LASIK ablation centration: an objective digitized assessment and comparison between two generations of an excimer laser

Digital Pupillometry and Centroid Shift Changes in Dominant and Nondominant Eyes

PURPOSE

To investigate the differences between dominant and nondominant eyes in a predominantly young patient population by analyzing the angle kappa, pupil size, and center position in dominant and nondominant eyes.

METHODS

A total of 126 young college students (252 eyes) with myopia who underwent femtosecond laser-combined LASIK were randomly selected. Ocular dominance was determined using the hole-in-card test. The WaveLight Allegro Topolyzer (WaveLight Laser Technologies AG, Erlangen, Germany) was used to measure the pupil size and center position. The offset between the pupil center and the coaxially sighted corneal light reflex (P-Dist) of the patients was recorded by the x- and y-axis eyeball tracking adjustment program of the WaveLight Eagle Vision EX500 excimer laser system (Wavelight GmbH). The patient's vision (uncorrected distance visual acuity [UDVA], best-corrected visual acuity (BCVA), and refractive power (spherical equivalent, SE) were observed preoperatively, 1 week, 4 weeks, and 12 weeks postoperatively, and a quality of vision (QoV) questionnaire was completed.

RESULTS

Ocular dominance occurred predominantly in the right eye [right vs. left: (178) 70.63% vs. (74) 29.37%; p < 0.001]. The P-Dist was 0.202 ± 0.095 mm in the dominant eye and 0.215 ± 0.103 mm in the nondominant eye (p = 0.021). The horizontal pupil shift was - 0.07 ± 0.14 mm in dominant eyes and 0.01 ± 0.13 mm in nondominant eyes (p = 0.001) (the temporal displacement of the dominant eye under mesopic conditions). The SE was negatively correlated with the P-Dist (r = - 0.223, p = 0.012 for the dominant eye and r = - 0.199, p = 0.025 for the nondominant eye). At 12 weeks postoperatively, the safety index (postoperative BDVA/preoperative BDVA) of the dominant and nondominant eyes was 1.20 (1.00, 1.22) and 1.20 (1.00, 1.20), respectively, and the efficacy index (postoperative UDVA/preoperative BDVA) was 1.00 (1.00, 1.20) and 1.00 (1.00, 1.20), respectively; the proportion of residual SE within ± 0.50 D was 98 and 100%, respectively.

CONCLUSIONS

This study found that ocular dominance occurred predominantly in the right eye. The pupil size change was larger in the dominant eye. The angle kappa of the dominant eye was smaller than that of the nondominant eye and the pupil center of the dominant eye was slightly shifted to the temporal side under mesopic conditions. The correction of myopia in the dominant and nondominant eyes exhibits good safety, efficacy, and predictability in the short term after surgery, and has good subjective visual quality performance after correction. We suggest adjusting the angle kappa percentage in the dominant eye to be lower than that of the nondominant eye in individualized corneal refractive surgery in order to find the ablation center closest to the visual axis.

Effect of preoperative pupil offset on corneal higher-order aberrations after femtosecond laser-assisted in situ keratomileusis

BACKGROUND

This study aimed to investigate the relationship between multiple higher-order aberrations (HOAs) subgroups and pupil offset, as well as to analyze the factors affecting postoperative corneal HOAs in patients with different degrees of refractive errors.

METHODS

We enrolled 160 patients (316 eyes) aged ≥ 18 years who had undergone femtosecond laser-assisted in situ keratomileusis (FS-LASIK) treatment. Based on the relationship between the preoperative pupil offset and the postoperative ΔHOAs, all patients were divided into two groups: group I (pupil offset ≤ 0.20 mm) and group II (pupil offset > 0.20 mm). All of the eyes had low to high myopia with or without astigmatism (manifest refraction spherical equivalent (MRSE) < -10.00 D). Uncorrected distance visual acuity, corrected distance visual acuity, MRSE, pupil offset, central corneal thickness, corneal HOAs, vertical coma (Z₃^-1), horizontal coma (Z₃¹), spherical aberration (Z₄⁰), trefoil 0° (Z₃³), and trefoil 30° (Z₃^-3) over a 6 mm diameter central corneal zone diameter were evaluated preoperatively and at 1 and 3 months postoperatively.

