Comparison of corneal measurements in keratoconus eyes with two swept-source-optical coherence tomography devices and a Scheimpflug device.

PURPOSE: To assess the feasibility and reliability of biometric measurements taken with the Eyestar 900 device in keratoconus eyes in comparison with those taken with the Pentacam HR and IOLMaster 700. METHODS: Seventy-five eyes of 75 patients with keratoconus were included. The central corneal thickness (CCT), thinnest point of corneal thickness (TCT), axial length (AL), flat (K1) and steep (K2) anterior and posterior (Kp1, Kp2) keratometry, maximal keratometry (KMax) and anterior chamber depth (ACD) were compared between the Eyestar 900, Pentacam HR and IOLMaster 700. Reliability parameters such as the coefficient of variation (CoV) and intraclass correlation coefficient (ICC) were calculated. Pearson's r was determined to assess the correlation between devices. RESULTS: A high repeatability (CoV < 1%) and intraclass correlation (ICC > 0.9) was found for all devices, led by AL, TCT, K1 and K2 (CoV 0.01-0.36%; ICC 0.994-1.00). The largest correlation between devices was found for AL (Eyestar vs. IOLMaster, r = 1.0), K1 (Eyestar vs. IOLMaster, r = 0.997) and ACD (Eyestar vs. IOLMaster, r = 0.995; Pentacam vs. IOLMaster, r = 0.987; Eyestar vs. Pentacam, r = 0.983), but there were significant differences in measured values between devices (p < 0.001), whereas the correlation was only slightly lower (r = 0.947 to 0.994) for KMax, CCT, TCT, K2, Kp1 and Kp2. CONCLUSION: Keratometric and axial length measurements with the Eyestar 900 were feasible and revealed a high repeatability and a good correlation to the other devices in eyes with keratoconus.

Unilateral intraindividual comparison and bilateral performance of a monofocal spherical and diffractive extended depth of field intraocular lens mix-and-match approach.

BACKGROUND: To evaluate the intraindividual visual performance of a spherical and extended depth of field (EDOF) IOL used in a mix-and-match approach. METHODS: Single centre (tertiary care centre), retrospective consecutive case series. Included patients had uneventful cataract surgery with implantation of a spherical monofocal IOL (CT Spheris 204) in the dominant eye and a diffractive EDOF IOL (AT LARA 829) in the non-dominant eye. Monocular and binocular defocus curves and visual acuity at various distances were assessed. In addition, binocular reading speed, contrast sensitivity, and patient satisfaction using QOV, Catquest 9SF, and glare/halo questionnaires are reported. RESULTS: A total of 29 patients (58 eyes) were included. We observed significant intra-individual differences for monocular DCIVA, DCNVA, UIVA, and UNVA. There were no differences in monocular BCDVA or UDVA. The monocular defocus curves for the two IOLs significantly differed at defocus steps between -1.0 and -3.5 D. 93.10% of patients reported they would opt for the same combination of IOLs. CONCLUSION: Excellent uncorrected and corrected distance visual acuity was demonstrated in both groups. The mix-and-match approach described in this study yielded good intermediate vision and improved near vision with high-patient satisfaction.

Corneal biomechanics and diagnostics: a review.

PURPOSE: Corneal biomechanics is an emerging field and the interest into physical and biological interrelations in the anterior part of the eye has significantly increased during the past years. There are many factors that determine corneal biomechanics such as hormonal fluctuations, hydration and environmental factors. Other factors that can affect the corneas are the age, the intraocular pressure and the central corneal thickness. The purpose of this review is to evaluate the factors affecting corneal biomechanics and the recent advancements in non-destructive, in vivo measurement techniques for early detection and improved management of corneal diseases. METHODS: Until recently, corneal biomechanics could not be directly assessed in humans and were instead inferred from geometrical cornea analysis and ex vivo biomechanical testing. The current research has made strides in studying and creating non-destructive and contactless techniques to measure the biomechanical properties of the cornea in vivo. RESULTS: Research has indicated that altered corneal biomechanics contribute to diseases such as keratoconus and glaucoma. The identification of pathological corneas through the new measurement techniques is imperative for preventing postoperative complications. CONCLUSIONS: Identification of pathological corneas is crucial for the prevention of postoperative complications. Therefore, a better understanding of corneal biomechanics will lead to earlier diagnosis of ectatic disorders, improve current refractive surgeries and allow for a better postoperative treatment.

