Background:Accurate corneal evaluation is crucial for determining candidacy for refractive surgery.Devices combining diverse technologies, such as Scheimpflug imaging (Pentacam, Sirius), swept-source OCT (Anterion), and hybrid OCT/Placido systems (MS-39), offer distinct advantages and limitations in screening. Purpose:This study was conducted to compare corneal assessment with two Scheimpflug camera devices (Oculus Pentacam and CSO Sirius) and two spectral domain anterior segment optical coherence tomography devices (Heidelberg Engineering Anterion and CSO MS-39) in the preoperative screening of the cornea before refractive surgery. Methods:In this retrospective, consecutive case series, we enrolled 110 patients undergoing refractive surgery. Simulated keratometry (Sim-K), posterior keratometry (PK), central corneal thickness (CCT), keratometric astigmatism magnitude (KAM), Corneal diameter, Anterior chamber depth (ACD), and total corneal power (TCP) were compared using different instruments. To compare the mean values of the measurements, a repeated measures ANOVA was used. Results:Simulated keratometry (Sim-K), central corneal thickness (CCT), keratometric astigmatism magnitude (KAM), and total corneal power (TCP) showed a good agreement (ICC > 95%, ANOVA p > 0.05). Although posterior keratometry (PK) showed no significant differences, its Cronbach's alpha and ICC were low, indicating limited agreement. Corneal diameter showed moderate to poor ICC (p<0.001). Anterior chamber depth (ACD) showed the highest values when assessed with the Anterion; however, the results did not show a statistical significance (p > 0.05). Conclusion:Both Scheimpflug camera devices and AS-OCT were suitable instruments for evaluating the cornea before refractive surgery. A strong correlation was seen for Sim-K, CCT, CD, and TCP; however, notable discrepancies were identified in posterior keratometry, astigmatism magnitude, and ACD. These findings underscore the importance of device-specific factors in assessing corneal and anterior segment measures during refractive surgery evaluations.

Purpose To evaluate the value of total keratometry (TK) to estimate corneal power in eyes that underwent SMILE for treatment of myopia or myopic astigmatism in subgroups of low and high astigmatism. Methods The difference between preoperative and postoperative measurements of corneal power (Delta TCRP, Delta TK) was compared with the surgically induced refractive change at the corneal plane (Delta SEco) by Pearson correlation. Vector analysis of TCRP- and TK-derived astigmatism was performed to evaluate the corneal astigmatism. Single-angle plots were generated with the AstigMATIC tool for standard astigmatism vector analysis. Results Paired t-test revealed statistically significant differences in preoperative (p = .02) and postoperative (p = .0455) measurements between TK and TCRP in the group of high-level astigmatism and the postoperative low astigmatism group (p < .01). No significant differences were found in preoperative data in the group of low-level astigmatism (p = .60). The correlation of Delta SEco and TK (low astigmatism, R-2 = 0.978; high astigmatism R-2 = 0.980) was stronger than the correlation of TCRP 4.0 mm and Delta SEco (low astigmatism, R-2 = 0.743; high astigmatism R-2 = 0.959) in both astigmatic groups. The vector analysis demonstrated nearly identical results concerning the correction index (CI) for TK and TCRP. Comparing the difference vector (DV) between both parameters, TK-derived results were closer to the optimum. Conclusions The findings endorse TK as a reliable measure of corneal power after SMILE in patients with low and high astigmatism.

Myopia is the most common refractive error. Surgical correction with laser is possible. LASIK and SMILE are the techniques currently most used. Aim of the study was to compare changes in corneal volume and thickness after the respective laser treatment. 104 eyes of 52 patients were matched based on refractive error into two equally sized groups, either treated with LASIK or SMILE. Measurements were obtained from the Scheimpflug camera (Pentacam) preoperatively and at 3 and 12 months postoperatively. 3 months postoperatively, the flapless SMILE procedure resulted in a significant overall greater loss of corneal volume (P < 0.01) and corneal thickness (P < 0.01) compared to LASIK. No significant difference was found when comparing the 3 to 12-months values in each group. Within the currently used ranges of refractive error correction, loss in central corneal thickness and corneal volume with SMILE is higher in comparison to LASIK. As greater loss in corneal volume and thickness might contribute to higher level of corneal instability maximum ranges of refractive error correction with SMILE should not supersede those set currently for LASIK until more long-term results on corneal ectasia are available for SMILE.

PURPOSE:To gauge the value of total keratometry (TK) to estimate corneal power change in eyes that underwent small-incision lenticule extraction (SMILE) for treatment of myopia or myopic astigmatism.SETTING:Department of Ophthalmology, Ludwig-Maximilians-University, and SMILE Eyes Clinic Munich Airport, Munich, Germany.DESIGN:Prospective cross-sectional trial.METHODS:A total of 40 eyes of 40 patients who had undergone myopic SMILE were enrolled in this prospective study. Total corneal refractive power (TCRP; Pentacam HR) and TK (IOLMaster 700, Carl Zeiss Meditec AG) values were compared with the clinical history method (CHM). The surgically induced changes in TCRP (ΔTCRP) and TK (ΔTK) were also compared with the changes in spherical equivalent on the corneal plane (ΔSEco).RESULTS:Of the 40 eyes analyzed, the correlation between TK and CHM (R2 = 0.91, P < .001) was stronger than that between TCRP and CHM (R2 = 0.87, P < .001). When compared with the CHM, TCRP underestimated corneal power by a mean relative error of 0.59 diopter (D) and TK by 0.17 D. Linear regression analysis of ΔTCRP/ΔTK and the difference between preoperative and postoperative manifest refraction spherical equivalent at the corneal plane (ΔSEco) showed stronger correlation in ΔTK (R2 = 0.88) than that in ΔTCRP (R2 = 0.82).CONCLUSIONS:The findings endorse TK as an accurate measure for corneal power after myopic SMILE.

ZusammenfassungDie SMILE (small incision lenticule extraction) zählt zu den Verfahren der refraktiven Lentikel-Extraktion und hat sich im letzten Jahrzehnt zu einem etablierten Bestandteil des modernen refraktivchirurgischen Spektrums entwickelt. Dieser Beitrag gibt einen Überblick über Patientenselektion, Operationsmethode, mögliche Komplikationen und klinische Ergebnisse dieser Methode.