Journal of Refractive Surgery

Original Article 

Status of Residual Refractive Error, Ocular Aberrations, and Accommodation After Myopic LASIK, SMILE, and TransPRK

Naren Shetty, MD; Zelda Dadachanji, MD; Raghav Narasimhan, MTech; Gairik Kundu, MD; Pooja Khamar, MD; Prerna Ahuja, MD; Vijay Kumar, MOpt; Vikas Kumar, MOpt; Rohit Shetty, MD, PhD, FRCS; Rudy M.M.A. Nuijts, MD, PhD; Abhijit Sinha Roy, PhD

Abstract

PURPOSE:

To analyze residual refractive error, ocular aberrations, and visual acuity (VA) during accommodation simultaneously with ocular aberrometry in eyes after laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK).

METHODS:

Ocular aberrometry (Tracey Technologies, Houston, TX) was performed 3 months after LASIK (n = 95), SMILE (n = 73), and TransPRK (n = 35). While measuring the aberrations, VA was measured at distance (20 ft), intermediate (60 cm), and near (40 cm) targets. The examinations were done monocularly. A parallel group of age-matched normal eyes (n = 50) with 20/20 Snellen distance VA also underwent aberrometry.

RESULTS:

Distribution of residual spherical error of LASIK eyes matched the normal eyes the best, followed by SMILE and TransPRK. However, the distribution of cylindrical error of the SMILE eyes was distinctly different from the rest (P < .05). The SMILE eyes tended to be undercorrected by approximately 0.25 diopters (D) on average at all reading targets compared to LASIK eyes (P < .05). The undercorrection was greater when the magnitude of the preoperative cylinder exceeded 0.75 D (P < .05). The VA of LASIK and SMILE eyes was similar to normal eyes at all targets, but the TransPRK eyes were marginally inferior (P < .05). Only the ocular defocus changed differentially between the study groups during accommodation and the magnitude of change was least for TransPRK eyes (P < .05). However, postoperative near and intermediate accommodation of LASIK eyes were similar to normal eyes, followed by SMILE eyes and then TransPRK eyes.

CONCLUSIONS:

The refractive and aberrometric status of the LASIK eyes was closest to the normal eyes. The SMILE procedure may benefit from slight overcorrection of the preoperative refractive cylinder.

[J Refract Surg. 2019;35(10):624–631.]

Abstract

PURPOSE:

To analyze residual refractive error, ocular aberrations, and visual acuity (VA) during accommodation simultaneously with ocular aberrometry in eyes after laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK).

METHODS:

Ocular aberrometry (Tracey Technologies, Houston, TX) was performed 3 months after LASIK (n = 95), SMILE (n = 73), and TransPRK (n = 35). While measuring the aberrations, VA was measured at distance (20 ft), intermediate (60 cm), and near (40 cm) targets. The examinations were done monocularly. A parallel group of age-matched normal eyes (n = 50) with 20/20 Snellen distance VA also underwent aberrometry.

RESULTS:

Distribution of residual spherical error of LASIK eyes matched the normal eyes the best, followed by SMILE and TransPRK. However, the distribution of cylindrical error of the SMILE eyes was distinctly different from the rest (P < .05). The SMILE eyes tended to be undercorrected by approximately 0.25 diopters (D) on average at all reading targets compared to LASIK eyes (P < .05). The undercorrection was greater when the magnitude of the preoperative cylinder exceeded 0.75 D (P < .05). The VA of LASIK and SMILE eyes was similar to normal eyes at all targets, but the TransPRK eyes were marginally inferior (P < .05). Only the ocular defocus changed differentially between the study groups during accommodation and the magnitude of change was least for TransPRK eyes (P < .05). However, postoperative near and intermediate accommodation of LASIK eyes were similar to normal eyes, followed by SMILE eyes and then TransPRK eyes.

CONCLUSIONS:

The refractive and aberrometric status of the LASIK eyes was closest to the normal eyes. The SMILE procedure may benefit from slight overcorrection of the preoperative refractive cylinder.

[J Refract Surg. 2019;35(10):624–631.]

