[Deep anterior lamellar keratoplasty in extrusion of an incomplete intrastromal corneal ring segment (clinical observation)]. / Glubokaya perednyaya posloinaya keratoplastika pri ekstruzii nepolnogo intrastromal'nogo kol'tsa (klinicheskoe nablyudenie).

Intrastromal corneal ring segments (ICRS) of in various shapes are used to correct structural changes in the cornea and improve visual acuity in keratoconus (KC). The most serious complications of the technology infection, vascular ingrowth, and extrusion. In this study a 44-year-old patient underwent deep anterior lamellar keratoplasty (DALK) 5 years after implantation of ICRS in the shape of an incomplete ring to treat its extrusion of up to 30%, vascular ingrowth into the cornea and corneal syndrome. The following DALK technique was used: excision of the free part of the corneal segment, removal of the remaining part of the corneal segment, excision of 80% of thickness of the corneal block with a 8.5-mm trepan, pneumatic dissection of the stroma down to the Descemet membrane (DM), removal of the remaining stroma on the viscoelastic pillow, laying and suture fixation of the donor graft. There were no complications during the postoperative period, the graft remained transparent for up to 10 months. Uncorrected visual acuity (UCVA) increased from 0.01 to 0.4, best corrected visual acuity (BCVA) increased from 0.3 to 0.7. The number of endothelial cells decreased from 2980 to 2670 cells/mm2 (10.4%). This clinical case demonstrates that DALK surgery can be a reliable method of patient rehabilitation in cases of extrusion of ICRS in the shape of an incomplete ring and vascular ingrowth.

Quantifying Corneal Topographic Astigmatism (CorT Total) in Keratoconic Eyes.

PURPOSE: To determine optimal corneal regions from which to derive corneal topographic astigmatism (CorT) in kerato-conic eyes. METHODS: In this retrospective study, potential measures of corneal astigmatism are calculated from raw total corneal power data (179 eyes from 124 patients) from a corneal tomographer. The measures are derived from annular corneal regions varying in both extent and center position, and evaluated according to the variability of the ocular residual astigmatism (ORA) in the cohort. This variability is quantified by the ORArms, which is the root-mean-squared distance of the ORAs from their summated vector mean in double angle space. The lower the ORArms, the better the corneal astigmatism measure corresponds to manifest refractive cylinder. RESULTS: Corneal astigmatism measures derived from regions centered on corneal vertex had ORArms values (mild: 1.07 diopters [D], moderate: 1.61 D, severe: 2.65 D) as low or lower than other measures derived from regions centered on thinnest point, corneal apex (front or back), or pupil center. Corneal astigmatism measures derived from a region centered 30% of the way toward thinnest point from corneal vertex appeared to have even lower ORArms values (mild: 1.05 D, moderate: 1.45 D, severe: 2.56 D). None of the corneal astigmatism measures corresponded closely with manifest refractive cylinder for severe keratoconus (ORArms > 2.50 D). CONCLUSIONS: For keratoconic eyes, the CorT should be derived from an annular region centered 30% of the way toward thinnest point from corneal vertex, although when the keratoconus is mild, a standard corneal-vertex-centered CorT performs just as well. [J Refract Surg. 2023;39(3):206-213.].

Laser in situ keratomileusis versus Artisan lens implantation in correcting ametropia after penetrating keratoplasty for keratoconus.

PURPOSE: To compare the long-term safety and efficacy of laser in situ keratomileusis (LASIK) with Artisan phakic intraocular lens implantation to correct refractive errors after penetrating keratoplasty (PK) for keratoconus. METHODS: This retrospective comparative interventional case series included a total of 33 consecutive keratoconus eyes that had previous PK and received subsequent LASIK (n = 16) or Artisan lens implantation (n = 17) were included in this study. Outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive error, and complications. RESULTS: Postoperatively, the UDVA of ≥20/40 was achieved in none of the LASIK group compared to 62.5% of eyes in the Artisan group (P < 0.001); the respective values for CDVA of ≥20/40 were 87.5 and 94.1% (P = 0.51). Spherical equivalent refraction decreased from - 6.97 ± 1.50 D preoperatively to - 4.20 ± 2.05 D postoperatively in the LASIK group (P < 0.001) and from - 10.79 ± 2.15 D preoperatively to - 2.13 ± 1.23 D postoperatively in the Artisan group (P < 0.001). There was no significant change in the refractive astigmatism in LASIK group (P = 0.30) or Artisan group (P = 0.11). The efficacy and safety indices were significantly better for Artisan (0.82 ± 0.34 and 1.13 ± 0.30, respectively) than for LASIK (0.22 ± 0.17 and 0.85 ± 0.24, respectively, P ≤ 0.006 for both comparisons). While refractive error changed significantly from postoperative year 3 to the final visit in the LASIK group, it remained stable in the Artisan group through follow-up period. No significant complications were observed in any group. CONCLUSION: Artisan lens implantation provided superior and stable visual outcomes compared to LASIK for the management of post PK refractive errors in keratoconus eyes.