RESULTS

Our result revealed significant differences in postoperative corneal total root mean square (RMS) HOAs, RMS vertical coma, RMS horizontal coma, RMS spherical aberration, and RMS trefoil 30° between group I and group II. ΔMRSE was found to be an effective factor for ΔRMS HOAs (R² = 0.383), ΔRMS horizontal coma (R² = 0.205), and ΔRMS spherical aberration (R² = 0.397). In group II, multiple linear regression analysis revealed a significant correlation between preoperative pupillary offset and Δtotal RMS HOAs (R² = 0.461), ΔRMS horizontal coma (R² = 0.040), and ΔRMS trefoil 30°(R² = 0.089). The ΔRMS vertical coma effect factor is the Y-component, and the factor influencing ΔRMS spherical aberration was ΔMRSE (R² = 0.256).

CONCLUSION

A small pupil offset was associated with a lower induction of postoperative corneal HOAs. Efforts to optimize centration are critical for improving surgical outcomes in patients with FS-LASIK.

Characteristics of Pupil Offset in Young Asian Adults With Mild-Moderate and High Myopia

Purpose

The purpose of this study was to explore the characteristics of pupil offset in young Asian adults with myopia.

Methods

In total, 1200 eyes (600 young adults, 18–35 years old) were divided into mild-moderate and high groups according to equivalent spherical diopters (SEQ). The pupil offset and its X and Y components were compared between the groups. Linear correlation was analyzed among pupil offset, X and Y components, and SEQ. Multiple linear regression analysis was conducted for pupil offset and eye parameters.

Results

The mean age of all subjects was 22.5 ± 4.8 years. The mean magnitude of the pupil offset (0.18 ± 0.09 mm vs. 0.15 ± 0.08 mm) and Y component (0.12 ± 0.08 mm vs. 0.10 ± 0.07 mm) were larger in the high group than in the mild-moderate group (P < 0.05). The magnitude of pupil offset, X and Y components, and SEQ were positively correlated. The pupil center (PC) of the right eye in the mild-moderate group was mainly superotemporal to the corneal vertex and mainly superonasal for the left eye and both eyes in the high group. Multiple linear regression analysis revealed that the magnitude of pupil offset correlated with central corneal thickness, intraocular pressure, and mean corneal curvature (P < 0.05).

Conclusions

The magnitude of the pupil offset that correlated with partial eye parameters and its X and Y components increased as the SEQ increased, and the PC gradually shifted toward the superonasal direction in young Asian adults with myopia.

Translational Relevance

Subjects with high myopia with a larger pupil offset should be considered for better postoperative visual quality during refractive surgery.

Comparison of effective corneal refractive centration to the visual axis: LASIK vs. SMILE, a contralateral eye digitized comparison of the postoperative result

PURPOSE

To define and compare the centration of the ablation effect in LASIK to the corresponding effect in SMILE, in myopic laser vision correction in order to possibly explain the refractive performance differences noted between the two procedures in a contralateral eye study.

SETTING

Private Ambulatory Eye Surgery Unit.

DESIGN

Prospective randomized contralateral eye study.

METHODS

In 22 consecutive patients (44 eyes), one eye was prospectively randomized to have myopic topography-guided LASIK treatment and the contralateral eye to have SMILE; Digital image analysis of the achieved centration to the aimed corneal vertex was assessed for both procedures on the perioperative Scheimpflug tangential curvature maps, using a proprietary digitized methodology.

RESULTS

The radial displacement between the attempted centration on the corneal vertex versus the center of the effective anterior corneal curvature flattening was on average 130 ± 62 μm in the LASIK group and 313 ± 144μm in the SMILE group (P<0.001).

CONCLUSIONS

In this contralateral eye study, topography-guided myopic LASIK was found to achieve significantly better effective centration compared to myopic SMILE, in regards digitally measured decentration of the effective refractive change achieved in the anterior corneal curvature from the corneal vertex. This may explain the previously reported superior visual outcomes in the LASIK group eyes when compared to the contralateral SMILE group eyes.

Correlation Analysis of Refractive and Visual Quality after Wavefront-Optimized Laser In Situ Keratomileusis for 50% and 100% Angle Kappa Compensation

Purpose

To analyze the distribution of the offset between the pupil center and the coaxially sighted corneal light reflex (P-Dist), the effects of 50% and 100% angle kappa adjustments on refractive and visual quality in patients with moderate myopia were investigated.