Accuracy of any refractive surgery technique has always been a subject of intense study. Among them, laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and photorefractive keratectomy (PRK) are the most commonly performed surgeries. Even with the latest LASIK platforms, the eyes may have some degree of residual refractive error, particularly cylindrical refractive error.1 If the discrepancy between the axis of refractive and corneal cylinder exceeds 20°, then the eyes have greater residual refractive error and inferior distance visual acuity after topography-guided LASIK.2 The residual refractive error and distance visual acuity after transepithelial PRK (TransPRK) are similar to the outcomes of femtosecond laser–assisted LASIK.3 Myopic regression in terms of subjective refraction is clinically insignificant after both LASIK and SMILE over a 5-year follow-up.4 However, undercorrection of astigmatism in SMILE compared to LASIK has been reported.5,6

Due to differences in the method of tissue ablation and some differences between treatment platforms, postoperative wound healing may differ between platforms. Therefore, the impact of these different procedures may cause a differential residual refractive error, ocular aberrations, and accommodation between the groups. Unfortunately, a single study to investigate these hypothesized differential outcomes between the procedures with a common measurement method is still lacking.

Ocular aberrometry can be an accurate tool for objective assessment of refractive error under real time visual acuity assessment.7 Therefore, the primary objective of this study was to assess the residual refractive error, residual astigmatism, and visual acuity at distance (20 ft), intermediate (60 cm), and near (40 cm) simultaneously using ocular wavefront aberrometry. This enabled precise determination of the magnitude of residual cylinder and its correlation with visual acuity at different reading targets. The secondary objective of this study was to assess the corresponding changes in ocular aberrations, specifically defocus and spherical aberration, measured simultaneously by the aberrometer.

Patients and Methods

This was a prospective, interventional, and longitudinal study. The study was approved by the ethics committee of Narayana Nethralaya Eye Hospital, Bangalore, India. The study adhered to the tenets of the Declaration of Helsinki. Inclusion criteria were stable refraction (less than −10.00 diopters [D] spherical equivalent refraction with astigmatism of not more than −3.00 D) for a period of 1 year (change less than 0.25 D). Patients with less than 480-µm central corneal thickness or a history of keratoconus, diabetes mellitus, collagen vascular disease, pregnancy, breast-feeding, and any prior ocular surgery or trauma were excluded from the surgery. In all eyes, the calculated residual stromal thickness was greater than 250 µm. All patients underwent subjective refractive error assessment (sphere, cylinder, and axis) preoperatively for planning of treatment. For SMILE and TransPRK, no nomogram adjustments to the subjective spherocylindrical error were made for moderate and high myopia. For LASIK, the adjustments were made based on the Wellington nomogram for different magnitudes of refractive error.

LASIK (wavefront optimized) was performed with the WaveLight FS200 femtosecond laser and Wave-Light EX500 excimer laser (Alcon Laboratories, Inc., Fort Worth, TX). The flap had a 9-mm diameter and 110-µm thickness. The optical zone diameter was 6 mm. SMILE was performed with the VisuMax femto-second laser (Carl Zeiss Meditec, Jena, Germany). The lenticule and cap diameter were 6 and 7.7 mm, respectively. The VisuMax laser energy was set to 160 nJ. In eyes with preoperative subjective cylinder in excess of −1.00 D, the horizontal and vertical meridian were marked prior to surgery to compensate for cyclotorsion. TransPRK was a single-step procedure, where both the epithelium and stroma were ablated by the Amaris 1,050-Hz excimer laser (SCHWIND eye-tech-solutions, Kleinostheim, Germany). The optical diameter was 6 mm. In TransPRK, the treatment zone size was determined by the laser software and only tissue within the treatment zone was removed by the laser. The target refraction for each eye was zero spherical and cylindrical error. A single surgeon (RS) performed all surgeries. The choice of the type of surgery was left to the patient after due counselling on the advantages and disadvantages of each surgery. All of the eyes were clinically eligible for any one of the three surgeries.

Postoperatively (3 months), all eyes underwent ocular aberrometry with the iTrace aberrometer (Tracey Technologies, Houston, TX) under monocular conditions. In front of the aberrometer, a distance (20 ft), intermediate (60 cm), and near (40 cm) visual acuity chart was kept for reading tests. While the aberrations were measured by the device, the patient was able to read through a hole in the center of the Placido console. Thus, the patient's eye was fixated at the letters on the chart and this provided a stable aberrometry measurement at each distance. While an eye was being tested, the other eye was covered with a patch and the internal fixation light of the device was turned off. For data analyses, the sphere, cylinder, and aberrations measured by the device were recalculated by choosing the minimum of the three pupil diameters measured at each distance. This ensured that the pupil diameter was not a confounder in the analyses of a given eye. Further, the aberrometry measurements were repeated at distance, near, and intermediate targets on a group of age-matched eyes having subjective distance visual acuity of 0.0 logMAR (Snellen 20/20). The inclusion criteria for these eyes were no prior ocular surgery, no existing systemic or ocular medications, no existing systemic or ocular diseases, no corneal degenerations, a clear lens, and clear ocular media. At all reading distances, the luminance was approximately 100 lux. The postoperative visual acuities, derived during the objective measurements with the iTrace, were uncorrected measures at distance, intermediate, and near. Only measurements that met the quality standard of the iTrace were used for statistical analyses.

