Comparison of two novel swept-source optical coherence tomography devices to a partial coherence interferometry-based biometer.

To evaluate the repeatability and agreement of corneal and biometry measurements obtained with two swept-source optical coherence tomography (SSOCT) and a partial coherence interferometry-based device. This is a cross-sectional study. Forty-eight eyes of 48 patients had three consecutive measurements for ANTERION (Heidelberg Engineering, Germany), CASIAII (Tomey, Japan) and IOLMaster500 (Carl Zeiss Meditec, USA) on the same visit. Mean keratometry (Km), central corneal thickness (CCT), anterior chamber depth (ACD) and axial length (AL) were recorded. Corneal astigmatic measurements were converted into vector components-J0 and J45. Intra-device repeatability and agreements of measurements amongst the devices were evaluated using repeatability coefficients (RCs) and Bland-Altman plots, respectively. All devices demonstrated comparable repeatability for Km (p ≥ 0.138). ANTERION had the lowest RC for J0 amongst the devices (p ≤ 0.039). Systematic difference was found for the Km and J0 obtained with IOLMaster500 compared to either SSOCTs (p ≤ 0.010). The ACD and AL measured by IOLMaster500 showed a higher RC compared with either SSOCTs (p < 0.002). Systematic difference was found in CCT and ACD between the two SSOCTs (p < 0.001), and in AL between ANTERION and IOLMaster500 (p < 0.001), with a mean difference of 1.6 µm, 0.022 mm and 0.021 mm, respectively. Both SSOCTs demonstrated smaller test-retest variability for measuring ACD and AL compared with IOLMaster500. There were significant disagreement in keratometry and AL measurements between the SSOCTs and PCI-based device; their measurements should not be considered as interchangeable.

Accuracy and Precision of Intraocular Lens Calculations Using the New Hill-RBF Version 2.0 in Eyes With High Axial Myopia.

PURPOSE: To compare the accuracy and precision of the new Hill-RBF version 2.0 (Hill-RBF 2) formula with other formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, and SRK/T) in predicting residual refractive error after phacoemulsification in high axial myopic eyes. DESIGN: Retrospective case series. METHODS: 127 eyes of 127 patients with axial length (AL) ≥26 mm were included. The refractive prediction error (PE) was calculated as the difference between the postoperative refraction and the refraction predicted by each formula for the intraocular lens (IOL) power actually implanted. Standard deviation (SD) of PE, median absolute PE (MedAE), proportion of eyes within ±0.25, ±0.50, and ±1.00 diopter (D) of PE were compared. A generalized linear model was used to model the mean function and variance function of the PE (indicative of the accuracy and precision) with respect to biometric variables. RESULTS: The MedAE and SD of Hill-RBF 2 were lower than that of Hoffer Q, Holladay 1, and SRK/T (P ≤ .036) and were comparable to Barrett Universal II and Haigis (P ≥ .077). Hill-RBF 2 had more eyes within ±0.25 D of the intended refraction (76 out of 127 eyes [59.84%]) compared to other formulas (P ≤ .034) except Barrett Universal II (P = .472). AL was associated with the mean function or variance function of the PE for all formulas except Hill-RBF 2. CONCLUSIONS: In this study, the precision of Hill-RBF 2 is comparable to Barret Universal II and Haigis. Unlike the other 5 formulas, its dispersion and the accuracy of the refractive prediction is independent of the AL.

Vector analysis of high (≥3 diopters) astigmatism correction using small-incision lenticule extraction and laser in situ keratomileusis.

