Lower Femtosecond Laser Energy Levels Lead to Better Visual Recovery After Small-incision Lenticule Extraction for Myopia

Summary

Small-incision lenticule extraction (SMILE), the most recently developed refractive surgical technique, is being performed in a growing number of cases. This intrastromal keratomileusis using only a femtosecond laser is a new procedure that extracts the refractive lenticule through a small corneal incision ranging from 2 to 5 mm, with the absence of a flap and the preservation of the anterior-most stromal lamellae and Bowman's layer (except for the region of the small incision). Many studies have demonstrated that SMILE achieved comparable or superior efficacy, safety, and predictability to femtosecond laser -assisted in situ keratomileusis (FS-LASIK) and femtosecond lenticule extraction (FLEx). However, the recovery of visual acuity in the early postoperative period after SMILE is slower, compared to other refractive surgery techniques. Therefore, adjusting energy might improve postoperative visual acuity and recovery time after SMILE. Nevertheless, the optimal parameters drawn from a well-organized randomized study have yet to be elucidated. The purpose of this study was to investigate the optimal femtosecond laser energy, with the aim of improving clinical outcomes during the early postoperative period after SMILE for the correction of myopia. To this end, we used a 500 kHz VisuMax with spot-spacing control at energy levels lower than 115 nJ, based on the previous studies. Therefore, we prospectively compared visual outcomes of two groups randomly divided by different laser energies: one underwent SMILE using lower energy levels of 100, 105, and 110 nJ (L-SMILE), while the other group underwent SMILE at energy levels conventionally used of 115 to 150 nJ (C-SMILE).

Conditions

• Myopia

Interventions

PROCEDURE

SMILE procedure using lower energy (100, 105, and 110 nJ)

Based on the review of literature, we regarded SMILE using energy levels of 115 nJ or higher as 'conventional' energy-SMILE (C-SMILE). Since 500kHz VisuMax femtosecond laser used in this study had a threshold photodisruption energy level of 100 nJ, lowest energy level of L-SMILE was set at 100 nJ. Because the spot distance must be changed by approximately 1 μm when laser energy changed by 50 nJ, we could set the maximum laser energy to 150 (100 + 50) nJ as highest one of C-SMILE while keeping the spot distance constant. Finally, we established two groups divided by different laser energies: L-SMILE group using lower energy levels of 100, 105, and 110 nJ, and C-SMILE group using 'conventional', not higher, energy levels of 115 to 150 nJ.

PROCEDURE

SMILE procedure using conventional energy (115 to 150 nJ)

The SMILE procedures were conducted in the Eyereum Eye Clinic (Seoul, South Korea). The target postoperative refraction was emmetropia. The surgery, using standardized techniques, was performed by an experienced surgeon (D.S.Y.K.) using the VisuMax system. The surgical parameters used during SMILE were as follows: repetition rate of 500 kHz, pulse energy 100 to 150 nJ (100, 105, and 110 nJ, L-SMILE; 115 to 150 nJ, C-SMILE), spot distance 4.5 μm (regardless of FSL energy), cap thickness 120 μm, and side-cut width 2 mm in the 12-o'clock position with an angle of 90°. After the anterior (upper) and posterior (lower) delineated plane of the intrastromal lenticule were well defined, the anterior and posterior interface were dissected with a micro-spatula with a blunt circular tip and extracted with micro-forceps. The integrity of the lenticule was also checked subsequently.

Sponsors & Collaborators

• Yonsei University

  lead OTHER

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

NONE

Model

PARALLEL

Eligibility

Min Age

20 Years

Max Age

40 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2016-11-16

Primary Completion

2017-01-15

Completion

2017-01-15

Countries

• South Korea

Study Locations