Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction.
Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery.
The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries.
The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.
Vestergaard AH
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Visual and Refractive Outcomes of Photorefractive Keratectomy and Small Incision Lenticule Extraction (SMILE) for Myopia.
To compare the refractive outcomes of small incision lenticule extraction (SMILE) with photorefractive keratectomy (PRK) using an aberration-free ablation profile.
One eye of patients diagnosed as having myopia for bilateral refractive correction was randomly allocated to either PRK or SMILE. The primary outcome measures included refractive efficacy, predictability, safety, stability, corneal aberrations, and adverse events. Patients were followed up for 1 year postoperatively; postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, and corneal aberrations were recorded and compared with preoperative data.
Thirty-nine patients in the PRK group and 35 patients in the SMILE group completed the study. The mean preoperative spherical equivalent refractions were -3.27 ± 0.62 diopters (D) for the PRK group and -3.56 ± 1.12 D for the SMILE group. The average postoperative spherical equivalent refractions were -0.26 ± 0.29 and -0.43 ± 0.38 D for the PRK and SMILE groups, respectively (P = .06). Total higher order aberrations in the 6-mm central corneal zone were significantly higher in the SMILE group (0.21 ± 0.10 µm) than in the PRK group (0.09 ± 0.03 µm) (P = .01) 12 months postoperatively. However, no statistically significant differences were found among spherical, trefoil, and coma aberrations between the groups.
The refractive results of PRK with aberration-free aspheric ablation are similar to those of SMILE in eyes with low myopia. The induction of coma, spherical, and trefoil aberrations did not statistically differ after both surgeries, but the total higher order aberrations after SMILE were significantly higher than PRK with aberration-free aspheric ablation. [J Refract Surg. 2016;32(9):604-610.].
Yildirim Y
，Olcucu O
，Alagoz C
，Basci A
，Agca A
，Yasa D
，Ozgurhan EB
，Demirok A
... -
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Comparing corneal higher-order aberrations in corneal wavefront-guided transepithelial photorefractive keratectomy versus small-incision lenticule extraction.
To evaluate the changes in corneal higher-order aberrations (HOAs) after corneal wavefront-guided transepithelial photorefractive keratectomy (PRK) and small-incision lenticule extraction (SMILE).
Yonsei University College of Medicine and Eyereum Eye Clinic, South Korea.
Retrospective case series.
Medical records of patients having either corneal wavefront-guided transepithelial PRK or small-incision lenticule extraction were examined. The root-mean-square total HOAs, 3rd-order coma aberration, and 4th-order spherical aberration were measured preoperatively and 6 months postoperatively. Independent t tests and analysis of covariance were used to compare changes in corneal HOAs between the 2 groups.
The study comprised 77 eyes having corneal wavefront-guided transepithelial PRK and 81 eyes having small-incision lenticule extraction. The total HOAs and spherical aberration increased after transepithelial PRK (all P < .001), whereas coma aberration was stable after transepithelial PRK. The total HOAs, spherical aberration, and coma aberration increased after small-incision lenticule extraction (P < .001 for total HOAs, spherical aberration; P = .004 for coma). At 6 months postoperatively, total HOAs and spherical aberration were significantly larger in the transepithelial PRK group than in the small-incision lenticule extraction group. Coma aberration was larger in the small-incision lenticule extraction group than in the transepithelial PRK group. Spherical aberration induction was significantly smaller in the small-incision lenticule extraction group than in the transepithelial PRK group (P < .001), and coma aberration induction was larger in the small-incision lenticule extraction group than in the transepithelial PRK group (P = .011).
Small-incision lenticule extraction demonstrated that the induction of total HOAs was comparable to corneal wavefront-guided transepithelial PRK, accompanied by smaller spherical aberration induction and larger coma aberration induction. During small-incision lenticule extraction, surgeons should aim to obtain optimum centration for smaller induction of corneal HOAs.
Lee H
，Yong Kang DS
，Reinstein DZ
，Arba-Mosquera S
，Kim EK
，Seo KY
，Kim TI
... -
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Comparison of objective and subjective visual quality after flapless laser vision correction for mild to moderate myopia: SMILE vs PRK.
To investigate the differences in surgical results and the objective and subjective quality of vision (QoV) of patients after small incision lenticule extraction (SMILE) versus alcohol-assisted photorefractive keratectomy (PRK).
Medical records of patients treated with SMILE and PRK were retrospectively examined. Visual quality, biometric parameters, Strehl ratio (SR), and corneal higher-order aberrations (HOAs) within a 6.0 mm area were recorded. The effective optical zone (EOZ) and decentration were measured using a tangential pre-post operation difference map. Subjective QoV and operation satisfaction were evaluated 6 months postoperatively using the Quality of Vision questionnaire.
The study comprised 100 eyes treated with SMILE (preoperative mean spherical equivalent (SE), - 4.52 ± 0.81 dioptres (D)) and 69 eyes with PRK (mean SE, - 4.21 ± 1.25 D). Six months postoperatively, the EOZ reduction was significantly larger in the PRK group (P < 0.001). Decentrations were comparable between the groups. Regarding visual symptoms, monocular diplopia was more common following PRK (P = 0.02), and 98 (98.00%) SMILE-treated and 67 (97.10%) PRK-treated patients were satisfied with the QoV. Both groups demonstrated significant increases in total HOAs, coma, and spherical aberration (SA) at 6 months postoperatively compared to preoperatively (P < 0.001); these values were significantly higher in the PRK (P < 0.05) compared to the SMILE group. SR increased significantly only in the PRK group (P < 0.05).
Although EOZ was more consistent with anticipated treatment and HOAs were fewer in SMILE, high patient-reported satisfaction and good corneal optical quality were achieved in both groups, indicating that both SMILE and alcohol-assisted PRK are excellent options for mild to moderate myopia correction.
Zhang R
，Zhang Y
，Yuan Y
，Chen Y
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