In our refractive surgery practice, Eyes of York Cataract and Laser Center, we are committed to performing a range of cutting-edge procedures. We strive to offer our patients a comprehensive array of options that can effectively correct their refraction — including LASIK, PRK and refractive lensectomy with implantation of presbyopic IOLs.
We acquired the VisuMax laser (Carl Zeiss Meditec) for small incision lenticule extraction (SMILE) when it was time to replace our femtosecond laser for LASIK flaps. We believed having a femtosecond laser with multiple refractive functions would expand our potential refractive surgery population. When the FDA expanded SMILE approval from -1.00 to -10.00 D and cylinder up to 3.00 D, it extended that potential even more.1 As a procedure, SMILE fits our mission to grow our refractive practice in the community.
EXPLORING THE BENEFITS
SMILE provides numerous benefits. First, SMILE appeals to patients who prefer or need a flap-less procedure — SMILE requires a smaller incision than LASIK and does not carry the small risk of flap dislocation. The “keyhole/pocket” nature of SMILE produces a stable immediate postoperative cornea, and a lengthy description of the pros and cons of LASIK vs. SMILE is rarely necessary for patients to understand this point.2
Two other advantages: “faster dry eye recovery and an extended range of treatment due to better spherical aberration control as a result of better biomechanics,” as reported by Dan Reinstein, MD, and his colleagues.2 After laser vision correction using LASIK or PRK, dry eye improves by 12 months postoperatively.3 When my SMILE patients have significant dry eye issues, they resolve over a shorter period than with LASIK or PRK.
Also, research shows SMILE is associated with a reduced risk of dry eye compared with LASIK,4 and I have noticed my SMILE patients have less postoperative discomfort and visual fluctuations.
Postop day one vision is usually 20/20 with my LASIK patients. Although the postoperative day one vision with SMILE is excellent, it still does not beat LASIK. However, we are getting closer and closer.
The day after surgery, SMILE patients’ vision averages 20/25 to 20/30, which will get better. In my practice, patients can expect their vision to improve one or two lines over their first-week postoperative vision. In a multicenter clinical trial of spherocylindrical myopia correction with SMILE, uncorrected visual acuity was 20/20 or better in 84% of eyes and 20/40 or better in 99% of eyes at six months.5
With the new SMILE software that expanded the range of myopia treatment to patients with astigmatism, we have also be able to adjust the laser energy and spot size of our treatments to improve postoperative day-one visual acuity. In fact, many surgeons now achieve 20/20 vision the day after surgery. When you begin using the lower energy settings, dissection becomes slightly more difficult; thus, surgeons need to balance the procedure for their practice.
Research varies on corneal stability.6-8 The biomechanical differences between SMILE and LASIK have been studied in cadaver eyes and using computational finite element analysis. The consensus of this research is that SMILE delivers a more stable postprocedure cornea because the anterior corneal fibers are not cut vertically to the extent they are with LASIK. Furthermore, stromal and epithelial remodeling have been shown to be less in SMILE than LASIK for the same level of vision correction, which may account for the better control of spherical aberrations with SMILE.9
I still consider myself a beginning SMILE surgeon and prefer to conservatively offer SMILE to patients with -2.00 D to -7.50 D myopia and those with astigmatism as high as 2.75 D.
In general, patients who are candidates for LASIK are also candidates for SMILE. However, some patients who are not good candidates for LASIK may qualify for SMILE. Higher levels of myopia respond extremely well to SMILE. The biomechanical advantages of SMILE allow for the use of larger optical zones, which decreases higher-order aberrations for these larger corrections. Furthermore, in my experience, those at higher risk for dry eye issues postoperatively may benefit more from SMILE.
It is also important to consider patients’ occupation or hobbies when deciding on a procedure. Those that take part in activities with a greater risk of LASIK flap dislocation will benefit more from SMILE. Examples of these patients include police officers on special teams, military personnel, firefighters, teachers who work with special needs children, contact sports enthusiasts and pet groomers.
WHEN TO AVOID SMILE
We avoid SMILE in patients who are highly anxious, opting for PRK instead. Patients who cannot remain still for the 23- to 25-second SMILE laser application are not good candidates. Even if they do not break suction, it’s problematic when patients move during the femtosecond laser treatment.