Methods

A randomly selected 254 patients (254 eyes) with moderate myopia who underwent femtosecond laser-combined LASIK were examined. During the operation, the P-Dist of the patients was recorded by the x- and y-axis eyeball-tracking adjustment program of the WaveLight Eagle Vision EX500 excimer laser system. Preoperatively and 3 months postoperatively, the WaveLight® ALLEGRO Topolyzer was used to measure the pupil size and center position, and the wavefront sensor was used to measure the wavefront aberrations. The visual function tester (OPTEC 6500) measured contrast sensitivity.

Results

The average P-Dist was 0.220 ± 0.102 mm. When the P-Dist >0.220 mm, the postoperative residual cylinder was 0.29 ± 0.34 D in the group with the 50% adjustment and 0.40 ± 0.32 D in the 100% group, which was significantly higher than the 50% group (P=0.036). The coma was 0.21 ± 0.17 μm in the 50% adjusted group and 0.34 ± 0.25 μm in the 100% group, which was significantly higher than that in the 50% group (P=0.021). At the 1.5 c/d spatial frequency, contrast sensitivity in the adjusted 100% group was significantly lower than that in the 50% group under visual glare conditions (P=0.039).

Conclusion

The postoperative visual acuity and spherical equivalent were not affected in the two groups. However, when P-Dist >0.220 mm, the residual astigmatism and coma were lower in the 50% group. Individualized operations for those with moderate myopia and large-angle kappa in which 100% adjustment is chosen may not result in a better visual quality effect than 50%.

Scheimpflug vs Scanning-Slit Corneal Tomography: Comparison of Corneal and Anterior Chamber Tomography Indices for Repeatability and Agreement in Healthy Eyes

Purpose

To evaluate and compare the repeatability and agreement of Scheimpflug vs scanning-slit tomography of the cornea and the anterior chamber in terms of keratometric and tomographic indices in healthy eyes.

Methods

The 20 eyes of 10 healthy participants underwent 3 consecutive measurements using both Scheimpflug-tomography and scanning-slit tomography, diagnostic devices. Multiple corneal and anterior chamber tomographic parameters were recorded and evaluated to include corneal keratometry and its axis; corneal best-fit sphere (BFS), pachymetry mapping, angle kappa, anterior chamber depth (ACD), pupil diameter, and location. Repeatability for each device was assessed using the within each subject standard deviation of sequential exams, the coefficient variation (CV) and the intraclass correlation coefficient (ICC). Agreement between the two devices was assessed using Bland-Altman plots with 95% limits of agreement (LoA) and correlation coefficient (r).

Results

Both devices were found to have high repeatability (ICC>0.9) both in keratometric and other tomographic measurements. Scheimpflug tomography's repeatability though appeared superior in the average keratometry values, anterior and posterior BFS, thinnest corneal pachymetry value and location (p<0.05). Agreement: Statistically significant inter-device differences were noted in the mean values of K1, K2, BFS, ACD and thinnest corneal pachymetry (p<0.05). Despite the agreement differences noted, the two devices were well correlated (r>0.8) in respective measurements with Scheimpflug delivering consistently lower values than the scanning-slit tomography device.

Conclusion

Scheimpflug-tomography repeatability was found to be superior to that of scanning-slit tomography in this specific study, in most parameters evaluated. Inter-device agreement evaluation suggests that reading from the two devices may not be used interchangeably in absolute values, yet they are well correlated with Scheimpflug delivering consistently lower values in most.

Combined Phototherapeutic Keratectomy and Peripheral Anterior Stromal Puncture for the Treatment of Recurrent Corneal Erosion Syndrome

PURPOSE

To investigate the efficacy of the combined phototherapeutic keratectomy (PTK) and peripheral anterior stromal puncture (ASP) compared with that of PTK alone in patients with recurrent corneal erosion syndrome (RCES).

METHODS

The medical records of 25 patients (25 eyes) who underwent combined treatment of PTK and peripheral ASP for RCES from March 2016 to May 2017 were retrospectively reviewed. Twenty-three patients (23 eyes) treated with PTK alone from March 2015 to February 2016 served as a control group. All surgeries were performed by a single surgeon. This retrospective clinical study comprised 48 patients (48 eyes) who were followed up for more than 18 months. Clinical records of age, sex, laterality, etiology of RCES, and history of recurrence after treatment were evaluated.

