How Does LASIK Work?

How does LASIK work?

The idea of getting rid of your eyeglasses or contact lenses can be pretty appealing, especially if you’ve been dependent on these optical aids for a number of years. Who wouldn’t want to be able to open their eyes in the morning and be able to see clearly out the window immediately? Or not have their glasses steaming up in the kitchen or whenever you wear a facemask? Or not have to constantly clean and disinfect their contacts and then remember when they’re about to run out and need to order more?

At this current time, the only alternative to correcting vision with glasses or contacts is refractive surgery (no, there is no evidence that eye exercises work). But surgery, for many people, is a big step and a scary one, too. One of the more popular and well-known refractive surgery techniques is LASIK.  For some people, LASIK is exclusively synonymous with laser eye surgery. While this is not 100 per cent accurate (lasers can be used for many types of eye procedures), let’s focus on how LASIK works.

 

What is Refractive Surgery?

Refractive surgery is a group of procedures designed to permanently correct the refractive error of an eye. Refractive error is a mismatch of the eye’s focusing power (determined by the cornea at the front of the eyeball and the crystalline lens farther inside) and its axial length (literally the length of the eyeball). If the eye’s focusing power is too strong for its axial length, we end up with a focal point of light that’s too short – it falls in front of the retina. This is called myopia (short-sightedness). If the focusing power is too weak, the focal point falls behind the retina. This is hyperopia (long-sightedness). To have sharp vision, we want the focal point of light to fall right onto the retina.

Astigmatism is another type of refractive error. Unlike short- and long-sightedness, this is typically caused by an uneven curvature of the cornea (and sometimes also the lens). Instead of being perfectly rounded like the curves of a basketball, the cornea is steeper along one axis, like a football. This results in light coming to different points of focus depending on how it passed through the cornea. Either one or neither of these focal points may fall on the retina, leading to imperfect vision no matter what distance you’re looking at.
There are a number of different types of refractive surgery procedures, and not all of them involve lasers. They include:

  • LASIK (laser assisted in situ keratomileusis)
  • PRK (photorefractive keratectomy)
  • SMILE (small incision lenticule extraction)
  • RLE (refractive lens exchange, also known as clear lens exchange)
  • ICL (implantable collamer lens or implantable contact lens)

There are also a number of variations of the main procedures mentioned above, such as epi-LASIK, ASLA, and Presbyond.

Epi-LASIK, also known as LASEK, is Dr. Michel’s preferred laser vision correction technique and he’s been using it successfully for years! It combines the best of both PRK LASIK and regular LASIK. During LASEK laser eye surgery, the epithelial layer of the cornea is removed by loosening the adhesions of the epithelium (this is where the “epi” in epi-LASEK comes from) to the underlying membrane with an alcohol solution, and then gently lifting or folding the epithelium aside with a blunt tool. Unlike PRK LASIK, the epithelial layer is retained and not discarded, and there are no sharp blades involved.

LASIK has been around for about 30 years. It has a great success rate, over 90%, and is associated with a low risk of complications.

 

What Is LASIK and How Does It Work?

Thinking about putting your eyeballs under the proverbial knife is enough to make anyone feel a bit squeamish. Understanding more about the LASIK procedure may help to alleviate some of this anxiety (or possibly make you feel even more anxious). Either way, here it goes!
LASIK is a type of corneal refractive surgery that does utilize laser tools. The basic idea is to change the shape of the cornea – one of those components that determine refractive error – so that light can focus sharply onto the retina. Adjusting the curvature of the cornea is performed through a process called photoablation. Basically, the laser is used to vaporize parts of the corneal tissue. All corneal refractive techniques are based on this idea.

Before you’re booked for your laser vision correction, your eye specialist will check your eyes for suitability for LASIK, as well as chat about what to expect from the operation. (And importantly, give you quotes). If everything checks out, under the laser you go!
On the day of your procedure, you’ll be advised to have someone drive you there. Although your vision may be quite reasonable soon after having LASIK, it still won’t be quite right so it’s best to have someone else take the wheel. Usually both eyes are treated at the same time.

