Corneal biomechanical properties after LASIK, ReLEx flex, and ReLEx smile by Scheimpflug-based dynamic tonometry.

PURPOSE: To evaluate corneal biomechanical properties after LASIK, ReLEx flex, and the flap-free procedure ReLEx smile by Scheimpflug-based dynamic tonometry (Corvis ST) and non-contact differential tonometry (Ocular Response Analyzer, ORA). METHODS: Patients treated for high myopia (-10.5 to -5.5 diopters, spherical equivalent refraction) more than one year previously at Aarhus University Hospital were included. Treatments comprised LASIK (35 eyes), ReLEx flex (31 eyes), and ReLEx smile (29 eyes). A control group included 31 healthy eyes. Cornea-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured with ORA. Corneal applanation and deformation were registered with Corvis ST during an air-pulse. RESULTS: Multiple linear regression analysis showed that CH and CRF were significantly lower after all keratorefractive procedures compared to healthy controls (p < 0.05). No significant differences were observed in CH or CRF between the keratorefractive groups. Corvis ST showed no differences in radius at highest concavity (HC radius), time until first applanation (A1 Time), time until second applanation (A2 Time), and deflection length at highest concavity (HC deflection length) between groups. LASIK treated eyes had significantly shorter time until highest concavity than eyes treated with ReLEx smile (HC Time, p = 0.01). The A1 deflection length was significantly shorter in the keratorefractive groups compared to the healthy controls (p < 0.05). CONCLUSIONS: Keratorefrative procedures alter the corneal biomechanical properties with regard to corneal hysteresis and corneal resistant factor. The flap-based LASIK and ReLEx flex and the flap-free ReLEx smile result in similar reduction in corneal biomechanics when evaluated by Corvis ST and ORA.

Changes in Astigmatism, Densitometry, and Aberrations After SMILE for Low to High Myopic Astigmatism: A 12-Month Prospective Study.

PURPOSE: To evaluate 12-month changes in refraction, visual outcome, corneal densitometry, and postoperative aberrations after small incision lenticule extraction (SMILE) for myopic astigmatism. METHODS: This 12-month prospective clinical trial comprised 101 eyes (101 patients) treated with SMILE for myopic astigmatism with cylinder of 0.75 to 4.00 diopters (D). The preoperative, 1-week, and 1-, 3-, 6-, 9-, and 12-month examinations included measurement of manifest refraction, uncorrected distance visual acuity (UDVA), and corrected (CDVA) distance visual acuity. Astigmatic error vector analysis was performed using Al-pin's method. Densitometry and aberrations were evaluated with Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany). RESULTS: Preoperative spherical equivalent averaged -6.78 ± 1.90 D with 1.81 ± 1.00 D in cylinder correction. After 12 months, 74% and 93% of the eyes were within ±0.50 and ±1.00 D of the attempted refraction, respectively. The logMAR UDVA and CDVA averaged 0.03 ± 0.16 and -0.08 ± 0.09, respectively. Vector analysis showed a with-the-rule undercorrection at 12 months with a mean difference vector of 0.31 D @ 91°. There was a minor counterclockwise rotation of the axis, with an arithmetic angle of error of 0.34° ± 14°. An undercorrection of approximately 11% per diopter of attempted correction was seen at 12 months. Spherical aberrations, coma, and higher order aberrations remained stable during the postoperative period (P < .09). After 12 months, no increase in densitometry could be identified. CONCLUSIONS: Treatment of astigmatism with SMILE seems to be predictable and effective, but with an astigmatic undercorrection of approximately 11% and a small counterclockwise rotation of the axis. [J Refract Surg. 2017;33(1):11-17.].

Contralateral Eye Comparison of SMILE and Flap-Based Corneal Refractive Surgery: Computational Analysis of Biomechanical Impact.