PURPOSE: To compare the astigmatic correction in high myopic astigmatism between small-incision lenticule extraction and laser in situ keratomileusis (LASIK) using vector analysis. SETTING: Hong Kong Laser Eye Center, Hong Kong. DESIGN: Retrospective case series. METHODS: Patients who had correction of myopic astigmatism of 3.0 diopters (D) or more and had either small-incision lenticule extraction or femtosecond laser-assisted LASIK were included. Only the left eye was included for analysis. Visual and refractive results were presented and compared between groups. RESULTS: The study comprised 105 patients (40 eyes in the small-incision lenticule extraction group and 65 eyes in the femtosecond laser-assisted LASIK group.) The mean preoperative manifest cylinder was -3.42 D ± 0.55 (SD) in the small-incision lenticule extraction group and -3.47 ± 0.49 D in the LASIK group (P = .655). At 3 months, there was no significant between-group difference in uncorrected distance visual acuity (P = .915) and manifest spherical equivalent (P = .145). Ninety percent and 95.4% of eyes were within ± 0.5 D of the attempted cylindrical correction for the small-incision lenticule extraction and LASIK group, respectively (P = .423). Vector analysis showed comparable target-induced astigmatism (P = .709), surgically induced astigmatism vector (P = .449), difference vector (P = .335), and magnitude of error (P = .413) between groups. The absolute angle of error was 1.88 ± 2.25 degrees in the small-incision lenticule extraction group and 1.37 ± 1.58 degrees in the LASIK group (P = .217). CONCLUSION: Small-incision lenticule extraction offered astigmatic correction comparable to LASIK in eyes with high myopic astigmatism.

Comparative evaluation of progression rate in keratoconus before and after collagen crosslinking.

PURPOSE: To compare the rate of disease progression in keratoconus before and after corneal collagen crosslinking (CXL). METHODS: 145 eyes were followed without CXL (no-CXL group) for a median duration of 31 months whereas 45 eyes were followed up for 41 months before (pre-CXL) and after (post-CXL) accelerated, epithelium-off crosslinking. Progression was defined based on significant slope found in linear mixed effect models against time. Swept-source optical coherence tomography was used for measurement of anterior steep keratometry, anterior flat keratometry (Ant Kf), anterior average keratometry (Ant Avg K); posterior steep keratometry, posteriorflat keratometry (Post Kf), posterior average keratometry (Post Avg K) and corneal thickness. RESULTS: The patients in pre-CXL group were significantly younger (26.3±5.48 years) compared with the patients in no-CXL group (32.7±10.24 years) (P=0.004). Significant differences were observed during baseline examination for all parameters (P≤0.035) between pre-CXL and no-CXL groups except Ant Cyl and Post Cyl. During observation period, statistically significant differences were noted between pre-CXL and no-CXL groups in the progression rate of Ant Kf, Ant Avg K, Post Kf and Post Avg K (P≤0.045). After CXL, the progression rate in post-CXL group was comparable to that in no-CXL group. All corneal parameters remained stable in no-CXL group throughout the follow-up period. CONCLUSIONS: Serial tomographic examination is useful to document disease progression before and after CXL. In our study, a decrease in progression rate of corneal parameters was noted after CXL. In cases with stable corneal parameters over time, careful monitoring can be considered instead of collagen crosslinking.

Conventional Versus Inverted Side-cut Flaps for Femtosecond Laser-Assisted LASIK: Laboratory and Clinical Evaluation.

PURPOSE: To study the differences in early corneal cellular events and biomechanical properties after femtosecond laser-assisted LASIK performed using conventional or inverted side-cut angles. METHODS: In the laboratory study, left eyes of 24 rabbits underwent LASIK flap creation with a 70° or 115° side-cut. The contralateral eyes served as controls. The corneas were harvested 24 hours postoperatively. In the clinical study, 2 eyes of each patient (n = 29) were randomized to corneal flap creation with 70° or 115° side-cut angles during LASIK. The Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Depew, NY) was used to assess biomechanical properties of the cornea. RESULTS: In rabbit eyes, epithelial ingrowth was observed more frequently in flaps with 70° side cuts compared to flaps with 115° side-cuts. Corneas with 70° side-cuts showed significantly increased apoptotic cells compared to 115° side-cuts in the central (P = .001) and peripheral (P = .004) regions. Fifty-eight eyes of 29 patients were included in the clinical study. An overall reduction in Goldmann-correlated intraocular pressure, corneal-compensated intraocular pressure, corneal resistance factor, corneal hysteresis measurements, p1 area, p2 area, and p1 area 1 and p2 area 1 was noted 37 ± 2 months after surgery (P < .001). No significant difference was observed in the change of any of these parameters between both groups (P ≥ .146). CONCLUSIONS: Significant differences in wound healing were observed in rabbit corneas that underwent LASIK with conventional or inverted side-cuts. Variation in flap side-cut angles did not alter the long-term biomechanical properties measured with the ORA in patients after LASIK. [J Refract Surg. 2017;33(2):96-103.].