Depth-dependent mechanical properties of the human cornea by uniaxial extension.

The purpose of this study was to investigate the depth-dependent biomechanical properties of the human corneal stroma under uniaxial tensile loading. Human stroma samples were obtained after the removal of Descemet's membrane in the course of Descemet's membrane endothelial keratoplasty (DMEK) transplantation. Uniaxial tensile tests were performed at three different depths: anterior, central, and posterior on 2 × 6 × 0.15 mm strips taken from the central DMEK graft. The measured force-displacement data were used to calculate stress-strain curves and to derive the tangent modulus. The study showed that mechanical strength decreased significantly with depth. The anterior cornea appeared to be the stiffest, with a stiffness approximately 18% higher than that of the central cornea and approximately 38% higher than that of the posterior layer. Larger variations in mechanical response were observed in the posterior group, probably due to the higher degree of alignment of the collagen fibers in the posterior sections of the cornea. This study contributes to a better understanding of the biomechanical tensile properties of the cornea, which has important implications for the development of new treatment strategies for corneal diseases. Accurate quantification of tensile strength as a function of depth is critical information that is lacking in human corneal biomechanics to develop numerical models and new treatment methods.

Brillouin Spectroscopy in Ophthalmology. / Gegenwärtiger Stand der Brillouin-Spektroskopie in der Ophthalmologie.

BACKGROUND: Information about corneal biomechanics is crucial for achieving satisfactory outcomes after surgical corneal interventions, e.g., for astigmatic keratotomies, but also to identify corneas that are at risk for postoperative complications such as corneal ectasia. Hitherto, approaches to characterize corneal biomechanics in an in vivo setting have yielded only minor success, demonstrating the unmet medical need for a diagnostic technique to measure ocular biomechanics. OBJECTIVE: This review shall explain the mechanism of Brillouin spectroscopy and summarize the current scientific knowledge for ocular tissue. METHODS: PubMed research of relevant experimental and clinical publications, as well as reporting of own experience using Brillouin spectroscopy. RESULTS: Brillouin spectroscopy can measure different biomechanical moduli with a high spatial resolution. Currently, available devices are able to detect focal corneal weakening, e.g., in keratoconus, as well as stiffening after corneal cross-linking. Also, the mechanical properties of the crystalline can be measured. Corneal anisotropy and hydration, together with the dependence on the angle of the incident laser beam in Brillouin spectroscopy, are challenges in the precise interpretation of measured data. A clear advantage in the detection of subclinical keratoconus compared to corneal tomography, however, has not been shown yet. CONCLUSION: Brillouin spectroscopy is a technique to characterize biomechanical properties of ocular tissue in vivo. Published results confirm ex vivo data of ocular biomechanics; however, further improvements in the acquisition and interpretation of measured data are required until this technique can be used in a clinically viable setting.

Evaluation of the Use of Intraoperative OCT in Routine Surgery: A Two-year Comparison. / Evaluation der Nutzung von intraoperativer OCT im operativen Alltag: ein 2-Jahres-Vergleich.

