Development of low laser energy levels in small-incision lenticule extraction: clinical results, black area, and ultrastructural evaluation

Abstract

Purpose: To evaluate the outcomes of 4 low laser energy levels after small-incision lenticule extraction (SMILE) surgery. Setting: Zhongshan Ophthalmic Center, Guangzhou, China. Design: Prospective randomized clinical trial. Methods: This study evaluated consecutive patients who had SMILE to correct myopia or myopia with astigmatism. Eyes were placed into groups based on the laser energy used during surgery (ie, 105 nJ, 110 nJ, 115 nJ, or 120 nJ). All patients had a thorough ophthalmic examination preoperative and at 4 timepoints over 3 months postoperatively. Black areas and surface regularity of the extracted lenticules were observed and evaluated qualitatively and quantitatively. Results: The study comprised 124 eyes of 62 patients (40 women, 22 men), with 31 eyes in each laser energy group. The incidence of black areas was 45.16% (14 of 31 eyes), 12.90% (4 of 31 eyes), 16.13% (5 of 31 eyes), and 12.90% (4 of 31 eyes) for 105 nJ, 110 nJ, 115 nJ, and 120 nJ, respectively. The mean time for lenticule creation was the longest in the 105 nJ group (P = .015). The greatest increase in corneal thickness postoperatively occurred with 105 nJ (P < .05). Regression was highest in the 105 nJ group at 3 months (P < .01). However, corneal horizontal coma (C8) was lowest in the 105 nJ group at 1 week (P = .032). The lenticular surface in the 110 nJ group was the smoothest (P = .011). All contrast sensitivity values varied with time and recovered to preoperative levels by 1 week or 1 month. In all eyes, the uncorrected distance visual acuity and corrected distance visual acuity were good, with no statistically significant differences between the 4 energy groups. Conclusions: The 105 nJ group, in which the lowest energy was used, had the highest risk for black areas, serious postoperative corneal edema, and a significant healing response.

Prediction of Early Visual Outcome of Small-Incision Lenticule Extraction (SMILE) Based on Deep Learning

“…However, the incidence of black areas in our study eyes was 2.7% (ESM File 1). The incidence of BS determined in our study differs greatly from that reported in earlier studies, but the incidence of black areas is consistent with earlier studies, ranging from 0.33% to 11% [9,24,25]. Therefore, we believe that the terms 'black spots,' 'black areas,' or 'black islands' may not have been used consistently in previous publications [26,27].…”

“…Hence, we recognized that the BS are the tissue bridges between laser spots. This phenomenon was indirectly confirmed by Lin et al who estimated the black areas of four levels of low laser energy for SMILE surgery and found that the lowest energy used had the largest area of BS [24]. The surface quality of scanning may be mainly determined by two factors: (1) the distance of laser spots and the delivered energy of per pulse; and (2) tissue reaction for photo disruption [28,29].…”

Twelve-month outcomes of a new refractive lenticular extraction procedure

“…As for black spots, in our experience black spots were observed as isolated punctual micro-regions, and they seemed more related to debris at the cornea-laser interface than to instability of the laser energy. 29 We think that one reason why they did not interfere with the dissection can be the fact that ATOS is using a relatively high Repetition Rate, in the MHz regime, associated with a low energy per pulse with dense overlap. 30 Thus, many tiny microbubbles are created close together; probably stochastically homogenizing the ease of dissection.…”

Effect of femtosecond laser cutting parameters on the results of small-incision lenticule extraction

“…In addition, a mismatch of spot distance and energy levels may cause overlapping of the cavitation bubbles, and the resulting opaque bubble layer may impair the subsequent laser beam, leading to surface microirregularities. 9 Furthermore, higher laser energy levels were reported to be associated with greater keratocyte death and inflammation in FS-LASIK. 20 Notably, not only was the laser pulse energy higher in Group 1 but the cumulative energy as well.…”

“…8 In contrast, pulse energy that is too low can induce black areas during treatment, which may hinder the surgical separation of the lenticule, causing postoperative corneal edema and impaired visual outcomes. 9 Corneal microirregularities can result in straylight, and 1 study showed that the thickness of new irregular stromal tissue formed after photorefractive keratectomy is related to increased objective corneal scattering. 10 Different surgical techniques induce different cellular responses; for example, photorefractive keratectomy increases transforming growth factor b1 expression in keratocytes, resulting in corneal haze.…”