Antioxidant and Anti-Inflammatory Effects of Oral Supplementation with a Highly-Concentrated Docosahexaenoic Acid (DHA) Triglyceride in Patients with Keratoconus: A Randomized Controlled Preliminary Study.

A prospective, randomized, single-center preliminary study was performed in patients with keratoconus stages I-III (Amsler-Krumeich), who received a high rich docosahexaenoic acid (DHA) (1000 mg/day) supplement for 3 months versus untreated patients. One eye per patient was evaluated. Thirty-four patients were recruited (75% men, mean age 31 years), with 15 randomized to the control group and 19 to the DHA-treated group. Corneal topography variables and plasma biomarkers of oxidative stress and inflammatory status were evaluated. A panel of fatty acids in blood samples was also assessed. There were significant between-group differences in the astigmatism axis, asphericity coefficient, and intraocular pressure in favor of the DHA group. Additionally, between-group significant differences in total antioxidant capacity (TAC), malondialdehyde (MDA), free glutathione (GSH) and GSH/GSSG ratio, as well as reduced values of inflammatory markers, including interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF-A) were found. These preliminary findings support the usefulness of the antioxidant and anti-inflammatory effects of DHA supplementation for targeting underlying pathophysiological mechanisms of keratoconus. Prolonged duration of DHA supplementation may be needed to detect more noticeable clinical changes in corneal topography.

Distribution of corneal densitometry in different grades of keratoconus.

Purpose: To evaluate the use of Scheimpflug tomography in corneal densitometry (CD) in comparing the stages of keratoconic eyes. Methods: Keratoconic (KC) corneas (stages 1-3 classified according to the topographic parameters) were examined using the Scheimpflug tomographer (Pentacam, Oculus) using the CD software. CD was measured over three different depths (anterior stromal layer [120 µm], posterior stromal layer [60 µm], and middle stromal layer between these two layers), and concentric annular zones (0.0 to 2.0, 2.0 to 6.0, 6.0 to 10.0, and 10.0 to 12.0 mm diameter area). Results: The study participants were divided into three groups: keratoconus (KC) stage 1 (KC1) with 64 participants, keratoconus stage 2 (KC2) with 29 participants, and keratoconus stage 3 (KC3) with 36 participants. Comparing CD of all three layers (anterior, central, and posterior) of the cornea over different circular annuli (0-2, 2-6, 6-10, and 10-12 mm) revealed a significant difference in the 6-10 mm annulus between all groups and in all layers (P = 0.3, 0.2, and 0.2, respectively). Area under curve (AUC) was done. It revealed that the central layer showed the highest specificity (93.8%) in comparing KC1 and KC2, whereas CD in the anterior layer between KC2 and KC3 had the highest specificity (86.2%). Conclusion: CD showed increased values in the anterior corneal layer and in the annulus 6-10 mm more than other locations in all stages of KC.

Virtual keratoconus monitoring clinic in a tertiary university hospital in the United Kingdom.

Purpose: To describe a new pathway for virtual keratoconus (KC) monitoring in the corneal department of a tertiary referral center in the UK during the coronavirus disease 2019 (COVID-19) pandemic. Methods: A virtual outpatient clinic to monitor KC patients (KC PHOTO clinic) was created. All patients from the KC database in our department were included. At each hospital visit, patients' visual acuity and tomography (Pentacam; Oculus, Wetzlar, Germany) were collected by a health-care assistant and an ophthalmic technician, respectively. The results were virtually reviewed by a corneal optometrist to identify stability or progression of KC and discussed with a consultant if needed. Those with progression were contacted by telephone and listed for corneal crosslinking (CXL). Results: From July 2020 until May 2021, 802 patients were invited to attend the virtual KC outpatient clinic. Of them, 536 patients (66.8%) attended and 266 (33.2%) did not attend. After corneal tomography analysis, 351 (65.5%) were stable, 121 (22.6%) showed no definite evidence of progression, and 64 (11.9%) showed progression. Forty-one (64%) patients with progressive KC were listed for CXL and the remaining 23 patients deferred treatment after the pandemic. By converting a face-to-face clinic to a virtual clinic, we were able to increase our capacity by nearly 500 appointments per year. Conclusion: In pandemic times, hospitals have developed novel methods of delivering safe patient care. KC PHOTO is a safe, effective, and innovative method of monitoring KC patients and diagnosing progression. In addition, virtual clinics can increase the clinic capacity tremendously and reduce the need of face-to-face appointments, which is beneficial in pandemic conditions.

