Advances in refractive surgery: Spotlight on small incision lenticule extraction

(Image Credit: AdobeStock/Generative ART)

In this Ophthalmology Times EyeView, John Doane, MD, FACS, offered insights into small incision lenticule extraction (SMILE) for patients with simple myopia and compound myopic astigmatism and discussed the latest advancements in laser technology that enhance the surgical experience and precision of the procedure. Doane is with Discover Vision Centers in Kansas City, Missouri.

SMILE

Although there are comparisons to photoablation, photorefractive keratectomy (PRK), and laser in situ keratomileusis (LASIK), SMILE differs from those procedures. First, a 3-dimensional piece of tissue is created by performing a photodisruptive layer on the back corneal surface (a refractive cut) using a Zeiss laser.

This is followed by a cap photodisruption that creates a lenticle of tissue that acts as a positive meniscus lens to treat myopia or compound myopic astigmatism that will flatten the corneal center, Doane explained.

In the US, he noted, patients are good candidates for SMILE if they have simple myopia from 1 to 10 D—possibly extending to 11.5 D—and compound myopic astigmatism up to 3 D and as little as 0.75 D of astigmatism. A military study is under way to investigate the potential for treating 0.5 D and up to 4 D of astigmatism.

“I currently perform SMILE to treat 90% to 95% of my patients with simple myopia and compound myopic astigmatism,” Doane explained. Hyperopia and mixed astigmatism cannot be treated with SMILE. The rest of his patients undergo either PRK or LASIK. “I tell surgeons that if a patient is a good candidate for LASIK, they are a good candidate for SMILE,” he said.

SMILE vs LASIK

The corneal structural integrity postoperatively is greater with SMILE compared with LASIK with the same parameters. The postoperative medications are identical for both procedures.

“One difference is that there are no limitations for the SMILE patients. There are no concerns about eye rubbing or displacing a flap as with LASIK,” Doane said. “I feel more comfortable telling patients that they can resume full activities the day after SMILE and eye shields are not needed. Visual recovery is essentially the same with the 2 procedures. In addition, SMILE patients have less discomfort.”

Laser advances to enhance SMILE

The laser developed for SMILE, the VisuMax 500 (Zeiss), was in trials beginning in 2012. It was approved to treat simple myopia in 2015 and compound myopic astigmatism about 18 months later. The later generation, the VisuMax 800, was built for SMILE in 2024. “There is a distinct difference between the surgical procedure, the device, and the footprint from the previous laser,” Doane said.

First, the laser’s speed is much faster. The photodisruption with the later generation is 4 times faster, at 2 million spots/s vs 500 spots/s, and the total procedure time is 9 seconds vs 26 seconds. However, there is perhaps a more important factor.

“Due to the speed of the laser, we think that the spots precede formation of the opaque bubble layer,” Doane explained. “The tissue dissection that is created with the pattern of disruption is much more defined, which makes the mechanical dissection so much easier.”

Another difference, for example, is if a surgeon tried to perform SMILE previously on a patient but found it too difficult, the latest laser generation makes SMILE a different procedure. Doane recounted that the more difficult SMILE procedures had been in patients with –3 D or less of myopia because of the thinner lenticules.

“The VisuMax 800 is a total game changer in that the dissections have become sufficiently easier to facilitate comfortably treating from –1 to –3 D of myopia,” Doane pointed out.“In contrast, surgeons using the VisuMax 500 would not do cases with less than 3 D of myopia; they would perform either PRK or LASIK.”

For higher corrections, the VisuMax 800 also has made the SMILE procedures easier. “The later generation is just a different laser that provides a totally different experience. It has increased my confidence in my ability to obtain the desired outcome,” he stated.

A challenge with SMILE is the learning curve, which surgeons new to the procedure should realize. The manual dissection is probably the biggest hurdle.

“However, importantly, when comparing SMILE and LASIK, the enhancement rate worldwide is about [one-third] that of LASIK,” Doane concluded. “There is no question in my mind that SMILE is a more precise procedure with a lower enhancement rate.”

John Doane, MD, FACS

E: jdoane@discovervision.com

Doane is a board-certified ophthalmologist and LASIK surgeon with Discover Vision Centers in Kansas City, Missouri. He is one of 5 refractive surgeons in the country involved in the clinical trials for SMILE.