SMILE versus custom LASIK
Can SMILE® compete with topography-guided custom LASIK for most refractive surgery patients?
Vance Thompson MD
Can SMILE® compete with topography-guided custom LASIK for most refractive surgery patients? The answer may depend upon the needs of individual patients, according to debaters at the JCRS Symposium at the 38th Congress of the ESCRS, held virtually for the first time.
Arguing for SMILE was Timothy J Archer MA (Oxon), DipCompSci (Cantab), PhD, of London Vision Clinic, London, UK. He allowed that topography-guided treatment gives excellent results for therapeutic purposes, such as correcting irregular astigmatism, enlarging optical zones and re-centring ablations. But it is a complex procedure that most patients don’t really need, and SMILE is a less-invasive alternative with equivalent visual outcomes.
Arguing for custom LASIK, Vance Thompson MD, of Vance Thompson Vision, Sioux Falls, South Dakota, USA, noted that it is necessary for some patients and can produce better low-contrast visual outcomes, making it a better choice for many patients. He agreed, though, that some patients require SMILE benefits such as reduced dry eye risk, and he prefers it for many patients who do not need topography or wave-front guided procedures.
Dr Archer pointed out that most patients have very low corneal aberrations with spherical aberration (SA) most common, averaging just 0.14 microns up to 0.42 at two standard deviations. Moreover, a small amount of SA is beneficial since it increases depth of field. For coma, the average is 0.19 and 95% of eyes have 0.42 micron or less.
“Topography-guided treatment might be an option for this 5%,” Dr Archer said.
For the other 95%, topography-guided procedures introduce complexities that potentially lead to errors. These include deciding which refraction and how much astigmatism to treat, since both are influenced not just by anterior corneal topography but also the posterior cornea, crystalline lens, retinal irregularities and neuroadaptation.
Corneal aberrations are often partially offset by internal aberrations leaving a low level of total aberrations.
“If you treat the corneal aberrations entirely you run the risk of unmasking significant internal aberrations.”
Similarly, topographical coma can be measured as “pseudo” cylinder, so treatment based on manifest refractive cylinder can lead to significant overcorrection as both the coma and the pseudo-cylinder would be included in the treatment, Dr Archer said.
Tear film issues, contact lens use and measurement errors are other confounding factors.
“All this adds up to a lengthy and complex treatment planning process requiring trained and skilled operators.”
SMILE is a better alternative for most patients, Dr Archer said. As a less invasive “keyhole” surgery requiring no flap, SMILE is more attractive to patients, especially those participating in contact sports or other extreme activities.
Multiple studies also show that SMILE produces less dry eye than LASIK as measured by Schirmer’s test and tear break-up time (Singh Sambhi RD et al. Can J Ophthalmol. 2020 Apr;55(2):99-106). Symptoms are also significantly less three years out (Han T et al. Health and Quality of Life Outcomes. 2020; 18:107); and SMILE is less disruptive to corneal nerve fibres short term (Recchioni A et al. Cornea. 2020 Jul; 39(7):851-857.). Furthermore, the biomechanical advantages of SMILE enables the use of larger optical zones, leading to less SA induction (Spiru B et al. J Refract Surg. 2018 Jun;34(6):419-423).
With 10 years’ history, SMILE is a mature procedure that produces visual outcomes similar to LASIK, according to data on nearly 4,000 patients with 12 months;’ follow-up at Dr Archer’s clinic. Of note is the importance of optimising the energy and spot spacing settings for each individual laser, and this goes some way to explain some of the reports of lower outcomes in SMILE compared to LASIK. This is most relevant in the US, where the energy and spot spacing settings were fixed until the second FDA approval in 2019. It is also highly predictable and stable, accurately corrects cylinder, and improves contrast sensitivity, even in patients with high myopia up to -13.00D spherical equivalent, he reported. And patient satisfaction is high. So, SMILE can compete with custom LASIK for eyes with normal visual aberrations, Dr Archer concluded.
Custom LASIK advantages
Dr Thompson noted that he prefers SMILE for many patients, but some require custom procedures. In addition to irregular astigmatism that can benefit from topography-guided treatment, patients with significant higher-order aberrations can benefit from wavefront-guided LASIK.
Custom LASIK can produce better vision results, Dr Thompson said. He referenced a study involving 80 patients by Edward E Manche of Stanford University presented at the ESCRS meeting comparing SMILE and wavefront-guided LASIK outcomes. More wavefront-guided LASIK patients had 20/20 uncorrected distance vision at one day after surgery, but visual outcomes were similar at one year. However, more LASIK patients gained one line of corrected VA and they had significantly better VA at 5% and 25% contrast than SMILE patients.
Some other studies show better accuracy with custom LASIK than current SMILE, Dr Thompson added (Kanellopoulos AJ. J Refract Surg. 2017 1;33(5):306-312. Khalifa MA et al. J Refract Surg. 2017 1;33(5):298-304). LASIK is also better for treating patients with astigmatism below 0.75D, he added.
However, while vision and optics are central, treatment decisions involve other factors as well. Patients are often well informed about dry eye and the impact of LASIK flaps on corneal biomechanics, Dr Thompson said. In addition to leaving a stronger cornea, SMILE does less damage to corneal nerve fibres, translating into less dry eye.
“When I have a patient concerned about the dry eye of LASIK, they are comforted by this fact,” he noted.