Statistical Analyses

The data were assessed for normality of distribution with the Kolmogorov–Smirnov test. Only one eye per patient was chosen at random for analyses. Because some variables were non-parametric in distribution, all variables were reported as median with 95% confidence interval. For a given eye, the same pupil (analyses diameter) size was manually selected on the device to recalculate the Zernike aberrometric terms for distance, intermediate, and near. The visual acuities at all distances were converted to logMAR units. Among the ocular aberrations, the indices of interest were sphere (D), cylinder (D), defocus (µm), root mean square of coma (µm), spherical aberration (µm), and root mean square of lower order (LORMS; µm) and higher order (HORMS; µm) aberrations. For multi-group post-hoc comparisons, the Kruskal–Wallis test was used. A P value of less than .05 was considered statistically significant.

Results

Table 1 lists the preoperative demographics of the eyes. The median age of the normal patients was 25 ± 21.32 years. Preoperatively, the median age of patients who had TransPRK was significantly different from the rest (P < .001), but this difference was less than 2 years and not clinically significant. The uncorrected (UDVA) and corrected distance visual acuity were similar between the groups (P > .05). Preoperatively, the spherical error and spherical equivalent of the TransPRK eyes differed from the rest (P = .02). However, the cylindrical error of the SMILE eyes differed from the rest (P = .02). The central corneal thickness of the LASIK eyes was significantly greater than that of the SMILE and TransPRK eyes (P < .001).

Preoperative Demographics (Median With 95% Confidence Interval)

Table 1:

Preoperative Demographics (Median With 95% Confidence Interval)

Figure 1 shows the postoperative distribution of residual spherical error of the groups at all reading distances. At distance, the proportion of normal eyes within ±0.50 D was significantly greater than LASIK (P = .02) and SMILE (P = .01) eyes. At distance, the proportion of normal eyes within ±1.00 D was significantly greater than SMILE (P = .02) and TransPRK (P = .03) eyes. At intermediate, the proportion of normal eyes within ±0.50 D was significantly lower than SMILE (P = .02) and TransPRK (P = .003) eyes, and the proportion of normal eyes within ±1.00 D was significantly lower than TransPRK eyes (P = .048) only. At intermediate, the proportion of eyes with residual spherical error greater than −0.50 D was similar between the normal, LASIK, and SMILE eyes (P > .05), but differed significantly from the TransPRK eyes (P = .02). At near, the proportion of eyes within ±0.50 D was similar between all groups (P > .05), and the proportion of normal eyes within ±1.00 D was significantly greater than TransPRK eyes (P = .02) only. Overall, the proportion of eyes within the LASIK group matched the proportions within the normal eyes group the best, followed by SMILE and TransPRK.

The percentage distribution (y-axis) of postoperative residual spherical error measured by aberrometry in the normal, laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK) eyes at (A) distance (20 ft), (B) intermediate (60 cm), and (C) near (40 cm) target. The percentage distribution is indicated above the respective bar column. D = diopters

Figure 1.

The percentage distribution (y-axis) of postoperative residual spherical error measured by aberrometry in the normal, laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK) eyes at (A) distance (20 ft), (B) intermediate (60 cm), and (C) near (40 cm) target. The percentage distribution is indicated above the respective bar column. D = diopters

Figure 2 shows the postoperative distribution of residual cylindrical error of the groups at all reading distances. Interestingly, only the distribution of the SMILE eyes differed significantly from the distributions of the other eye groups (P < .05). Table 2 shows the median residual spherical error, residual cylindrical error, and corresponding visual acuities at distance, intermediate, and near for all groups. The spherical error of all groups at distance was similar (P = 1.00). At intermediate, the spherical error of the normal eyes differed significantly from the SMILE and TransPRK eyes (P < .02). At near, all groups differed significantly from each other (P < .0001). However, this difference between the median spherical error between the refractive groups was approximately 0.12 D for near (Table 2). At distance, the cylindrical error of the normal and LASIK eyes was significantly different than the SMILE eyes (P = .03). Additionally, the cylindrical error of the LASIK eyes differed significantly from the TransPRK eyes at both intermediate (P < .01) and near (P < .001). Interestingly, the visual acuity of the normal, LASIK, and SMILE eyes was clinically similar at near and intermediate except for the TransPRK eyes (P < .0001).