RESULTS

Twenty-five eyes were treated with combined PTK and ASP, and 23 eyes were treated with PTK only. The mean follow-up period was 19.63 ± 2.97 and 19.75 ± 6.83 months, respectively. There were no differences in baseline parameters between the groups. In the combined treatment group, one patient experienced recurrence 6 months after the surgery. In the single treatment group, five patients showed recurrence at 4, 7, 8, 11, and 13 months after the surgery, respectively. Compared to the single treatment group, the combined treatment group showed significantly lower recurrence rate (p < 0.05). All recurred patients required no additional treatment except temporary therapeutic contact lenses and topical lubricants.

CONCLUSIONS

Our findings suggest that combined treatment of PTK and peripheral ASP is effective in alleviation of symptoms and prevention of recurrence in refractory RCES compared with treatment using PTK alone.

Clinical outcomes of corneal refractive surgery comparing centration on the corneal vertex with the pupil center: a meta-analysis

PURPOSE

To compare the visual and refractive outcomes between centration on the corneal vertex and the pupil center in corneal refractive surgery.

METHODS

A comprehensive literature search was conducted using PubMed, MEDLINE, EMBASE, and the Cochrane Library to identify relevant studies. The primary outcomes were the postoperative spherical equivalent (SE), effectiveness [uncorrected distance visual acuity (UDVA) ≥ 20/20, eyes within ± 0.50 diopter (D) of target refraction], and safety [loss ≥ 2 lines of corrected distance visual acuity (CDVA)]. Higher-order aberrations were considered secondary outcomes.

RESULTS

Seven studies describing a total of 1964 eyes were included in this meta-analysis. A statistical significance in postoperative SE was found between the two centration methods for the correction of myopia that favor the CV-centered method (p < 0.001). No significant differences were observed in the proportion of eyes with UDVA ≥ 20/20 or loss ≥ 2 lines of CDVA postoperatively. However, the proportion of eyes within ± 0.50 D was slightly higher (p = 0.02) and the coma aberration was much lower in the corneal vertex-centered method (p < 0.001).

CONCLUSION

Preferable visual and refractive outcomes could be achieved with either centering on the corneal vertex or pupil center in corneal refractive surgery; however, the corneal vertex-centered method has shown partial benefits in some clinical indices. In order to obtain higher quality of clinical evidences, more randomized controlled trials (RCTs) are required in further investigations.

Cylinder Axis Agreement: Unexpected Scenarios

Background

The purpose of this retrospective study was to evaluate cylinder axis agreement between manifest refraction (MR), cycloplegic refraction (CR), Allegro Oculyzer ІІ and Allegro Topolyzer-Vario.

Methods

We included 82 patients (32 males and 50 females, 28.1 ± 8.7 years old), with 156 eyes scheduled for wavefront optimized laser refractive surgery, photorefractive keratectomy (PRK) in 50 eyes and laser-assisted in situ keratomileusis (LASIK) in 106 eyes, for correction of simple, myopic, hyperopic or mixed astigmatism. Cylinder axis was determined under manifest and cycloplegic refractions and using Allegro Occulyzer ІІ and Allegro Topolyzer-Vario platforms. Cylinder axis agreement was assessed by intraclass correlation coefficient, Pearson correlation coefficient and by the method described by Bland and Altman.

Results

Intraclass correlation coefficient and Pearson correlation coefficient showed statistically significant cylinder axis agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario (p <0.001). Despite statistically significant cylinder axis agreement between the four measuring tools, 4 of 156 eyes (2.5%) showed unexpected discrepancy between Allegro Oculyzer ІІ and Allegro Topolyzer-Vario cylinder axis.

Conclusion

Although cylinder axis shows statistically significant agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario, unexpected discrepancies occur.

Functional Optical Zone and Centration Following SMILE and LASIK: A Prospective, Randomized, Contralateral Eye Study

PURPOSE

To compare centration and functional optical zone (FOZ) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (LASIK).

METHODS

In this prospective, randomized, single-masked, paired-eyed, clinical trial, 70 patients received SMILE in one eye and LASIK in the other eye for myopia and myopic astigmatism. FOZ was calculated using custom software on 3-month postoperative refractive power maps (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). Programmed treatment area was defined as the total area of the programmed OZ plus the transition zone. Centration was evaluated by the linear distance between FOZ centroid and the pupil center and the corneal apex.