PURPOSE: Computational analyses were performed to quantify and directly compare the biomechanical impact of flapless and flap-based procedures in a series of patients undergoing small incision lenticule extraction (SMILE) in one eye and flap-based femtosecond lenticule extraction in the other. METHODS: Tomographic data from 10 eyes of 5 patients undergoing femtosecond laser refractive lenticule extraction for myopic astigmatism with or without a stromal flap (femtosecond lenticule extraction in one eye, SMILE in the contralateral eye) were used to generate computational models. Inverse finite element analyses were performed at physiologic intraocular pressure followed by forward analyses at elevated intraocular pressure to assess corneal displacement and stress under differential loading. Case-specific treatment settings were incorporated. Preoperative material constants were obtained through inverse finite element analyses, and the surgically induced change in fiber stiffness within each flap was determined by minimization of the error between the simulated and actual 6-month topographic outcomes. RESULTS: Flap-based procedures produced a 49% (range: 2% to 87%) greater mean reduction in effective stromal collagen fiber stiffness within the flap region than contralateral SMILE cases. Lower stresses and deformations were observed within the residual stromal bed in SMILE cases than in flap-based cases. Stromal bed displacements and stresses were more affected by a loading increase in flap-based eyes than flapless eyes. CONCLUSIONS: Intrastromal flapless procedures had less impact on anterior stromal collagen mechanics and resulted in lower stromal bed displacements and stresses than flap-based procedures in contralateral eyes. However, biomechanical impact varied widely between individuals and this reinforces the need for individualized assessment of ectasia risk. [J Refract Surg. 2017;33(7):444-453].

Three-Year Results of Small Incision Lenticule Extraction for High Myopia: Refractive Outcomes and Aberrations.

PURPOSE: To assess the 3-year refractive and visual outcomes after small incision lenticule extraction (SMILE) in patients with high myopia and to evaluate the optical changes from 3 months to 3 years after surgery. METHODS: A total of 87 eyes (87 patients) undergoing SMILE for high myopia were included. Preoperative and 3-month and 3-year postoperative follow-up examinations included manifest refraction and uncorrected and corrected distance visual acuities. Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany) was used to evaluate the total corneal refractive power and the root mean square of spherical aberration, coma, and total higher-order aberrations. The paired t test and Wilcoxon signed rank test were used. RESULTS: The preoperative spherical equivalent averaged -7.30 ± 1.40 diopters (D); no significant changes occurred between 3 months and 3 years after surgery (-0.30 ± 0.50 vs -0.40 ± 0.60 D, P = .071). Uncorrected distance visual acuity was stable from 3 months to 3 years after SMILE (0.04 ± 0.17 vs 0.03 ± 0.19 logMAR; P = .28), whereas corrected distance visual acuity improved from -0.05 ± 0.15 to -0.08 ± 0.11 logMAR (P < .001). At 3 months, 82% and 93% of eyes were within ± 0.50 and ± 1.00 D, respectively. At 3 years, 78% and 90% were within ± 1.00 D of the attempted refraction, respectively. Spherical and higher-order aberrations significantly decreased from 3 months to 3 years, whereas coma remained stable. A significant regression of 0.36 ± 0.29 D was seen in total corneal refractive power (P < .001). CONCLUSIONS: The refractive and visual outcomes seemed stable years after SMILE. A minor myopic regression was observed in total corneal refractive power but not in subjective refraction. There seems to be a significant long-term improvement in higher-order aberrations after surgery.

Repeatability, reproducibility, and age dependency of dynamic Scheimpflug-based pneumotonometer and its correlation with a dynamic bidirectional pneumotonometry device.

PURPOSE: To assess the repeatability, reproducibility, and age dependency of dynamic Scheimpflug-based pneumotonometry (Corvis)-generated parameters and their correlation with dynamic bidirectional pneumotonometry device [Ocular Response Analyzer (ORA)] measurements [corneal hysteresis (CH) and corneal resistance factor (CRF)]. METHODS: Eyes of 29 healthy participants between 20 and 30 years old were measured using Corvis and ORA. Measurements were performed twice in a row and repeated after 1 week. Repeatability and reproducibility were examined by calculating intraday and interday coefficients of variation (CVs). Corvis measurements were compared with measurements from 19 participants older than 65 years. RESULTS: The most repeatable and reproducible Corvis-generated parameters, with intraday and interday CVs < 10% were as follows: intraocular pressure (IOP), pachymetry, time to first and second applanation (A1 time, A2 time), radius and amplitude at highest concavity (HC radius and HC deformation amplitude, respectively), time to highest concavity (HC time), deflection length and amplitude at highest concavity [HC deflection length and HC deflection amplitude (millimeter), respectively], and time to highest deflection amplitude [HC deflection amplitude (millisecond)]. However, 7 of 19 analyzed parameters showed CVs > 10%. HC-related parameters showed significant age dependency. The correlation between Corvis and ORA was weak (A2 time and CH, r = 0.36, A1 time and CRF, r = 0.41). Corvis-derived IOP was on average 2.2 ± 2.3 mm Hg higher than cornea-compensated IOP, with large differences in patients with high-average IOP. CONCLUSIONS: The considerable variation in repeatability and reproducibility should be taken into account when using the Corvis. Corvis parameters showed poor correlation with CH and CRF obtained by ORA measurements.