Corneal bacterial microbiome in patients with keratoconus using next-generation sequencing-based 16S rRNA gene analysis.

PURPOSE: To investigate the corneal bacterial microbiome in patients with keratoconus using next-generation sequencing and develop a new perspective on the pathogenesis of the disease. METHODS: This prospective observational study included 10 patients with keratoconus who underwent corneal crosslinking procedure and 10 healthy controls who underwent photorefractive keratectomy. Patients included in the study were aged 18 years or older. The demographic and clinical characteristics of participants were recorded. Corneal epithelial samples were collected between March 2021 and June 2021. Isolated bacterial DNA from corneal epithelial samples was analyzed using 16 S ribosomal RNA gene analysis. The relative abundance rates at the phylum and genus levels were calculated. Alpha diversity parameters were assessed. RESULTS: Eleven phyla and 521 genera of bacteria were identified in all participants. At the phylum level, Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes were most abundant in both groups. There were no statistical differences between the two groups except Bacteriodetes (p < 0.05). At the genus level, the relative abundance rates of twenty bacteria were significantly different between keratoconus and healthy corneas (p < 0.05). Aquabacterium was the most abundant genus in patients with keratoconus, while Shigella was the most abundant genus in healthy controls. Alpha diversity parameters were lower in patients with keratoconus, although the difference did not reach statistical significance (p > 0.05). CONCLUSIONS: Our preliminary study revealed that there are similarities and differences in the corneal microbiome between keratoconus and healthy individuals. Further research is required on the relationship between the abnormal corneal microbiome composition and the pathogenesis of keratoconus.

The Impaired Wound Healing Process Is a Major Factor in Remodeling of the Corneal Epithelium in Adult and Adolescent Patients With Keratoconus.

Purpose: Keratoconus (KTCN) is the most common corneal ectasia, characterized by pathological cone formation. Here, to provide an insight into the remodeling of the corneal epithelium (CE) during the course of the disease, we evaluated topographic regions of the CE of adult and adolescent patients with KTCN. Methods: The CE samples from 17 adult and 6 adolescent patients with KTCN, and 5 control CE samples were obtained during the CXL and PRK procedures, respectively. Three topographic regions, central, middle, and peripheral, were separated toward RNA sequencing and MALDI-TOF/TOF Tandem Mass Spectrometry. Data from transcriptomic and proteomic investigations were consolidated with the morphological and clinical findings. Results: The critical elements of the wound healing process, epithelial-mesenchymal transition, cell-cell communications, and cell-extracellular matrix interactions were altered in the particular corneal topographic regions. Abnormalities in pathways of neutrophils degranulation, extracellular matrix processing, apical junctions, IL, and IFN signaling were revealed to cooperatively disorganize the epithelial healing. Deregulation of the epithelial healing, G2M checkpoints, apoptosis, and DNA repair pathways in the middle CE topographic region in KTCN explains the presence of morphological changes in the corresponding doughnut pattern (a thin cone center surrounded by a thickened annulus). Despite similar morphological characteristics of CE samples in adolescents and adults with KTCN, their transcriptomic features were different. Values of the posterior corneal elevation differentiated adults with KTCN from adolescents with KTCN and correlated with the expression of TCHP, SPATA13, CNOT3, WNK1, TGFB2, and KRT12 genes. Conclusions: Identified molecular, morphological, and clinical features indicate the effect of impaired wound healing on corneal remodeling in KTCN CE.

Evaluation of Corneal Parameters and Meibomian Gland Alterations After Corneal Cross-Linking in Patients With Progressive Keratoconus.