RESULTS

The average preoperative spherical equivalent (-5.38 ± 1.65 vs -5.45 ± 1.61 diopters [D]), postoperative spherical equivalent (0.05 ± 0.39 vs 0.06 ± 0.39 D), uncorrected distance visual acuity (0.01 ± 0.13 vs 0.00 ± 0.08 logMAR), and corrected distance visual acuity (-0.07 ± 0.10 vs -0.07 ± 0.10 logMAR) were comparable in SMILE- and LASIK-treated eyes of the 60 patients with complete datasets (P > .419). Postoperative increase in spherical aberration was lower in SMILE than in LASIK (0.08 ± 0.16 vs 0.17 ± 0.18 µm, P = .002). The FOZ area was significantly larger in SMILE than in LASIK (30.25 ± 3.60 vs 29.21 ± 3.72 mm²), despite the smaller programmed OZ diameter (6.48 ± 0.08 vs 6.52 ± 0.11 mm) and smaller programmed treatment area (33.87 ± 0.81 vs 46.30 ± 2.61 mm², P < .037). Pupil centration (0.43 ± 0.21 vs 0.41 ± 0.22 mm) and apex centration (0.48 ± 0.24 vs 0.48 ± 0.22 mm) were comparable between SMILE and LASIK (P > .694).

CONCLUSIONS

SMILE created a larger FOZ than LASIK, despite the smaller programmed OZ. This may be due to a difference in the biomechanical response between the two procedures. Visual outcome and centration were comparable between SMILE and LASIK. [J Refract Surg. 2019;35(4):230-237.].

Decentration measurements using Placido corneal tangential curvature topography and Scheimpflug tomography pachymetry difference maps after small-incision lenticule extraction

PURPOSE

To assess the agreement of decentration measurements between tangential curvature topography and tomography pachymetry difference maps after a small-incision lenticule extraction (SMILE) procedure.

SETTING

Yonsei University College of Medicine and Eyereum Eye Clinic, Seoul, South Korea.

DESIGN

Retrospective case series.

METHODS

Decentrations and pupillary offset (angle κ) were analyzed and compared using two different methods. A difference map of the tangential curvature was generated with a Placido corneal topographer (Keratron Scout) and a pachymetry difference map was generated with a Scheimpflug tomographer (Pentacam) for each eye, using preoperative and 3-month postoperative scans. Decentrations were also compared using a vector difference plot for the two maps.

RESULTS

The study comprised 155 eyes (155 patients). The magnitude of decentration was 0.27 mm ± 0.17 (SD) (range 0.02 to 0.88 mm) with the tangential curvature difference maps and 0.26 ± 0.20 mm (range 0.00 to 0.91 mm) with the pachymetry difference maps, showing no significant difference in the arithmetic values of decentration (P = .124). However, the vector difference in pupillary offset between preoperative and postoperative measurements from the pachymetry difference map significantly correlated with the magnitude of vector differences of decentration between the two maps (P = .007). The vector difference plot also showed a wide distribution spread to all 4 quadrants, demonstrating a lack of agreement.

CONCLUSIONS

Although there was no significant difference between the scalar magnitude of decentration with the tangential topography difference maps and tomography pachymetry difference maps, the vector differences did not agree and increasing error was present with increasing differences in pupillary offset in the pachymetry difference maps.

Clinical study on combining femtosecond thin- flap and LASIK with the Triple-A profile for high myopia correction

BACKGROUND

Femtosecond laser-assisted LASIK (FS-LASIK) can make ultra-thin corneal flap accurately. MEL 90 excimer laser provides Triple-A ablation mode, which significantly reduces the amount of corneal tissue cutting. This study aimed to investigate the visual and refractive outcomes in patients with high myopia after thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile.

METHODS

This prospective study included 90 eyes from 90 patients received thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile. According to the pre-operative spherical equivalence (SE), the treated eyes were divided into two groups: the first group (ranged from - 9.0D to - 6.0D) and the second group (ranged from - 11.15D to - 9.0 D). The parameters evaluated pre-operatively and 6 month post-operatively included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, efficacy and safety index, posterior central elevation, and corneal higher-order aberrations (HOAs).