Longitudinal comparison of femtosecond-assisted sub-Bowman keratomileusis versus photorefractive keratectomy for high myopia.

PURPOSE: To longitudinally compare the visual and refractive outcomes and changes in corneal thickness between femtosecond-assisted sub-Bowmen keratomileusis (SBK) and photorefractive keratectomy (PRK) with mitomycin C in eyes with high myopia. METHODS: Patients with spherical equivalent ≥6 dioptres (D) who underwent femtosecond-assisted SBK or PRK with mitomycin C were recruited. All patients were examined preoperatively and after 1 week, and, 1, 3, 6 and 12 months postoperatively. Assessments included uncorrected and best-corrected distance visual acuity , and manifest refraction spherical equivalent. Corneal thickness was measured using swept source optical coherence tomography. RESULTS: A total of 110 eyes were included (68 PRK, 42 SBK). Change in efficacy index and safety index was not significantly different between both groups beyond 1 week postoperatively (p≥0.116). Manifest refraction spherical equivalent changed significantly from -9.02±1.92 D preoperatively to -0.21±0.31 D and from -8.25±1.10 D preoperatively to -0.53±0.55 D at 1 year after PRK and SBK, respectively (p<0.0001). The variance of postoperative refraction was significantly smaller after PRK throughout the 1-year follow-up compared with SBK (p≤0.0024). The central corneal thickness stabilised at 1 week after PRK and 3 months after SBK. CONCLUSIONS: Our study showed that femtosecond-assisted SBK and PRK with mitomycin C have comparable safety and efficacy for correction of high myopia. However, better predictability of postoperative refraction was noted after PRK compared with SBK.

Short-term Variance of Refractive Outcomes After Simultaneous LASIK and High-Fluence Cross-linking in High Myopic Correction.

PURPOSE: To analyze the visual and refractive outcomes of LASIK with and without simultaneous cross-linking for correction of myopia. METHODS: Patients who received femtosecond laser-assisted LASIK with and without adjunctive cross-linking according to patient's preference were examined longitudinally for 6 months. Patients with myopic manifest refraction spherical equivalent of 5.00 diopters (D) or greater and estimated residual stromal thickness of greater than 250 µm were included. RESULTS: Overall, 120 eyes of 60 patients were included (60 eyes of 30 patients for LASIK with cross-linking; 60 eyes of 30 patients with LASIK only). No significant difference was observed in age, preoperative corrected distance visual acuity, manifest refraction spherical equivalent, manifest sphere and cylinder, minimal corneal thickness, and residual stromal bed thickness between both groups (P ≥ .245). The uncorrected distance visual acuity and efficacy index were significantly worse on day 1 in eyes receiving adjunctive cross-linking (P = .0001). At 6 months, 86.7% and 95% of the eyes achieved uncorrected distance visual acuity of 20/25 or better in LASIK with cross-linking and LASIK only, respectively. The variance of postoperative spherical equivalent and sphere was significantly higher in eyes undergoing LASIK with cross-linking from 1 week up to 6 months compared to LASIK only (P ≤ .002). None of the patients required re-treatment up to 6 months postoperatively. CONCLUSIONS: Adjunctive cross-linking during LASIK was associated with worse visual outcomes during the first postoperative week. The variance of spherical equivalent was also high in these patients over a 6-month follow-up. [J Refract Surg. 2016;32(10):664-670.].

Early outcomes after small incision lenticule extraction and photorefractive keratectomy for correction of high myopia.

