disease. However, some people who are ineligible for laser eye surgery may still be considered for non-laser refractive methods such as refractive lens exchange or implantable Collamer lenses.
If you’re interested in pursuing laser sight correction or have more questions about what does laser eye surgery do, how it works, and whether it might be right for you, speak to your eye care professional by calling on 03 9000 0389.
Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.
References
Refractive Errors
https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/refractive-errors
Eyes – laser eye surgery
https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/eyes-laser-eye-surgery
Optical Properties of the Eye
https://www.aao.org/munnerlyn-laser-surgery-center/optical-properties-of-eye
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