The percentage distribution (y-axis) of postoperative residual cylindrical error measured by aberrometry in the normal, laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK) eyes at (A) distance (20 ft), (B) intermediate (60 cm), and (C) near (40 cm) target. The percentage distribution is indicated above the respective bar column. D = diopters

Figure 2.

The percentage distribution (y-axis) of postoperative residual cylindrical error measured by aberrometry in the normal, laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and transepithelial photorefractive keratectomy (TransPRK) eyes at (A) distance (20 ft), (B) intermediate (60 cm), and (C) near (40 cm) target. The percentage distribution is indicated above the respective bar column. D = diopters

Postoperative Median (95% Confidence Interval) Spherical and Cylindrical Power at Near, Intermediate, and Distance Targets in LASIK (n = 95), SMILE (n = 73), and TransPRK (n = 35) Eyes Compared With Age-Matched Normal Eyes

Table 2:

Postoperative Median (95% Confidence Interval) Spherical and Cylindrical Power at Near, Intermediate, and Distance Targets in LASIK (n = 95), SMILE (n = 73), and TransPRK (n = 35) Eyes Compared With Age-Matched Normal Eyes

Table 3 shows the postoperative ocular aberrations at distance between groups. Only spherical aberration (P < .001) and LORMS (P = .01) differed statistically between the groups, although these differences were clinically small. From Figure 3A, only the change in defocus and LORMS was significantly different among all groups (P < .0001). The same was observed following accommodation from distance to near (Figure 3B). Among the SMILE eyes, an interesting observation was made (Figure 4). In eyes (n = 53) with preoperative subjective myopic cylinder of less than −0.75 D, the median cylinder decreased from −0.50 (−0.50, −0.50) to −0.25 (−0.37, −0.25) D (P = .75). In the remaining eyes, it decreased from −1.25 (−1.50, −1.04) to −0.81 (−0.62, 1.00) D (P < .001). Thus, the undercorrection of cylinder was greater with a higher magnitude of preoperative cylinder. In LASIK eyes with preoperative subjective cylinder of greater than −0.75 D, the median cylinder decreased from −1.25 (−1.23, −1.75) to −0.37 (−0.36, −0.62) D (P < .001). In eyes with a myopic cylinder of less than −0.75 D, the median cylinder decreased from −0.50 (−0.50, −0.50) to −0.37 (−0.37, −0.50) D (P = .81). Thus, the LASIK eyes had a significantly lower magnitude of undercorrection than SMILE eyes (Figure 4).

Postoperative Ocular Aberrations at Distance (20 ft)

Table 3:

Postoperative Ocular Aberrations at Distance (20 ft)

Change (accommodated minus distance) in ocular defocus and root mean square of lower order aberrations (LORMS) at: (A) intermediate and (B) near target. The median with 95% confidence interval is indicated above the respective bar column. The y-axis is the magnitude of the change in microns. LASIK = laser-assisted in situ keratomileusis; SMILE = small incision lenticule extraction; TransPRK = transepithelial photorefractive keratectomy

Figure 3.

Change (accommodated minus distance) in ocular defocus and root mean square of lower order aberrations (LORMS) at: (A) intermediate and (B) near target. The median with 95% confidence interval is indicated above the respective bar column. The y-axis is the magnitude of the change in microns. LASIK = laser-assisted in situ keratomileusis; SMILE = small incision lenticule extraction; TransPRK = transepithelial photorefractive keratectomy

Median residual cylinder in the small incision lenticule extraction (SMILE) and laser-assisted in situ keratomileusis (LASIK) eyes preoperatively (preop) and postoperatively (postop) segregated into two groups. In one group, all eyes had a cylinder greater than −0.75 diopters (D). In the other, all had a cylinder of less than −0.75 D.

Figure 4.