You’ll have your eyes anaesthetized with topical eyedrops and if you’re feeling really nervous, you may ask for a mild sedative.

Once you’re comfortable (or at least as comfortable as you can be), the surgeon will create a thin flap out of the outer corneal layers. This flap is gently peeled open and set to the side, while still being attached to the eye via a hinge. Forming the flap can either be done with a bladed instrument known as a microkeratome, or with a femtosecond laser tool. By moving aside these superficial corneal layers, another laser known as an excimer laser can be applied to the deeper corneal tissues for photoablation. Once the ablation is finished, the flap is replaced and will usually self-seal over time without stitches.

You’ll have protective plastic shields placed over your eyes and be sent home with a list of post-operation instructions. There is typically a follow-up appointment the day after the operation and again a month or so after that.

 

Am I Suitable for LASIK?

A big part of the pre-op consultation is ensuring that you meet the eligibility criteria to be able to safely undergo the LASIK procedure. If you’re found to be unsuitable, fear not. There may still be other options available to you, such as PRK or ICL. Each person (and eyeball) is unique, so while these are general criteria, there may be other factors specific to your situation.

  • Age. To make refractive surgery worthwhile, your eyeball needs to have stopped growing and changing. This usually happens around the age of 18 to 21 years, where your surgeon will want to see that your prescription has been stable for at least the past 12 months. At the other end of the spectrum are those in older age who are experiencing the effects of presbyopia. Presbyopia results in difficulties with near focus, and is a normal part of aging. Undergoing LASIK won’t help your reading vision, and so your surgeon will likely recommend a different technique such as RLE if you’re over the age of 55 or so.
  • Corneal thickness and refractive error. These two eligibility criteria go hand-in-hand. The higher your prescription, the more corneal tissue that needs to be removed. Therefore, the more corneal tissue you need to have in the first place. If your corneas are too thin, photoablating the amount of tissue required to fix your prescription will result in an extremely thin cornea remaining. This can put your eye at risk of all sorts of problems, including a distortion of the cornea from the outward pressure of the eyeball. If your corneas are too thin for LASIK, you may still be suitable for PRK. The general treatment range for LASIK is short-sightedness up to -10 diopters, long-sightedness up to +5 diopters, and astigmatism up to -5 diopters. But remember, it also does depend on your corneas.
  • Eye health. While LASIK can fix the imperfect vision caused by refractive error, it can’t fix vision that’s limited by other problems such as eye diseases or scarring. If you have a cataract, for example, undergoing LASIK isn’t going to get light through that cloudy lens any better than glasses would. Other possible eye diseases that could make you unsuitable for LASIK include extensive corneal scarring, macular disease, or amblyopia (lazy eye). Severe dry eye is another cause for hesitation for LASIK as the LASIK operation can exacerbate this condition.
  • Pregnancy and breastfeeding. Because the hormonal changes caused by pregnancy and nursing can affect your prescription temporarily, it’s best to wait until after before having LASIK eye surgery.
  • Certain systemic diseases. Some conditions can impair your body’s ability to heal properly, which puts your eyes at risk of infection or prolonged inflammation and damage if you were to have LASIK surgery. These include autoimmune diseases such as Sjogren’s syndrome, rheumatoid arthritis, AIDS/HIV, and diabetes. The medications associated with some diseases can also affect post-op healing or increase your risk of dry eye syndrome. There is no overall consensus between surgeons about which diseases do or don’t result in immediate elimination from LASIK candidacy, so it’s best to discuss this with your surgeon.

If you’re interested in whether LASIK is for you, the best thing to do is to get in touch with a refractive eye surgeon in your area. Who knows, you may soon find yourself spectacle and contact lens-free!

 


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