OBJECTIVES: The aim of the study was to evaluate the changes in corneal parameters and meibomian gland alterations after corneal cross-linking (CXL) for progressive keratoconus. METHODS: Thirty nine eyes of 39 keratoconus patients were treated with CXL. Corneal topography, specular microscopy, the Ocular Surface Disease Index© (OSDI), noninvasive tear break-up time (NITBUT), and meibography indices were evaluated preoperatively and at the first, third, and sixth months after CXL. RESULTS: The flattest keratometry (K1) ( P =0.003), steepest keratometry (K2) ( P <0.001), apex, central, and thinnest corneal thicknesses ( P <0.001) showed significant differences after cross-linking, whereas the changes in the maximum keratometry (Kmax) were not significant ( P =0.140). The endothelial cell density, coefficient of variation, and hexagonality were unchanged. The NITBUT values decreased after cross-linking; however, there was no significant change in OSDI index ( P =0.313), meiboscore ( P =0.392), and meibomian gland loss degrees ( P =0.300). No change was detected in the morphology of the meibomian glands after CXL. CONCLUSION: In eyes with keratoconus, a flattening in keratometry readings and thinning in corneal thickness were observed after CXL. The corneal endothelium is protected by dextran-free riboflavin. Cross-linking procedure causes dry eye by changing the corneal structure without affecting the morphology of the meibomian glands.

Comparison of Ocular Wavefront Aberration Measurements Obtained Using Two Hartmann-Shack Wavefront Aberrometers.

OBJECTIVES: To assess agreement between measurements of ocular wavefront aberrations obtained using the Pentacam AXL Wave (Oculus Optikgeräte GmbH) (Aberrometer A) and KR-1W (Topcon Corp) (Aberrometer B), both of which are based on the Hartmann-Shack principle. METHODS: In this prospective case-control study, ocular wavefront aberrations measurements were obtained using both aberrometers in patients with keratoconus (KC) and control participants. Ocular wavefront aberrations were measured through the natural pupil without dilation using both devices in a dark room. For both aberrometers, accommodation was inhibited by automatically adding fogging. The individual Zernike coefficients from the second to fourth order were compared between the two aberrometers for a 4-mm pupil diameter. RESULTS: Twenty-six KC and 29 control eyes were assessed. Statistically significant correlations ( P <0.05) were observed for all Zernike coefficients, except for Z 4-2 in the control group. Bland-Altman analysis indicated good agreement between aberrometers and no statistically significant differences in the control group. However, in the KC group, patterns of proportional error were observed in vertical coma Z 3-1 (r=0.338, P =0.008), trefoil Z 4-4 (r=0.701, P =0.003), secondary astigmatism Z 4-2 (r=0.348, P =0.025), and spherical aberrations Z 40 (r=0.407, P =0.012). CONCLUSIONS: The Zernike coefficient values measured by the two aberrometers were well correlated in the control and KC groups. However, in eyes with KC, Aberrometer B tended to present greater values in several Zernike coefficients than Aberrometer A, suggesting that wavefront measurements obtained using the two aberrometers are not interchangeable in patients with KC.

Características clínico-epidemiológicas del queratocono en Asturia / Clinical-epidemiological characteristics of keratoconus in Asturias

Introducción El queratocono es la ectasia corneal más frecuente y la segunda causa de queratoplastia en el mundo. Las características clínicas y epidemiológicas del queratocono no han sido apenas estudiadas en España y, hasta la fecha, no se ha hecho ningún trabajo en Asturias. Material y métodos Se realizó un estudio transversal analizando todos los casos de queratocono diagnosticado en las primeras consultas de la sección de Córnea y Superficie de los centros Hospital Universitario Central de Asturias (Oviedo) y Hospital Universitario de Cabueñes (Gijón) entre 2017 y 2020. A todos los pacientes se les recogieron datos demográficos, agudeza visual y se les realizó una topografía corneal. Resultados Se incluyeron un total de 112 pacientes (42,0% mujeres y 58,0% hombres). La edad media era de 36,84±15,59, teniendo un 39,3% una edad superior a 40 años. Un 31,8; 28,0; 15,0 y 25,2% se encontraban en los estadios i, ii, iii y iv, respectivamente, en la escala Amsler-Krumeich. En un 7,5% se implantaron segmentos corneales, en un 4,7% se realizó cross-linking y en un 13,2% se realizó queratoplastia. Conclusión Aproximadamente un 40% de los queratoconos se detectan en estadios avanzados y otro 40% a una edad superior a los 40 años. Un 13% de los mismos requieren queratoplastia, por lo que sigue siendo una indicación frecuente en nuestro medio. Es necesario, por tanto, realizar un diagnóstico precoz para actuar antes de que exista una pérdida visual irreversible. (AU)