RESULTS

The efficacy indexes were 1.149 ± 0.150 for the first group and 1.173 ± 0.136 for the second group (P > 0.05), whereas safety indexes were 1.135 ± 0.154 and 1.158 ± 0.137 (P > 0.05) respectively. Moreover, 93.8 and 90.6% of patients had an UDVA of 20/20, 51.2 and 49.8% had a UDVA of 20/16 for the first and second groups, respectively; yet, there were no significant differences between both groups at the 20/20 and the 20/16 levels (P > 0.05). 84 and 100% of the firse group patients had a SE within ±0.5 D and ± 1.0 D, and 82 and 100% of the second group patients. There was no significant myopia regression in both groups after 6 months follow-up. At 1, 3 and 6-month after surgery, there were no significant differences in the posterior central elevation between the two groups (P > 0.05). The induction of total HOAs, spherical aberration, and horizontal coma in the first group were significantly less than that in the second group at the 6- month follow-up (P < 0.05), while the differences of the RMS value of vertical coma between both groups were not significant (P > 0.05). The ablation was significantly associated with the post-operative increase in total HOAs, spherical aberration and horizontal coma (P < 0.05),but not with vertical coma (P > 0.05).

CONCLUSION

Our results indicate that using the Triple-A ablation profile of the MEL 90 excimer laser associated with thin-flap is a safe, efficient, and predictable method to correct SE up to - 11.15D. However, for patients with high myopia, under the premise of ensuring a certain optical zone diameter, the ablation depth should be minimized to reduce the increase of the post-operative HOAs so as to improve the visual quality.

Management of progressive keratoconus with partial topography-guided PRK combined with refractive, customized CXL - a novel technique: the enhanced Athens protocol

Purpose

To report a novel application of partial topography-guided photorefractive keratectomy combined with topographically customized, higher fluence, and variable pattern corneal cross-linking applied on the same day of the treatment of keratoconus.

Methods

A topography-guided partial photorefractive keratectomy treatment of maximum 30 µm over the thinnest cone area was applied initially followed by a 7 mm, 50 µm phototherapeutic keratectomy treatment to address epithelial removal. 0.02% Mitomycin C was applied for 20 seconds and then the exposed stroma was soaked with 0.1% riboflavin solution for 5 minutes. The cornea was then treated with a customized, variable-pattern and 20 mW/cm² fluence for a total of 5-10 J, and up to 15 J of energy was delivered with the KXL-II device employing an active tracker. The center of the pattern that received the 15 J was topography-matched with the thinnest area of the cone. Visual acuity, refractive error, cornea clarity, keratometry, topography, pachymetry with a multitude of modalities and endothelial cell density were evaluated over 36 months.

Results

Keratoconus was stabilized in all cases. The severity of keratoconus stage by Amsler- Krumeich criteria improved from an average of 3.2 (1-4) to 1.8 (0-3). Uncorrected distance visual acuity changed from preoperative 20/80 to 20/25 at 6 months. A maximum astigmatic reduction of 7.8 D (5.3-15.6), and a significant cornea surface normalization (an index of height decentration improvement from 0.155 [±0.065] to 0.045 [±0.042]) were achieved by 1 month and remained relatively stable for 36 months postoperatively. Two cases delayed full reepithelialization for up to 9 days.

Conclusion

This paper introduces a novel technique in order to maximize the refractive normalization effect along with ectasia stabilization in young keratoconus patients. This may facilitate the use of less tissue ablation, in comparison to utilizing a homogeneous UV light beam for corneal cross-linking in Athens Protocol cases. It broadens the number of potential candidate cases that would have been limited to employ this technique due to tissue thickness limitations.

Relationship Between Decentration and Induced Corneal Higher-Order Aberrations Following Small-Incision Lenticule Extraction Procedure

Purpose

To investigate the amount of lenticule decentration following small-incision lenticule extraction (SMILE) by using the Keratron Scout tangential topography difference map, and the relationship between the magnitudes of total decentration and induced corneal higher-order aberrations (HOAs).

Methods

This retrospective observational case series study analyzed decentration values obtained from the Keratron Scout tangential topography difference map of 360 eyes (360 patients) that underwent SMILE. Root mean square total HOAs, third order coma aberration, fourth order spherical aberration, as well as individual coefficients for vertical and horizontal coma were measured preoperatively and 3-months postoperatively. Simple linear regression analysis and piecewise regression models were used to determine the relationship between the magnitudes of total decentration and induced corneal HOAs.

Results

The mean total decentration distance from the corneal vertex was 0.36 ± 0.22 mm (range, 0.02-1.27 mm). There were significant differences in total HOAs, coma, vertical and horizontal comas, and spherical aberration between preoperative and 3-month postoperative assessments. Significant relationships between the magnitudes of total decentration and induced corneal HOAs were noted. Subgroup analysis according to the degree of total decentration (group I, total decentered displacement ≤0.335 mm; and group II, total decentered displacement >0.335 mm) revealed that induced changes in total HOAs, coma, vertical coma, and spherical aberration were significantly larger in group II than in group I.