BACKGROUND: In recent years, an increasing number of surgical microscopes fitted with an OCT module (intraoperative OCT, iOCT) have become available, providing high-resolution images of the surgical site in real time. While a 2018 survey at our hospital showed that iOCT delivered an additional intraoperative benefit in only 2.4% of all operations, considering that the manufacturer had since revised the hardware and software, we conducted a second user evaluation of this technology. MATERIAL AND METHODS: Prospective monocentric analysis of the application and user-friendliness of an EnFocus Ultra-Deep OCT (Leica Microsystems) over a period of 25 (2018) and 20 working days (2021). A standardized questionnaire was used to assess the surgeons' use of iOCT and its influence on the surgical course. RESULTS: 118 operations were performed over a 25-day period in 2018 and 92 operations were performed over a 20-day period in 2021. In 2018, iOCT was used in 24.6% and in 2021 in 48.9% of all surgeries, with iOCT proving to be "critical" to the surgical course in 2.4% and 3.3% of cases, respectively, as assessed by the surgeons in both years. These were operations in which the intraocular view was limited, e.g., with decompensated cornea, vitreous hemorrhage, or after previous surgery, e.g., after penetrating keratoplasty. CONCLUSION: Further development of the user interface led to an improvement in usability, and the iOCT was used significantly more often. In both years, the iOCT proved to be critical for the course of the surgery in a comparably small number of operations, especially those involving complex situations.

Orientation and depth dependent mechanical properties of the porcine cornea: Experiments and parameter identification.

The porcine cornea is a standard animal model in ophthalmic research, making its biomechanical characterization and modeling important to develop novel treatments such as crosslinking and refractive surgeries. In this study, we present a numerical model of the porcine cornea based on experimental measurements that captures both the depth dependence and orientation dependence of the mechanical response. The mechanical parameters of the established anisotropic hyperelastic material models of Gasser, Holzapfel and Ogden (HGO) and Markert were determined using tensile tests. Corneas were cut with a femtosecond laser in the anterior (100 µm), central (350 µm), and posterior (600 µm) regions into nasal-temporal, superior-inferior, and diagonal strips of 150 µm thickness. These uniformly thick strips were tested at a low speed using a single-axis testing machine. The results showed that the corneal mechanical properties remained constant in the anterior half of the cornea regardless of orientation, but that the material softened in the posterior layer. These results are consistent with the circular orientation of collagen observed in porcine corneas using X-ray scattering. In addition, the parameters obtained for the HGO model were able to reproduce the published inflation tests, indicating that it is suitable for simulating the mechanical response of the entire cornea. Such a model constitutes the basis for in silico platforms to develop new ophthalmic treatments. In this way, researchers can match their experimental surrogate porcine model with a numerical counterpart and validate the prediction of their algorithms in a complete and accessible environment.

Biometry and Intraocular Lens Power Calculation in Eyes with Prior Laser Vision Correction (LVC) - A Review.

BACKGROUND: An intraocular lens (IOL) calculation in eyes that have undergone laser vision correction (LVC) poses a significant clinical issue in regards to both patient expectation and accuracy. This review aims to describe the pitfalls of IOL power calculation after LVC and give an overview of the current methods of IOL power calculation after LVC. REVIEW: Problems after LVC derive from the measurement of anterior corneal radii, central corneal thickness, asphericity, and the predicted effective lens position. A central issue is that most conventional 3rd generation formulas estimate lens position amongst other parameters on keratometry, which is altered in post-LVC eyes. CONCLUSION: An IOL power calculation results in eyes with prior LVC that are notably impaired in eyes without prior surgery. Effective corneal power including anterior corneal curvature, posterior corneal curvature, CCT (central corneal thickness), and asphericity is essential. Total keratometry in combination with the Barrett True-K, EVO (emmetropia verifiying optical formula), or Haigis formula is relatively uncomplicated and seems to provide good results, as does the Barrett True-K formula with anterior K values. The ASCRS ( American Society of Cataract and Refractive Surgery) calculator combines results of various formulae and averages results, which allows a direct comparison between the different methods. Tomography-based raytracing and the Kane and the Castrop formulae need to be evaluated by future studies.

Corneal riboflavin gradients and UV-absorption characteristics after topical application of riboflavin in concentrations ranging from 0.1 to 0.5.