Introduction Keratoconus is the most frequent corneal ectasia and second most common cause of keratoplasty worldwide. The clinical and epidemiological characteristics of keratoconus have rarely been studied in Spain, and to date, no study has been done in Asturias. Material and methods A cross-sectional study was conducted to analyze all cases of keratoconus diagnosed in the first consultations of the cornea and surface section of the Hospital Universitario Central de Asturias (Oviedo) and Hospital Universitario de Cabueñes (Gijón) between 2017 and 2020. Demographic data, visual acuity and corneal topography were collected. Results A total of 112 patients (42.0% women and 58.0% men) were included. The mean age was 36.84±15.59, with 39.3% being older than 40 years. 31.8%, 28.0%, 15.0%, and 25.2% were in stages i, ii, iii and iv, Amsler–Krumeich scale, respectively. Corneal segments were implanted in 7.5% of patients, cross-linking was performed in 4.7%, and keratoplasty was performed in 13.2%. Conclusion Approximately 40% of keratoconus cases are detected at advanced stages and another 40% are detected at an age over 40 years. 13% of these patients require keratoplasty, which is why it is frequently performed in our setting. Therefore, early diagnosis before irreversible visual loss is necessary. (AU)

Comparison of visual outcomes, keratometric parameters and biomechanical profiles between deep anterior lamellar keratoplasty with big-bubble technique vs. Melles technique for keratoconus: a retrospective study.

OBJECTIVE: Comparing results of two different DALK surgery techniques (big bubble vs. Melles) in patients with advanced keratoconus. DESIGN: a retrospective comparative clinical study. PARTICIPANTS: This study conducted on 72 eyes of 72 participants. INTRODUCTION: This study designed to compare the results of two different DALK surgery techniques (big bubble vs. Melles) in patients with advanced keratoconus. METHOD: Thirty-seven eyes were treated using the big bubble DALK method, while 35 eyes were treated using the Melles approach. Uncorrected visual acuity (UCVA), best corrected spectacle visual acuity (BCSVA), manifest refraction, keratometric characteristics, contrast sensitivity, corneal aberrations, corneal biomechanical characteristics, and endothelial cell profile are the outcome measurements. RESULTS: Mean UCVA in big bubble group was 0.61 ± 25 LogMAR and in Melles group was 0.89 ± 0.41 LogMAR (p-value 0.043). Mean BCSVA in big bubble group (0.18 ± 0.12 Log MAR) was significantly better than Melles group (0.35 ± 0.16 Log MAR). Mean of sphere and cylinder refraction showed no significant difference between two groups. Comparing the endothelial cell profile, corneal aberrations, corneal biomechanical properties and keratometry had no significantdifferences. Contrast sensitivity reported as modulation transfer function (MTF) showed higher values in big bubble group and differences with Melles group weresignificant. Results of point spread function (PSF) in big bubble group had superiority to Melles group with considerable statistical P value of 0.023. CONCLUSION: When opposed to the Melles approach, the big bubble technique generates a smooth interface with less stromal residue, which results in higher visual quality and contrast sensitivity.

Ophthalmic Manifestations of Arterial Tortuosity Syndrome: Case Series of Patient and Carriers.

PURPOSE: The aim of this study was to report the detailed ophthalmic findings in a young patient with genetically confirmed arterial tortuosity syndrome (ATS) and the findings in 8 family members who were carriers. METHODS: Nine members of the same Saudi family were assessed at King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, for ATS-related ocular changes after homozygosity for the pathogenic variant of SLC2A10 gene was confirmed in 1 member. All family members underwent complete ophthalmic examination, genetic testing, and corneal tomography at presentation and at 6-month follow-up. RESULTS: All ophthalmic features were manifested in our patient with ATS including schisis-like splitting of the stromal layer with greater peripheral thinning, pannus, deep posterior stromal opacities, myopia, high astigmatism, and keratoglobus. The ocular phenotype was also expressed in some carriers ranging from mild myopia to the full spectrum of corneal abnormalities associated with ATS. CONCLUSIONS: Our study provided further insights into the phenotype in both patients with ATS and carriers. Annual ophthalmic examination is warranted in both types of patients and must undergo from early life onward to detect progressive ectasia which may necessitate corneal crosslinking.