We prospectively compared visual and refractive outcomes in patients with high myopia and myopic astigmatism after small-incision lenticule extraction (SMILE) and photorefractive keratetctomy (PRK) with mitomycin C. Sixty-six eyes of 33 patients (mean age, 29.7 ± 5.6 years) were included (SMILE: 34 eyes, PRK 32 eyes). Preoperatively, no significant difference was noted in manifest spherical equivalent (p = 0.326), manifest sphere (p = 0.277), and manifest cylinder (p = 0.625) between both groups. At 1 month, there were significant differences in logMAR uncorrected distance visual acuity, efficacy index and manifest refraction spherical equivalent between SMILE and PRK (p ≤ 0.029). At 6 months, the logMAR corrected distance visual acuity (p = 0.594), logMAR uncorrected visual acuity (p = 0.452), efficacy index (p = 0.215) and safety index was (p = 0.537) was comparable between SMILE and PRK. Significant differences were observed in postoperative manifest spherical equivalent (p = 0.044) and manifest cylinder (p = 0.014) between both groups. At the end of 6 months, 100% of the eyes in SMILE group and 69% of the eyes in PRK group were within ±0.50 D of the attempted cylindrical correction. The postoperative difference vector, magnitude of error and absolute angle of error were significantly smaller after SMILE compared to PRK (p ≤ 0.040) implying a trend towards overcorrection of cylindrical correction following PRK.

Epithelium-on corneal collagen crosslinking for management of advanced keratoconus.

PURPOSE: To report the 1-year visual and keratometric results of epithelium-on corneal collagen crosslinking (CXL) for advanced keratoconus (median maximum keratometry [K] ≥58.0 diopters [D]). SETTING: School of Ophthalmology and Optometry and Eye Hospital of Wenzhou Medical College, Wenzhou, China. DESIGN: Prospective case series. METHODS: Patients with bilateral progressive keratoconus had tetracaine-enhanced epithelium-on CXL. The worse eye had CXL, and the fellow eye was not treated. Results were reported 1, 3, 6, and 12 months postoperatively. The outcomes were compared with those in the fellow untreated eyes. RESULTS: Twenty-one eyes of 21 patients with a median age of 20.4 years (interquartile range [IQR], 9.5 years) were treated. A significant improvement in postoperative uncorrected distance visual acuity was observed at 12 months (P = .002). Postoperative corrected distance visual acuity improved at 6 months and 12 months (P ≤ .009) compared with baseline values. The maximum K decreased by 1.63 D from the median preoperative maximum K of 62.7 D (IQR, 12.9 D) at 12 months (P < .001). The reduction in maximum K was higher after CXL than in untreated eyes at the end of 12 months (P = .001). Correlation analysis between the preoperative maximum K values and the change over 6 to 12 months between different studies showed a significant correlation (r = -0.764, P < .001; Spearman correlation). CONCLUSIONS: Epithelium-on CXL was an effective treatment for patients with advanced keratoconus. A higher preoperative maximum K value correlated with greater corneal flattening after CXL. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Randomized, contralateral eye study to evaluate the effect of standard and inverted side-cut angle on corneal biomechanical properties during femtosecond laser-assisted in situ keratomileusis.

PURPOSE: To evaluate the effect of side-cut angle profile on corneal biomechanical properties after femtosecond laser in situ keratomileusis (FS-LASIK). METHODS: Ninety-six myopic eyes of 48 patients underwent FS-LASIK. One eye of each patient was randomized to flap creation with a side-cut angle of 115°. The fellow eye flap side-cut angle was adjusted to 70°. Mean absolute error of flap diameter and mean change in Goldmann-correlated intra-ocular pressure (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), corneal resistance factor (CRF), p1 area, p2 area, p1 area 1 and p2 area 1 were compared between both groups. RESULTS: Overall, the mean IOPg and CRF showed significant reduction at the end of 1 and 3 months, as well as between 1 and 3 months postoperatively (p ≤ 0.03). The mean IOPcc and CH showed significant reduction (p < 0.001) at the end of 3 months postoperatively. The parameters p1 area, p2 area, p1 area 1 and p2 area 1 changed significantly at the end of 1 and 3 months postoperatively (p < 0.001). There was no significant difference between both groups with regards to the mean change of IOPg, IOPcc, CH, CRF, p1 area, and p1 area 1. In 115° group, the mean absolute error in flap diameter was greater compared with 70° group (p = 0.014). CONCLUSIONS: The stability of IOP and corneal biomechanical properties were not enhanced in FS-LASIK flaps with an inverted side-cut angle. The size of corneal flap created with 70° side-cut angle was more accurate compared with 115° side-cut angle.