Avoiding damage of the endothelial cells, especially in thin corneas, remains a challenge in corneal collagen crosslinking (CXL). Knowledge of the riboflavin gradients and the UV absorption characteristics after topical application of riboflavin in concentrations ranging from 0.1% to 0.5% could optimize the treatment. In this study, we present a model to calculate the UV-intensity depending on the corneal thickness. Ten groups of de-epithelialized porcine corneas were divided into 2 subgroups. Five groups received an imbibition of 10 min and the other five groups for 30 min. The applied riboflavin concentrations were 0.1%, 0.2%, 0.3%, 0.4% and 0.5% diluted in a 15% dextran solution for each subgroup. After the imbibition process, two-photon fluorescence microscopy was used to determine fluorescence intensity, which was compared to samples after saturation, yielding the absolute riboflavin concentration gradient of the cornea. The extinction coefficient of riboflavin solutions was measured using a spectrophotometer. Combining the obtained riboflavin concentrations and the extinction coefficients, a depth-dependent UV-intensity profile was calculated for each group. With increasing corneal depth, the riboflavin concentration decreased for all imbibition solutions and application times. The diffusion coefficients of 10 min imbibition time were higher than for 30 min. A higher RF concentration and a longer imbibition time resulted in higher UV-absorption and a lower UV-intensity in the depth of the cornea. Calculated UV-transmission was 6 percentage points lower compared to the measured transmission. By increasing the riboflavin concentration of the imbibition solution, a substantially higher UV-absorption inside the cornea is achieved. This offers a simple treatment option to control the depth of crosslinking e.g. in thin corneas, resulting in a lower risk of endothelial damage.

Cellular Factor XIII, a Transglutaminase in Human Corneal Keratocytes.

Cellular factor XIII (cFXIII, FXIII-A2), a transglutaminase, has been demonstrated in a few cell types. Its main function is to cross-link proteins by isopeptide bonds. Here, we investigated the presence of cFXIII in cells of human cornea. Tissue sections of the cornea were immunostained for FXIII-A in combination with staining for CD34 antigen or isopeptide cross-links. Isolated corneal keratocytes were also evaluated by immunofluorescent microscopy and flow cytometry. FXIII-A in the corneal stroma was quantified by Western blotting. FXIII-A mRNA was detected by RT-qPCR. The cornea of FXIII-A-deficient patients was evaluated by cornea topography. FXIII-A was detected in 68 ± 13% of CD34+ keratocytes. Their distribution in the corneal stroma was unequal; they were most abundant in the subepithelial tertile. cFXIII was of cytoplasmic localization. In the stroma, 3.64 ng cFXIII/mg protein was measured. The synthesis of cFXIII by keratocytes was confirmed by RT-qPCR. Isopeptide cross-links were detected above, but not within the corneal stroma. Slight abnormality of the cornea was detected in six out of nine FXIII-A-deficient patients. The presence of cFXIII in human keratocytes was established for the first time. cFXIII might be involved in maintaining the stability of the cornea and in the corneal wound healing process.

Bacterial and Fungal Keratitis: A Retrospective Analysis at a University Hospital in Switzerland.

BACKGROUND: Infectious keratitis is a serious corneal disease and may lead to permanent visual deterioration if not treated rapidly and effectively. In order to determine possible changes in the spectrum of pathogens over time, we evaluated the pathogenic organisms of keratitis at a university hospital in Switzerland, comparing two time periods within a decade. METHODS: In this retrospective study, 417 patients with the clinical diagnosis of bacterial or fungal keratitis in 2006/07 and 2015/16 were enrolled. In an additional analysis, all cases of fungal keratitis between 2006 and 2016 were evaluated. Collected parameters were age, gender, side, use of contact lenses, systemic, neurological and ocular diseases, trauma, previous surgery, and systemic and topical therapy before presentation. In each patient, microbiological results of corneal smears such as growth and antibiotic resistance were analysed. RESULTS: A total of 163 and 254 eyes were included in 2006/07 and 2015/16, respectively. In 2006/07, a culture of smears revealed a bacterial cause in 70 eyes (42.9%) and a fungal cause in 4 eyes (2.5%), whereas in 2015/16, bacterial growth was found in 115 eyes (45.3%) and fungal growth in 6 eyes (2.4%). The most common bacteria in 2006/07 and 2015/16 were coagulase-negative Staphylococci (44.3 vs. 49.6%), Pseudomonas aeruginosa (18.6 vs. 13.9%), Staphylococcus aureus (10 vs. 16.5%), Corynebacterium spp. (8.6 vs. 5.2%), and Moraxella spp. (7.1 vs. 9.6%). Candida parapsilosis was the most common fungal isolate in both groups (25 vs. 33.3%). Between 2006 and 2016, fungal keratitis was found in 37 eyes (Candida spp. n = 11, Fusarium spp. n = 11, Aspergillus spp. n = 5, others n = 10). All patients with Fusarium spp. keratitis had a history of wearing contact lenses. CONCLUSION: The most commonly isolated bacterial organisms were Staphylococci and Pseudomonas spp., whereas fungal keratitis was mainly due to Candida spp. or Fusarium spp. No relevant variation in causative pathogens was observed between the two time periods.

