Small-incision lenticule extraction (SMILE) is a flapless corneal refractive surgery technique performed entirely with a femtosecond laser; it involves the creation of a refractive lenticule with a femtosecond laser and removal of the lenticule from a small incision.1–3 This procedure has gained widespread acceptance because of its advantages over laser in situ keratomileusis (LASIK), including the lack of flap-related complications, faster visual recovery, better long-term biomechanical stability, less postoperative dry eye, and fewer induced aberrations.1 However, SMILE complications have been noted in a few case reports. Difficulties ranging from suction loss to corneal ectasia can occur during the procedure and postoperatively.
We report what we believe to be the first case of a leak in the curved suction contact glass of a VisuMax femtosecond laser (Carl Zeiss Meditec AG) during SMILE and describe a new approach for treating the resulting complication.
A 27-year-old woman had SMILE to correct compound myopic astigmatism in the right eye and myopia in the left eye. The preoperative assessment showed no ocular abnormalities. The uncorrected distance visual acuity (UDVA) was 20/200 in the right eye and 20/200 in the left eye. The corrected distance visual acuity was 20/16 with −3.50 −0.50 × 170 and 20/16 with −3.75 diopters sphere, respectively. The central corneal thickness on ultrasonic pachymetry was 546 μm in the right eye and 543 μm in the left eye.
The right eye had uneventful SMILE at Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. Once the left eye was properly fixated, the surgeon initiated automatic suction and started the laser treatment, which created 4 cleavage planes as follows:
- Lenticule cut (Figure 1, A): The posterior surface of the refractive lenticule was created using the spiral-in mode; the optical zone was 6.7 mm, and the cut was finished within 7 seconds.
- Lenticule side cut: The 360-degree side cut of the refractive lenticule was created with a side-cut angle of 110 degrees. When the lenticule side cut was complete, the central and nasal parts of the lenticule started to blur (Figure 1, B).
- Cap cut: The anterior surface of the refractive lenticule was created using the spiral-out mode. The cap thickness and cap diameter were 130 μm and 7.6 mm, respectively. Because the center of the lenticule was blurred, the cut in the anterior surface was observed within 15 seconds (Figure 1, C) and ended within 19 seconds (Figure 1, D).
- Cap side cut: A 30-degree side-cut small incision with a circumferential length of 2.0 mm was made and was positioned at 130 degrees with a side-cut angle of 90 degrees (Figure 1, E).
After the laser treatment, the refractive lenticule was manually dissected using microforceps; however, the anterior surface of the refractive lenticule was difficult to detach. The central blurring was considered an incomplete cut even though it was not a classic black spot, and the dissection was not attempted at that time. The posterior plane was separated uneventfully, and approximately one fifth of the posterior plane was dissected before the incision was closed; this might have caused the flap mode to immediately create the cap at that time. This was the first time this situation was encountered; thus, it was not known why it occurred and how to properly address it. The patient was comforted and told that she would be contacted when a strategy to address this issue was developed. The curved suction contact glass used in this procedure was transported to the manufacturer. The manufacturer determined that air was leaking from the suction contact glass (Figure 1, F) and recommended treating the eye with the flap mode to make the cap cut again.
One month later, the flap mode was used to create a cap in the left eye. The laser treatment of the flap created 2 cleavage planes as follows:
- Flap cut: The anterior surface of the refractive lenticule was created using the spiral-out mode. The flap diameter was 7.9 mm, and the flap thickness was 130 μm, the same as the cap thickness in the first treatment.
- Flap side cut: This plane may not occur, but manually stops when 8% processed.
After the laser treatment, the refractive lenticule was dissected through the side cut created by the first treatment and manually removed using microforceps, as in the uneventful SMILE procedure. One day after the second surgery, the patient had a UDVA of 20/20 in the left eye. By 1 week later, the UDVA in the left eye had improved to 20/16 and this acuity was maintained through the 6-month follow-up.
Although suction loss in the SMILE procedure is well known,4–6 to our knowledge this is the first case report of a leak from the suction contact glass during a SMILE procedure. The leak from the suction contact glass during the SMILE procedure resulted in an incomplete cut in the anterior surface of the lenticule. This situation is similar to the suction loss that occurs when more than 10% of the posterior surface of the lenticule is created. Therefore, we made the following assumption: There was a small hole in the suction contact glass (Figure 1, F) and as the laser treatment began, the amount of air entering the hole was not enough to influence the posterior surface of the lenticule and the lenticule side cut. However, as each step of the surgery was initiated, more gas entered the suction contact glass, resulting in an incomplete cut. In our case, the posterior surface of the lenticule cut was finished and an immediate femtosecond laser pass on the posterior surface of the lenticule might have caused an irregular lenticule surface and multiple lenticules, leading to free slivers of the corneal stroma and inducing irregular astigmatism. In femtosecond laser–assisted LASIK, it might be relatively easy to address this problem; however, this can lead to flap-related complications and biomechanical problems. Photorefractive keratectomy would solve this problem but could result in more postoperative pain, lower visual recovery, haze, and wound-healing problems. Using the flap mode to create a cap is the best choice in this situation. We used the flap mode to complete the SMILE procedure and avoid flap-related complications.
When using flap mode to create a complete cap, the eye must be properly fixated, similar to the first procedure. This is especially important in eyes with high astigmatism to prevent an eccentric ablation. The flap diameter must be larger than the intended cap diameter in the first treatment. Because the intended cap diameter was initially 7.6 mm in the first treatment, the second treatment was programmed with a 7.9 mm flap diameter, thus leaving a 0.3 mm gap between the flap side cut and lenticule cap side cut created in the first attempt. This effectively created the anterior surface of the refractive lenticule. In addition, this should be performed by a skilled refractive surgeon so the flap side cut is stopped in time to avoid a pseudo-SMILE procedure. To avoid the complications of a leak in the suction glass, it is important to ensure that the suction glass is functioning correctly.
In the current case, we used the flap mode and manually stopped the laser to produce a cap when the anterior surface of the lenticule could not be completely cut. It is important for surgeons to rule out irregular astigmatism by assessing preoperative and postoperative elevation topographies, to analyze preoperative and postoperative aberrations, and to compare preoperative and postoperative pachymetry.
None of the authors has a financial or proprietary interest in any material or method mentioned.
Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: all-in-one femtosecond laser refractive surgery. J Cataract Refract Surg 2011; 37:127-137
Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol 2011; 95:335-339
Hjortdal JØ, 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
Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology 2014; 121:822-828
Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg 2011; 37:1636-1647
Liu M, Wang J, Zhong W, Wang D, Zhou Y, Liu Q. Impact of suction loss during small incision lenticule extraction (SMILE). J Refract Surg 2016; 32:686-692