Median residual cylinder in the small incision lenticule extraction (SMILE) and laser-assisted in situ keratomileusis (LASIK) eyes preoperatively (preop) and postoperatively (postop) segregated into two groups. In one group, all eyes had a cylinder greater than −0.75 diopters (D). In the other, all had a cylinder of less than −0.75 D.

Discussion

Some degree of residual refractive error typically exists after myopic refractive surgery. Because refractive surgery alters the corneal surface, the accommodation of the eye after surgery may also be affected. However, a simultaneous assessment of both accommodation and ocular aberrations is lacking in the literature. A recent study showed that ocular aberrometry can be an accurate tool to measure refractive error of an eye.7 The following were the key outcomes of the current study:

  1. The distribution of residual spherical and cylindrical error of the LASIK eyes was the closest to the age-matched normal eyes. The SMILE and TransPRK eyes were different and were further away from the distributions of the normal eyes. However, the SMILE and LASIK eyes had the greatest and smallest residual cylinder after surgery, independent of accommodation (Table 2).

  2. A similar response was observed during accommodation between the normal and LASIK eyes. Only ocular defocus changed during accommodation and the LASIK eyes were again closest to the normal eyes, followed by the SMILE eyes.

  3. There was a consistent difference of approximately 0.25 D between the SMILE and LASIK eyes at all reading targets (Table 2). This difference increased when the myopic preoperative cylinder was greater than −0.75 D (Figure 4).

  4. Despite the above differences, the visual acuity at all distances was similar between the LASIK, SMILE, and normal eyes. The TransPRK eyes had inferior near and intermediate visual acuity. This was similar to the trends seen with refractive error and ocular aberrations, where the TransPRK eyes differed the most from the other groups.

For all reading distances, the SMILE eyes may benefit from further overcorrection of the preoperative cylinder by 0.25 D. These results have important implications for prospective presbyopia treatments on the anterior corneal surface because the postoperative accommodative response of the LASIK eyes was different from the SMILE and TransPRK eyes. Thus, the same nomograms cannot be used between them. Further, the TransPRK ablation profile or programmed refractive error may require further modifications to compensate for the inferior near and intermediate visual acuity in the acute postoperative phase. These aspects required further study.

In a recent study on wavefront-optimized LASIK, the residual spherical and cylindrical error was 0.06 ± 0.23 and −0.33 ± 0.14 D, respectively.1 Further, the UDVA was 20/20 or better in 92% of the eyes.1 In eyes with myopia of less than −3.00 D, the UDVA was 20/20 or better in 87% of the eyes.8 Further, 72.4% and 93.1% of the eyes were within ±0.50 and ±1.00 D of residual spherical equivalent, respectively.8 In eyes having myopia between −3.00 and −6.00 D, the UDVA was 20/20 or better in 89.7% of the eyes.8 In terms of residual cylinder, 65.5% and 93.1% of the eyes were within ±0.50 and ±1.00 D, respectively.8 In another study, residual cylinder was within ±0.50 and ±1.00 D in 77.1% and 100% of the eyes, respectively.9 Further, the UDVA was 20/20 or better in approximately 85.71% of the eyes.9 Thus, our LASIK results were in agreement with the latest reported outcomes for the wavefront-optimized platform. The long-term (5 years) results of SMILE in myopic eyes (less than −6.00 D) indicated that 93% and 100% of the eyes were within ±0.50 and ±1.00 D of the intended correction, respectively.10 Further, the spherical equivalent was within ±0.50 D in 98% of the eyes.10 Another long-term study (3-year follow-up) on SMILE outcomes (moderate to high myopia) showed that 80% of the eyes were within ±0.50 D of the attempted spherical equivalent and the UDVA was 20/20 or better in 90% of the eyes.11

Some recent studies reported undercorrection of refractive error in SMILE eyes. The eyes having with-the-rule astigmatism had a significant undercorrection of cylinder when the preoperative cylinder increased beyond 2.00 D.11 With against-the-rule astigmatism, the undercorrection of cylinder was not affected by the magnitude of preoperative cylinder.11 Another study confirmed that the undercorrection was present in eyes with preoperative cylinder greater than 1.50 D having with-the-rule (median magnitude of error was −0.30 D) astigmatism.1 Other studies also reported significant undercorrection in SMILE eyes.12,13 For cylinder, the mean magnitude of error was −0.07 ± 0.20 and −0.20 ± 0.35 in the wavefront-guided LASIK and SMILE eyes, respectively (P = .012).13 The results from this study also show the same trends, particularly in eyes with a preoperative myopic cylinder greater than 0.75 D. However, this undercorrection remained unchanged during accommodation. Further, the greater residual cylinder possibly enabled both the LASIK and SMILE eyes to achieve similar near and intermediate visual acuity as the normal eyes.14