Biomechanics of keratoconus: Two numerical studies.

BACKGROUND: The steep cornea in keratoconus can greatly impair eyesight. The etiology of keratoconus remains unclear but early injury that weakens the corneal stromal architecture has been implicated. To explore keratoconus mechanics, we conducted two numerical simulation studies. METHODS: A finite-element model describing the five corneal layers and the heterogeneous mechanical behaviors of the ground substance and lamellar collagen-fiber architecture in the anterior and posterior stroma was developed using the Holzapfel-Gasser-Ogden constitutive model. The geometry was from a healthy subject. Its stroma was divided into anterior, middle, and posterior layers to assess the effect of changing regional mechanical parameters on corneal displacement and maximum principal stress under intraocular pressure. Specifically, the effect of softening an inferocentral corneal button, the collagen-based tissues throughout the whole cornea, or specific stromal layers in the button was examined. The effect of simply disorganizing the orthogonally-oriented posterior stromal fibers in the button was also assessed. The healthy cornea was also subjected to eye rubbing-like loading to identify the corneal layer(s) that experienced the most tensional stress. RESULTS: Conical deformation and corneal thinning emerged when the corneal button or the mid-posterior stroma of the button underwent gradual softening or when the collagen fibers in the mid-posterior stroma of the button were dispersed. Softening the anterior layers of the button or the whole cornea did not evoke conical deformation. Button softening greatly increased and disrupted the stress on Bowman's membrane while mid-posterior stromal softening increased stress in the anterior layers. Eye rubbing profoundly stressed the deep posterior stroma while other layers were negligibly affected. DISCUSSION: These observations suggest that keratoconus could be initiated, at least partly, by mechanical instability/damage in the mid-posterior stroma that then imposes stress on the anterior layers. This may explain why subclinical keratoconus is marked by posterior but not anterior elevation on videokeratoscopy.

Corneal Biomechanical Characteristics in Osteogenesis Imperfecta With Collagen Defect.

Purpose: To identify the characteristic corneal biomechanical properties of osteogenesis imperfecta (OI), and to compare the corneal biomechanical properties between OI and keratoconus. Methods: We included 46 eyes of 23 patients with OI, 188 eyes of 99 keratoconus patients, and 174 eyes of 92 normal controls to compare corneal biomechanical parameters between OI corneas, keratoconus, and normal controls by using Corneal Visualization Scheimpflug Technology (Corvis ST). Results: Patients with OI had significantly higher Corvis biomechanical index (CBI) (P < 0.001), higher tomographic and biomechanical index (TBI) (P = 0.040), lower Corvis Biomechanical Factor (CBiF) (P = 0.034), and lower stiffness parameter at first applanation (SP-A1) (P < 0.001) compared with normal controls. In contrast, OI group showed lower CBI (P < 0.001), lower TBI (P < 0.001), higher CBiF (P < 0.001), and higher SP-A1 (P = 0.020) than keratoconus group. Notably, the stress-strain index (SSI) was not significantly different between the OI and normal controls (P = 1.000), whereas keratoconus showed the lowest SSI compared with OI group (P = 0.025) and normal controls (P < 0.001). Conclusions: Although the corneal structures of OI patients are less stable and easier to deform as compared to those of the control group, there is no significant difference in material stiffness observed between the OI and normal controls. In contrast, the corneas of keratoconus showed not only lower structural stability and higher deformability but also lower material stiffness compared with those of OI cornea and normal controls. Translational Relevance: The biomechanical alterations are different between OI corneas and keratoconus.

Corneal thickness measurements with the RTVue, Casia-2, and Pentacam devices in patients with mild-to-moderate keratoconus: a comparative study.