If patients have a large angle kappa, we can more easily adjust with the excimer laser for LASIK or PRK, compared with SMILE. Also, patients whose eyes water profusely are more difficult for me to manage with SMILE.
Finally, any patients who fail the preoperative workup are rejected for any laser vision correction surgery. Typical diagnoses include keratoconus, severe dry eye, inadequate pachymetry and refractions outside the treatment parameters. I prefer a residual stromal thickness of 325-350 µm with SMILE.
PEARLS FOR ACHIEVING OPTIMAL RESULTS
Based on my experience with SMILE, here are my tips for successfully incorporating this procedure into your practice. I also recommend “The Surgeon’s Guide to SMILE: Small Incision Lenticule Extraction,” by Dan Reinstein, MD, and his colleagues.2
- Perform preoperative workup. Advanced corneal topography with wavefront analyses and posterior corneal capabilities should be used to plan treatments and minimize the risks of ectasia — this is standard for any laser vision correction procedure. We also perform pupillometry in scotopic and mesopic conditions and assess angle kappa. We also consider the preoperative workup as an opportunity to partner with patients. Sharing the preoperative testing images is a powerful tool in building relationships with patients and facilitates compliance during and after surgery.
- Address dry eye. It is important to diagnose and aggressively treat dry eye before surgery; if left untreated, dry eye can negatively impact any laser vision correction outcome. In addition to tear film tests, we perform meibography and require thermal pulsation before laser vision correction for moderate disease. Patients with advanced meibomian gland disease are rejected for laser vision correction. Also, if dry eye does not respond after several months of management, we do not perform laser vision correction.
- Assess patients’ needs. In addition to asking patients about their careers, interests and expectations, we also consider how they will tolerate laser vision correction and postoperative recovery. Are they overly sensitive to having their eyes touched? If so, they probably will be more comfortable with PRK. Do they want a quick return to normal activities? In these cases, I consider SMILE.
- Explain the procedure. Before surgery, I set patients’ expectations by describing each step of the SMILE procedure. If they are cooperative, the process is extremely straightforward. The VisuMax is a gentle laser, so patients may not feel it touch their eye; therefore, I instruct them to listen closely for my verbal cues. I reassure patients that I will instruct them throughout the entire procedure as to what they will see and when. I explain that they will first see a green light, on which they will fixate and then ignore, staring past it “like a zombie.” I also describe the two waves of whiteout they will see as the bubble layers pass in front of their vision. Finally, I explain that after the laser is complete, I will connect all the bubbles in the pocket and slip the lenticule out.
- Implement useful tools. As every good mechanic knows, having the proper tools makes the job proceed more easily. I recommend trying several different SMILE instruments before choosing your preferences. I like a Lieberman type of adjustable speculum with solid blades. For lenticule removal, I use the Guell femto double instrument to enter the pocket and for dissection. Lastly, I have found the Rupal Shah lenticule forceps to be the best grasping instrument to extract the lenticule. Additionally, I recently began using the iLight by Surgilum, a magnetic light source that illuminates the eye inferiorly. With the indirect illumination, I can easily see the edge of the lenticule and identify my instrument position anteriorly or posteriorly. Also, patients do not stare at a bright microscope light. I now remove the lenticule much more quickly and have become slicker with the procedure (Figure, page 33).
- Treat astigmatism. The SMILE procedure was recently approved by the FDA to treat myopia with astigmatism.1 With any type of refractive surgery, you begin with the “usual” nomogram and titrate. Fortunately, much of this has been worked out. Many studies10-15 have reported an undercorrection of approximately -0.25 D for both sphere and cylinder when using the manifest refraction. The current recommendation is to add 10% to both sphere and cylinder treated before developing a personalized nomogram. That said, with personalized nomograms, there is a tendency to overcorrect when treating against-the-rule cylinder, and further refinement will be necessary. Currently, I add 0.25 D to 0.50 D to the sphere for treatment, depending on the patient’s ability to accommodate. When treating with-the-rule cylinder, I do not adjust. For against-the-rule cylinder greater than 1.50 D, I subtract 0.25 D to 0.50 D. Of course, with more surgeries, our personal nomograms become tighter and the results even better.