In TransPRK, the laser removed both the epithelium and stroma. Tables 12 clearly show that TransPRK achieved good clinical outcomes. In fact, the residual cylinder distribution in TransPRK eyes was better than the SMILE eyes but inferior to the LASIK and normal eyes (Figure 2). In one study, the magnitude of error was less than −0.25 D and 100% of the eyes achieved UDVA of 20/20 or better postoperatively.15 In a recent study, 100% of the eyes achieved a postoperative cylinder within ±0.50 D and postoperative UDVA of 20/20 or better in 100% of the eyes.16 In another study, the postoperative spherical equivalent was within ±0.50 D in 100% of the eyes after TransPRK.16 Our visual acuity outcomes at distance matched the outcomes of these earlier studies. However, the residual cylinder tended to be greater. In one study, an induction of an optimum magnitude of negative spherical aberration resulted in better near visual acuity in presbyopic eyes.17 However, there was no change in ocular spherical aberration during accommodation in any of the study groups. It is possible that these younger TransPRK eyes may have had ongoing epithelial thickness changes and required a longer time for adaption to the new corneal shape. Hence, this finding requires further study with longer follow-up. Thus, the current study revealed novel accommodative differences between the three surgeries and correlated the findings to visual acuity and ocular aberrations. This methodology of ocular aberrometry could be used to understand the visual optics postoperatively, even in customized platforms such as topography-guided LASIK.2