The influence of hydration on different mechanical moduli of the cornea.

PURPOSE: To determine the interrelation of different elastic moduli of the cornea and to investigate their dependency on corneal hydration. METHODS: Rabbit eyes were divided into four groups. Corneas were excised and mounted into a Barron artificial anterior chamber. Various corneal hydration steady states were achieved with different dextran T-500 concentrations in the anterior chamber, as well as on the corneal anterior surface. The treatment-solutions of each group contained either 5, 10, 15, or 20% w/w dextran. Ultrasound pachymetry was used to measure central corneal thickness. Brillouin microscopy of the central cornea determined the longitudinal bulk modulus by means of Brillouin frequency shift. Subsequently, a 5-mm-wide central strip was taken for extensiometry to measure the tangential elastic modulus. RESULTS: The longitudinal bulk modulus was 1.2-times higher in corneas dehydrated with 20% dextran compared to those hydrated with 5% dextran. In contrast, the tangential elastic modulus increased by 4.4 times. The obtained longitudinal bulk moduli were two orders of magnitude bigger than the tangential elastic moduli. Regression analysis of longitudinal bulk modulus and tangential elastic modulus revealed a quadratic relation. The bulk modulus seemed to be independent of tension, whereas the elastic modulus was tension-dependent. Greater corneal hydration led to significantly thicker pachymetry. CONCLUSION: Corneal biomechanics are highly dependent on the level of corneal hydration. Surprisingly, tangential elastic moduli were more sensitive to hydration changes than longitudinal bulk moduli. A quadratic relation was found between both moduli.

Corneal crosslinking (CXL) with 18-mW/cm2 irradiance and 5.4-J/cm2 radiant exposure-early postoperative safety.

PURPOSE: To investigate safety of accelerated corneal crosslinking during the first postoperative month. METHODS: In this retrospective study, 76 eyes of 60 patients with verified progressive keratectasia were enrolled in this study and followed for 1 month after accelerated CXL (18 mW/cm2 for 5 min, radiant exposure 5.4 J/cm2) (A-CXL(5*18)). Preoperatively, objective refraction, slit lamp inspection, and corneal tomography were performed. Early postoperative slit lamp examinations were performed on days 1 and 4. At 1 month, objective refraction, slit lamp inspection, and corneal tomography were performed. RESULTS: Gender distribution was m:f = 55:21, OD:OS was 40:36, and the average age was 26.5 ± 8.6 years at surgery. Only 71 of the 76 eyes completed the 1-month follow-up, indicating a dropout rate of 6.6%. In 7.0% (n = 5), sterile infiltrates were observed; 5.6% of eyes (n = 4) showed delayed epithelial healing (> 4 days) in 2.8% (n = 2); an infection occurred and in 1 eye (1.4%), a stromal scar was detected; no other complications, neither a loss of two or more Snellen lines at 1 month postoperatively, were observed. As a risk factor for sterile infiltrates, thin preoperative pachymetry could be identified (p = 0.027). CONCLUSIONS: This study revealed no difference in early postoperative safety between CXL using 18 mW/cm2 and standard corneal CXL. Thinner preoperative pachymetry could be identified predicting a higher rate of postoperative sterile infiltrates.