BACKGROUND: To compare the characteristics of corneal thickness measurements among the RTVue, Casia-2, and Pentacam in patients with mild-to-moderate keratoconus. METHODS: We recruited 46 eyes of 46 patients diagnosed with mild-to-moderate keratoconus at our hospital between January and March 2022. The central corneal thickness (CCT) and thinnest corneal thickness (TCT) were measured using two optical coherence tomography (OCT) instruments (RTVue and Casia-2) and the more conventional Pentacam. Differences and correlations between the CCTs and TCTs, based on the device and influencing factors, were explored. RESULTS: The CCTs were highly consistent among the groups (p = 0.434) and correlated with one another (p < 0.001). The TCTs measured by OCTs were thinner than those measured by the Pentacam (p < 0.001); however, all three devices were highly correlated (p < 0.001). The thinnest point location measurements with RTVue and Casia-2 differed significantly from the measurements with the Pentacam. Bland-Altman plots demonstrated a significant agreement between Pentacam and OCTs in TCT measurement (p < 0.001); the 95% limits of agreement were - 3.1 µm to + 33.1 µm for Pentacam and RTVue and - 8.6 µm to + 36.5 µm for Pentacam and Casia-2. RTVue and Casia-2 showed no difference in corneal thickness (p = 0.633) and thinnest point location measurement (p > 0.05). Multivariate analysis identified that the TCT measurement difference between the RTVue and Pentacam was related to the difference between the CCT and TCT (b = 0.490, 95% confidence interval [CI]: 0.033 to 0.948, p = 0.036), whereas the difference between the Casia-2 and Pentacam was related to the anterior radius for curvature (A) grade (b = 3.9, 95% CI: 1.753 to 6.074, p = 0.001), corneal pachymetry at the thinnest (C) grade (b = - 7.875, 95% CI: - 11.404 to - 4.346, p < 0.001), and the difference between the CCT and TCT (b = 0.425, 95% CI: 0.1 to 0.751, p = 0.012). CONCLUSIONS: CCTs in patients with mild-to-moderate keratoconus were similar among all three devices, but the TCTs and the thinnest point locations were not. Furthermore, the TCT measurement differences between the OCT devices and the Pentacam were more pronounced in keratoconus cases with a steeper anterior surface, thicker TCTs, and a larger difference between the CCT and TCT. TRIAL REGISTRATION: Number: 2021118-1. Retrospectively registered: September 01, 2021.

In-vivo high-speed biomechanical imaging of the cornea using Corvis ST and digital image correlation.

In-vivo corneal biomechanical characterization has gained significant clinical relevance in ophthalmology, especially in the early diagnosis of eye disorders and diseases (e.g. keratoconus). In clinical medicine, the air-puff-based tonometers such as Ocular Response Analyzer (ORA) and Corvis ST have been used in the in-vivo biomechanical testing. In the test, the high-speed dynamic deformation of the cornea under air-puff excitation is analyzed to identify the abnormities in the morphological and biomechanical properties of the cornea. While most existing measurements reflect the overall corneal biomechanical properties, in-vivo high-speed strain and strain rate fields at the tissue level have not been assessed. In this study, 20 subjects were classified into two different groups: the normal (NORM, N = 10) group and the keratoconus (KC, N = 10) group. Image sequences of the horizontal cross-section of the human cornea under air puff were captured by the Corvis ST tonometer. The macroscale mechanical response of the cornea was determined through image analysis. The high-speed evolution of full-field corneal displacement, strain, velocity, and strain rate was reconstructed using the incremental digital image correlation (DIC) approach. Differences in the parameters between the NORM and KC groups were statistically analyzed and compared. Statistical results indicated that compared with the NORM group, the KC corneas absorbed more energy (KC: 8.98 ± 2.76 mN mm; NORM: 4.79 ± 0.62 mN mm; p-value <0.001) with smaller tangent stiffness (KC: 22.49 ± 2.62 mN/mm; NORM: 24.52 ± 3.20 mN/mm; p-value = 0.15) and larger maximum deflection (KC: 0.99 ± 0.07 mN/mm; NORM: 0.92 ± 0.06 mN/mm; p-value <0.05) on the macro scale. Further, we also observed that The maximum displacement (KC: 1.17 ± 0.06 mm; NORM: 1.06 ± 0.07 mm; p-value <0.005), velocity (KC: 236 ± 29 mm/s; NORM: 203 ± 17 mm/s; p-value <0.01), shear strain (KC: 24.43 ± 2.59%; NORM: 20.26 ± 1.54%; p-value <0.001), and shear strain rate (KC: 69.74 ± 11.99 s-1; NORM: 54.84 ± 3.03 s-1; p-value <0.005) in the KC group significantly increased at the tissue level. This is the first time that the incremental DIC method was applied to the in-vivo high-speed corneal deformation measurement in combination with the Corvis ST tonometer. Through the image registration using incremental DIC analysis, spatiotemporal dynamic strain/strain rate maps of the cornea can be estimated at the tissue level. This is constructive for the clinical recognition and diagnosis of keratoconus at a more underlying level.