Conclusions

A minimal degree of decentration was closely related to a smaller induction of corneal HOAs. Efforts to optimize centration are critical for achieving better surgical outcomes in SMILE.

Impact of a Displaced Corneal Apex in Small Incision Lenticule Extraction

PURPOSE

To evaluate the possible impact of a displaced corneal apex (point of maximum curvature) on visual results and tomographic parameters after small incision lenticule extraction (SMILE).

METHODS

In this retrospective evaluation, eyes with uncomplicated SMILE for myopia correction were classified in two groups based on their preoperative distance between the corneal apex and corneal vertex (corneal intercept with the patient's line of sight) of 1 mm or greater (large A-V distance) or less than 1 mm (small A-V distance). All surgeries were performed during the early learning curve of two surgeons. Visual outcome parameters included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refractive spherical equivalent (MRSE), and refractive astigmatism 3 months postoperatively. Scheimpflug-derived tomographic outcome parameters included mean keratometry value, root mean square higher order aberrations (RMS HOAs), and optical zone decentration.

RESULTS

The study comprised 94 eyes of 48 patients: 44 eyes in the large A-V distance group and 50 eyes in the small A-V distance group. Preoperative and postoperative RMS HOAs were significantly higher in the large A-V distance group than in the small A-V distance group (P = .002 and .008, respectively). Postoperative CDVA was significantly better in the small A-V distance group (P = .014). There were no statistically significant differences in postoperative UDVA, MRSE, refractive astigmatism, mean keratometry value, and optical zone decentration.

CONCLUSIONS

After SMILE, CDVA was significantly worse in eyes with a preoperatively displaced corneal apex compared to eyes with a more central corneal apex. However, good visual results were achieved in both groups. [J Refract Surg. 2018;34(7):460-465.].

Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK

PURPOSE

To evaluate the safety, efficacy, and contralateral eye comparison of topography-guided myopic LASIK with two different refraction treatment strategies.

SETTING

Private clinical ophthalmology practice.

PATIENTS AND METHODS

A total of 100 eyes (50 patients) in consecutive cases of myopic topography-guided LASIK procedures with the same refractive platform (FS200 femtosecond and EX500 excimer lasers) were randomized for treatment as follows: one eye with the standard clinical refraction (group A) and the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction; group B). All cases were evaluated pre- and post-operatively for the following parameters: refractive error, best corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), topography (Placido-disk based) and tomography (Scheimpflug-image based), wavefront analysis, pupillometry, and contrast sensitivity. Follow-up visits were conducted for at least 12 months.

RESULTS

Mean refractive error was -5.5 D of myopia and -1.75 D of astigmatism. In group A versus group B, respectively, the average UDVA improved from 20/200 to 20/20 versus 20/16; post-operative CDVA was 20/20 and 20/13.5; 1 line of vision gained was 27.8% and 55.6%; and 2 lines of vision gained was 5.6% and 11.1%. In group A, 27.8% of eyes had over -0.50 diopters of residual refractive astigmatism, in comparison to 11.7% in group B (P<0.01). The residual percentages in both groups were measured with refractive astigmatism of more than -0.5 diopters.

CONCLUSION

Topography-modified refraction (TMR): topographic adjustment of the amount and axis of astigmatism treated, when different from the clinical refraction, may offer superior outcomes in topography-guided myopic LASIK. These findings may change the current clinical paradigm of the optimal subjective refraction utilized in laser vision correction.

Advances in Refractive Surgery: June 2014 to July 2015

PURPOSE

The objective of this study was to review the advances in the field of refractive surgery as reported in the peer-reviewed literature during the previous year.

DESIGN

A literature review.

METHODS

In this review, we highlight the most pertinent articles in the field from June 2014 to the end of July 2015.

RESULTS

This past year has seen a growing body of research on small-incision lenticule extraction, presbyopic inlays, and phakic intraocular lenses, as more clinicians are adopting these techniques into their armamentarium.

CONCLUSIONS

Laser-assisted in situ keratomileusis and photorefractive keratectomy continue to dominate the keratorefractive literature, as they remain the most frequently performed refractive surgeries.