Corneal collagen cross-linking for Terrien marginal degeneration.

PURPOSE: To report the long-term clinical outcome of a patient diagnosed as having Terrien marginal degeneration (TMD) who was subjected to corneal collagen cross-linking (CXL) with ultraviolet-A and riboflavin in both eyes. METHODS: Topographical changes were assessed by high-resolution Scheimpflug imaging and anterior segment optical coherence tomography. Eccentric epithelium-off CXL was performed in both eyes while protecting the corneal limbus. Irradiation was performed with a fluence of 5.4 J/cm(2), using 3 mW/cm(2) for 30 minutes. RESULTS: Five years of postoperative follow-up showed regression of the keratometric values, a local thickening of the corneal stroma, and bilateral improvement of corrected distance visual acuity. CONCLUSIONS: CXL may arrest progression in TMD and even reverse the catabolic process in the corneal stroma. CXL might represent an alternative therapeutic approach for the management of TMD.

Hyperbaric Oxygenation Maintains Elevated Stromal Oxygen Availability During Corneal Collagen Crosslinking with and Without Epithelial Removal.

PURPOSE: Corneal collagen cross-linking (CXL) can halt corneal ectasia. Leaving corneal epithelium intact during treatment may reduce the incidence of complications. However, it is under debate whether this reduces efficacy and if oxygen supplementation may be necessary to optimize the cross-linking effect. This study aimed to investigate the impact of hyperbaric oxygenation (HBO) on intracorneal oxygen concentrations during epi-off and epi-on CXL. METHODS: CXL was performed using riboflavin and ultraviolet-A (UV-A) irradiance (3 mW/cm2 for 30 min) on porcine corneas under normobaric and hyperbaric conditions, with and without supplemented oxygen, with and without epithelium. Intracorneal oxygen concentrations were continuously monitored before and during irradiation. Biomechanical properties were assessed through tensile strength testing. RESULTS: HBO alone did not cause perceivable changes in stromal oxygen concentrations. Oxygen supplementation resulted in higher oxygen concentration in corneal stroma during CXL. HBO may cause a further increase in oxygen levels, although this was not statistically significant in this study. Notably, a tendency of oxygen levels to rise continuously during UV-irradiation was observed using HBO. Biomechanical properties showend no statistically significant differences between any groups. CONCLUSIONS: In this ex-vivo model, HBO increased stromal oxygen levels during CXL, regardless of the presence of corneal epithelium. The dynamics in oxygen concentrations in corneal stromal tissue during CXL suggest that time is an important factor to consider in modifications of established protocols. Also, we hypothesize that stromal levels of riboflavin and UV-A irradiance may be more critical to the CXL effect when oxygen is supplemented and epithelium is not removed.

The Influence of Lens Position, Vault Prediction, and Posterior Cornea on Phakic Posterior Chamber Intraocular Lens Power.

BACKGROUND: Achieving precise refractive outcomes in phakic posterior chamber intraocular lens (pIOL) implantation is crucial for patient satisfaction. This study investigates factors affecting pIOL power calculations, focusing on myopic eyes, and evaluates the potential benefits of advanced predictive models. DESIGN: Retrospective, single-center, algorithm improvement study. METHODS: Various variations with different effective lens position (ELP) algorithms were analyzed. The algorithms included a fixed constant model, and a multiple linear regression model and were tested with and without incorporation of the posterior corneal curvature (Rcp). Furthermore, the impact of inserting the postoperative vault, the space between the pIOL and the crystalline lens, into the ELP algorithm was examined, and a simple vault prediction model was assessed. RESULTS: Integrating Rcp and the measured vault into pIOL calculations did not significantly improve accuracy. Transitioning from constant model approaches to ELP concepts based on linear regression models significantly improved pIOL power calculations. Linear regression models outperformed constant models, enhancing refractive outcomes for both ICL and IPCL pIOL platforms. CONCLUSIONS: This study underscores the utility of implementing ELP concepts based on linear regression models into pIOL power calculation. Linear regression based ELP models offered substantial advantages for achieving desired refractive outcomes, especially in lower to medium power pIOL models. For pIOL power calculations in both pIOL platforms we tested with preoperative measurements from a Scheimpflug device, we found improved results with the LION 1ICL formula and LION 1IPCL formula. Further research is needed to explore the applicability of these findings to a broader range of pIOL designs and measurement devices.