- Preparing for postop. Many patients have perfect vision on postoperative day one, but we cannot predict this for certain. It is always better to under-promise and over-deliver. So, we explain to patients that their vision will be good the first postoperative day and improve gradually after that. As for postoperative medication, in addition to the topical steroid and antibiotic drops, we also prescribe an oral methylprednisolone dose pack. We find this decreases the frequency and duration necessary for their prednisolone ophthalmic drops.
Successful refractive surgeons strive to meet each patient’s unique needs with the best technology available. If you perform laser vision correction but you have not learned about SMILE, you and your patients are missing the opportunity to benefit from it.
By understanding the advantages of SMILE and taking steps to ensure its success, surgeons can expand their refractive surgery portfolio with a procedure that can deliver a better experience. OM
- VisuMax Femtosecond Laser - P150040/S003. U.S. Food and Drug Administration. https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprovalsandClearances/Recently-ApprovedDevices/ucm624482.htm . Accessed March 28, 2019.
- Reinstein DZ, Archer TJ, Carp GI. The Surgeon’s Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: Slack Incorporated, 2018.
- Murakami Y, Manche EE. Prospective, randomized comparison of self-reported postoperative dry eye and visual fluctuation in LASIK and photorefractive keratectomy. Ophthalmology. 2012;119:2220-2224.
- Denoyer A, Landman E, Trinh L, et al. Dry eye disease after refractive surgery: comparative outcomes of small incision lenticule extraction versus LASIK. Ophthalmology. 2015;122:669-676.
- Summary of Safety and Effectiveness Data (SSED), VisuMax Femtosecond Laser. FDA. https://www.accessdata.fda.gov/cdrh_docs/pdf15/p150040s003b.pdf . Accessed March 15, 2019.
- Piru B, Kling S, Hafezi F, Sekundo W. Biomechanical properties of human cornea tested by two-dimensional extensiometry ex vivo in fellow eyes: femtosecond laser-assisted LASIK versus SMILE. J Refract Surg. 2018;34:419-423.
- Sinha Roy A, Dupps WJ Jr, Roberts CJ. Comparison of biomechanical effects of small-incision lenticule extraction and laser in situ keratomileusis: finite element analysis. J Cataract Refract Surg. 2014;40:971-980.
- Raevdal P, Grauslund J, Vestergaard AH. Comparison of corneal biomechanical changes after refractive surgery by noncontact tonometry: small-incision lenticule extraction versus flap-based refractive surgery — a systematic review. Acta Ophthalmol. 2019; 97:127-136.
- Shetty R, Francis M, Shroff R, et al. Corneal biomechanical changes and tissue remodeling after SMILE and LASIK. Invest Ophthalmol Vis Sci. 2017;58:5703-5712.
- Chan TC, Ng AL, Cheng GP, et al. Vector analysis of astigmatic correction after small-incision lenticule extraction and femtosecond-assisted LASIK for low to moderate myopic astigmatism. Br J Ophthalmol. 2016;100:553-559.
- Hjortdal JO, Vestergaard AH, Ivarsen A, Ragunathan S, Asp S. Predictors for the outcome of small-incision lenticule extraction for Myopia. J Refract Surg. 2012;28:865-871.
- Agca A, Demirok A, Cankaya KI, et al. Comparison of visual acuity and higher-order aberrations after femtosecond lenticule extraction and small-incision lenticule extraction. Cont Lens Anterior Eye. 2014;37:292-296.
- Zhang J, Wang Y, Wu W, et al. Vector analysis of low to moderate astigmatism with small incision lenticule extraction (SMILE): results of a 1-year follow-up. BMC Ophthalmol. 2015;15:8.
- Ivarsen A, Hjortdal J. Correction of myopic astigmatism with small incision lenticule extraction. J Refract Surg. 2014;30:240-247.
- Kobashi H, Kamiya K, Ali MA, et al. Comparison of astigmatic correction after femtosecond lenticule extraction and small-incision lenticule extraction for myopic astigmatism. PLoS One. 2015;10:e0123408.