References

  1. Ozulken K, Yuksel E, Tekin K, Kiziltoprak H, Aydogan S. Comparison of wavefront-optimized ablation and topography-guided Contoura ablation with LYRA protocol in LASIK. J Refract Surg. 2019;35(4):222–229. https://doi.org/10.3928/1081597X-20190304-02 PMID: doi:10.3928/1081597X-20190304-02 [CrossRef]30984979
  2. Wallerstein A, Gauvin M, Qi SR, Bashour M, Cohen M. Primary topography-guided LASIK: treating manifest refractive astigmatism versus topography-measured anterior corneal astigmatism. J Refract Surg. 2019;35(1):15–23. https://doi.org/10.3928/1081597X-20181113-01 PMID: doi:10.3928/1081597X-20181113-01 [CrossRef]30633783
  3. Luger MH, Ewering T, Arba-Mosquera S. Myopia correction with transepithelial photorefractive keratectomy versus femtosecond-assisted laser in situ keratomileusis: one-year case-matched analysis. J Cataract Refract Surg. 2016;42(11):1579–1587. https://doi.org/10.1016/j.jcrs.2016.08.025 PMID: doi:10.1016/j.jcrs.2016.08.025 [CrossRef]27956284
  4. Li M, Li M, Chen Y, et al. Five-year results of small incision lenticule extraction (SMILE) and femtosecond laser LASIK (FSLASIK) for myopia. Acta Ophthalmol. 2019;97(3):e373–e380. https://doi.org/10.1111/aos.14017 PMID: doi:10.1111/aos.14017 [CrossRef]30632671
  5. 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(4):553–559. https://doi.org/10.1136/bjophthalmol-2015-307238 PMID: doi:10.1136/bjophthalmol-2015-307238 [CrossRef]
  6. Pérez-Izquierdo R, Rodríguez-Vallejo M, Matamoros A, et al. Influence of preoperative astigmatism type and magnitude on the effectiveness of SMILE correction. J Refract Surg. 2019;35(1):40–47. https://doi.org/10.3928/1081597X-20181127-01 PMID: doi:10.3928/1081597X-20181127-01 [CrossRef]30633786
  7. Carracedo G, Carpena-Torres C, Serramito M, Batres-Valderas L, Gonzalez-Bergaz A. Comparison between aberrometry-based binocular refraction and subjective refraction. Transl Vis Sci Technol. 2018;7(4):11. https://doi.org/10.1167/tvst.7.4.11 PMID: doi:10.1167/tvst.7.4.11 [CrossRef]30087806
  8. Khalifa MA, Alsahn MF, Shaheen MS, Pinero DP. Comparative analysis of the efficacy of astigmatic correction after wavefront-guided and wavefront-optimized LASIK in low and moderate myopic eyes. Int J Ophthalmol. 2017;10(2):285–292. PMID:28251090
  9. Jain AK, Malhotra C, Pasari A, Kumar P, Moshirfar M. Outcomes of topography-guided versus wavefront-optimized laser in situ keratomileusis for myopia in virgin eyes. J Cataract Refract Surg. 2016;42(9):1302–1311. https://doi.org/10.1016/j.jcrs.2016.06.035 PMID: doi:10.1016/j.jcrs.2016.06.035 [CrossRef]27697248
  10. Agca A, Tülü B, Yasa D, Yildirim Y, Yildiz BK, Demirok A. Long-term (5 years) follow-up of small-incision lenticule extraction in mild-to-moderate myopia. J Cataract Refract Surg. 2019;45(4):421–426. https://doi.org/10.1016/j.jcrs.2018.11.010 PMID: doi:10.1016/j.jcrs.2018.11.010 [CrossRef]30709628
  11. Han T, Xu Y, Han X, et al. Three-year outcomes of small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism. Br J Ophthalmol. 2019;103(4):565–568. https://doi.org/10.1136/bjophthalmol-2018-312140 PMID: doi:10.1136/bjophthalmol-2018-312140 [CrossRef]
  12. Zhang J, Wang Y, Wu W, Xu L, Li X, Dou R. Vector analysis of low to moderate astigmatism with small incision lenticule extraction (SMILE): results of a 1-year follow-up. BMC Ophthalmol. 2015;15(1):8. https://doi.org/10.1186/1471-2415-15-8 PMID: doi:10.1186/1471-2415-15-8 [CrossRef]25618419
  13. Khalifa MA, Ghoneim AM, Shaheen MS, Piñero DP. Vector analysis of astigmatic changes after small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis. J Cataract Refract Surg. 2017;43(6):819–824. https://doi.org/10.1016/j.jcrs.2017.03.033 PMID: doi:10.1016/j.jcrs.2017.03.033 [CrossRef]28732617
  14. Leube A, Ohlendorf A, Wahl S. The influence of induced astigmatism on the depth of focus. Optom Vis Sci. 2016;93(10):1228–1234. https://doi.org/10.1097/OPX.0000000000000961 PMID: doi:10.1097/OPX.0000000000000961 [CrossRef]27536975
  15. Jun I, Yong Kang DS, Arba-Mosquera S, et al. Clinical outcomes of mechanical and transepithelial photorefractive keratectomy in low myopia with a large ablation zone. J Cataract Refract Surg. 2019;45(7):977–984. https://doi.org/10.1016/j.jcrs.2019.02.007 PMID: doi:10.1016/j.jcrs.2019.02.007 [CrossRef]31029476
  16. Jun I, Kang DSY, Arba-Mosquera S, Kim EK, Seo KY, Kim TI. Clinical outcomes of transepithelial photorefractive keratectomy according to epithelial thickness. J Refract Surg. 2018;34(8):533–540. https://doi.org/10.3928/1081597X-20180618-02 PMID: doi:10.3928/1081597X-20180618-02 [CrossRef]30089183
  17. Shetty N, Kochar S, Paritekar P, et al. Patient-specific determination of change in ocular spherical aberration to improve near and intermediate visual acuity of presbyopic eyes. J Biophotonics. 2019;12(4):e201800259. https://doi.org/10.1002/jbio.201800259 PMID: doi:10.1002/jbio.201800259 [CrossRef]

Preoperative Demographics (Median With 95% Confidence Interval)

CharacteristicLASIKSMILETransPRKP
Age (years)24 (19, 33)26 (20, 34)24 (20, 32)< .001
Sphere (D)−4.50 (−10.50, −0.75)−4.75 (−10.00, −1.25)−3.00 (−8.25, 1.00).02
Cylinder (D)−0.75 (−3.50, 0.00)−0.50 (−2.50, 0.00)−0.50 (−0.25, 0.25).02
SE (D)−4.69 (−11.50, −1.25)−5.13 (−10.75, −1.38)−3.25 (−9.00, 0.75).02
CCT (µm)539 (534, 544)521 (517, 524)516 (508, 541)< .001
UDVA (logMAR)1.3 (1.3, 1.3)1.18 (1, 1.3)1.3 (1, 1.3).32
CDVA (logMAR)0 (0, 0)0 (0, 0)0 (0, 0).18