Differences Between Keratometry and Total Keratometry Measurements in a Large Dataset Obtained With a Modern Swept Source Optical Coherence Tomography Biometer.

PURPOSE: This study aimed to explore the concept of total keratometry (TK) by analyzing extensive international datasets representing diverse ethnic backgrounds. The primary objective was to quantify the disparities between traditional keratometry (K) and TK values in normal eyes and assess their impact on intraocular lens (IOL) power calculations using various formulas. DESIGN: Retrospective multicenter intra-instrument reliability analysis. METHODS: The study involved the analysis of biometry data collected from ten international centers across Europe, the United States, and Asia. Corneal power was expressed as equivalent power and astigmatic vector components for both K and TK values. The study assessed the influence of these differences on IOL power calculations using different formulas. The results were analyzed and plotted using Bland-Altman and double angle plots. RESULTS: The study encompassed a total of 116,982 measurements from 57,862 right eyes and 59,120 left eyes. The analysis revealed a high level of agreement between K and TK values, with 93.98% of eyes exhibiting an absolute difference of 0.25 D or less. Astigmatism vector differences exceeding 0.25 D and 0.50 D were observed in 39.43% and 1.08% of eyes, respectively. CONCLUSIONS: This large-scale study underscores the similarity between mean K and TK values in healthy eyes, with rare clinical implications for IOL power calculation. Noteworthy differences were observed in astigmatism values between K and TK. Future investigations should delve into the practicality of TK values for astigmatism correction and their implications for surgical outcomes.

Comparison of Corneal Thickness Measurements After Customized Corneal Crosslinking Using High-Resolution Optical Coherence Tomography and Scheimpflug Tomography.

PURPOSE: The aim of this study was to compare the evolution of corneal pachymetry after customized corneal crosslinking (CXL) between Scheimpflug-based and optical coherence-based corneal tomography (OCT). METHODS: In this retrospective study, central corneal thickness (CCT), thinnest corneal thickness, and epithelial thickness of 33 eyes of 33 patients with keratoconus were measured preoperatively and 1, 3, and 12 months after customized CXL using the Pentacam HR and the MS-39. The mean pachymetry values of measurements were compared with a paired sample t test. Bland-Altman plots and 95% limits of agreement (LoA) were used to assess the agreement between the measurements of the 2 devices. RESULTS: The mean age of the participants was 29.7 ± 11.4 years. At baseline, the mean CCT measurements were equal with Pentacam HR (478.30 ± 36.77 µm) and MS-39 (478.46 ± 38.01 µm). After CXL, CCT obtained by Pentacam HR was 460.65 ± 38.69 µm, 464.65 ± 44.45 µm, and 476.77 ± 39.85 µm, and by MS-39 was 478.18 ± 39.50 µm, 472.89 ± 40.92 µm, and 479.51 ± 39.20 µm at 1, 3, and 12 months, respectively. Pentacam HR measured significantly lower CCT ( P < 0.05) at months 1 and 3 after CXL. The agreement was smallest between both devices at month 1 (95% LoA -59 to 24 µm) followed by month 3 (95% LoA: -41 to 23 µm). Epithelial thickness, measured with OCT alone, increased significantly at 1 month and regained preoperative levels at 3 months and thereafter. CONCLUSIONS: After CXL, corneal pachymetry significantly differs between OCT-based and Scheimpflug-based corneal tomography. Pentacam HR seems to underestimate pachymetry when haze is present.