SMILE laser eye surgery is the latest addition to the array of laser vision correction procedures available that allow you to see clearly with the naked eye. But what makes it different from other corneal procedures like LASIK and PRK?
PRK, LASIK and SMILE laser
PRK / ASLA
Our practice (Vision Eye Institute in Sydney’s Chatswood area) first introduced laser eye surgery to Australia in 1991 in the form of PRK. PRK has since undergone a number of refinements and is now known as Advanced Surface Laser (or ASLA). As you can see in the diagram below, it involves reshaping the surface of the cornea. To do this, a particular kind of laser called an excimer laser removes corneal tissue by vaporising it away. The resulting new corneal shape allows clear focus without glasses or contacts.
ASLA continues to be performed around the world and gives fabulous visual outcomes but it has largely been overtaken in the popularity stakes by LASIK. Why? Because ASLA reshapes the top layers of the cornea, it causes discomfort during the initial days of healing and often takes a week or more to achieve functional vision for normal day-to-day activities. In a busy world, nobody likes downtime and certainly not sore eyes, not even for a day or two.
LASIK, in contrast, gives almost instant visual results and discomfort during healing is rare. As you can see in the diagram, LASIK involves the creation of a superficial flap of corneal tissue using another kind of very fast-pulsing laser called a femtosecond laser. The flap is folded back so that the excimer laser can reshape the underlying layers and bypass the superficial layers completely. So, two different lasers are used during the procedure. You usually have little or no downtime with LASIK, apart from the day of the procedure itself. LASIK also gives excellent visual outcomes and covers a wide range of prescriptions from about +4 to -10. However, you need to have adequate corneal thickness to not only correct the error but to create the flap as well, and this makes LASIK unsuitable for some thinner corneas that would be suitable for ASLA or SMILE.
Both LASIK and ASLA remove tissue from or near the surface of the cornea and this is now being shown to impact on the overall strength and integrity of the cornea compared to SMILE laser. LASIK also impacts temporarily on the corneal nerve supply and often results in a period of dry eyes. Where this occurs, it usually disappears within a month or two but it is one reason why we don’t perform LASIK on patients with chronic dry eye conditions.
SMILE laser removes corneal tissue in a different way to LASIK and ASLA. An excimer laser is not used at all during this procedure, so gone are many of the hallmarks of traditional laser vision correction. A femtosecond laser is used to define a tiny lens-shaped disc of tissue from within the cornea and this lenticule is removed through a keyhole (3mm) incision. Why is it different to the excimer laser? The femtosecond laser is quiet and doesn’t create the slight odour that sometimes occurs with the excimer laser. Neither is there any need to change from one laser to another during the procedure.
And the outcomes? Just like LASIK and ASLA, SMILE laser gives excellent visual outcomes and similarly has a very high safety profile.
Currently, SMILE laser is only available for moderate to high levels of myopia (or short-sightedness) and astigmatism, from about -3 to -10 dioptres, so it’s not for everyone. Clinical evidence continues to emerge that SMILE laser may give better results for patients with higher errors. It is also a more appropriate procedure for patients at risk of dry eye.
The table below indicates some of the differences between SMILE, LASIK and ASLA.
Each of the three procedures still has its role to play. The SMILE technique is a more modern way to perform laser eye surgery and is the procedure of choice for certain groups of patients, especially those with higher errors or drier eyes.