Postoperative Median (95% Confidence Interval) Spherical and Cylindrical Power at Near, Intermediate, and Distance Targets in LASIK (n = 95), SMILE (n = 73), and TransPRK (n = 35) Eyes Compared With Age-Matched Normal Eyes

GroupDistanceIntermediateNear
Spherical error (D)
  Normal0.12 (0.12, 0.25)−1.00 (−1.12, −1.00)−1.87 (−2.00, −1.75)
  LASIK−0.25 (−0.37, −0.12)−1.00 (−1.00, −0.87)−1.62 (−1.75, −1.50)
  SMILE0.00 (−0.25, 0.25)−0.87 (−1.00, −0.75)−1.50 (−1.62, −1.25)
  TransPRK−0.25 (−0.40, 0.00)−0.87 (−0.90, −0.75)−1.37 (−1.54, −1.25)
   P< .0001.02< .0001
Cylindrical error (D)
  Normal−0.44 (−0.62, −0.37)−0.50 (−0.50, −0.37)−0.50 (−0.62, −0.32)
  LASIK−0.37 (−0.50, −0.37)−0.37 (−0.50, −0.37)−0.37 (−0.50, −0.37)
  SMILE−0.62 (−0.75, −0.50)−0.62 (−0.72, −0.50)−0.62 (−0.75, −0.62)
  TransPRK−0.50 (−0.62, −0.37)−0.50 (−0.62, −0.50)−0.50 (−0.62, −0.37)
   P.03< .01< .001
Visual acuity (logMAR)
  Normal0 (0, 0)−0.04 (−0.08, −0.04)0 (0, 0)
  LASIK0 (0, 0)0.02 (0.02, 0.02)0 (0, 0)
  SMILE0 (0, 0)0.02 (0.02, 0.12)0 (0, 0.1)
  TransPRK0 (0, 0)0.22 (0.12, 0.22)0.18 (0.1, 0.2)
   P1.00< .0001< .0001

Postoperative Ocular Aberrations at Distance (20 ft)

AberrationNormalLASIKSMILETransPRKP
Defocus (µm)0.01 (−0.03, 0.08)0.06 (0.04, 0.11)0.10 (0.00, 0.15)0.03 (−0.05, 0.17).74
Coma RMS (µm)0.08 (0.06, 0.10)0.09 (0.08, 0.10)0.11 (0.10, 0.13)0.09 (0.07, 0.12).15
Spherical aberration (µm)0.01 (0.00, 0.02)−0.01 (−0.02, 0)−0.02 (−0.03, −0.01)0.00 (−0.02, 0.01)< .001
LORMS (µm)0.20 (0.16, 0.24)0.28 (0.23, 0.32)0.34 (0.28, 0.42)0.32 (0.20, 0.42).01
HORMS (µm)0.1 (0.08, 0.13)0.13 (0.11, 0.14)0.15 (0.13, 0.17)0.11 (0.09, 0.16).03
Authors

From the Department of Cornea and Refractive Surgery, Narayana Nethralaya Eye Hospital, Bangalore, India (NS, ZD, GK, PK, PA, Vikas Kumar, Vijay Kumar, RS); Imaging, Biomechanics and Mathematical Modeling Solutions Lab, Narayana Nethralaya Foundation, Bangalore, India (RN, ASR); and the Department of Ophthalmology, Maastricht University Medical Center, Maastricht, The Netherlands (RMMAN).

Dr. Nuijts is a consultant for Alcon, Asico, Chiesi, and Theapharma, and a speaker for Abbott, Alcon, Bausch & Lomb, Carl Zeiss, Chiesi, HumanOptics, Ophtec, Oculentis, and Gebauer. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (RS, RMMAN, ASR); data collection (NS, ZD, RN, GK, PK, Vijay Kumar, Vikas Kumar); analysis and interpretation of data (NS, ZD, RN, PK, PA); writing the manuscript (NS, ZD, RN, GK, PK, PA, Vijay Kumar, Vikas Kumar, ASR); critical revision of the manuscript (RS, RMMAN, ASR); statistical expertise (ASR), administrative, technical, or material support (NS, ZD, RN, GK, PK, PA)

Correspondence: Abhijit Sinha Roy, PhD, Narayana Nethralaya, #258/A Hosur Road, Bommasandra, Bangalore 560099, India. E-mail: asroy27@yahoo.com

Received: May 28, 2019
Accepted: September 16, 2019

10.3928/1081597X-20190916-02

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