Renato Ambrósio

Purpose: To test whether the residual between ray-traced total corneal astigmatism and the vector sum of the anterior and posterior second-order astigmatic components is an independent, disease-related signal or a proportionally conserved feature of corneal thick-lens optics. Methods: Secondary analysis of a deidentified multicenter database of unoperated eyes examined with Pentacam HR and Corvis ST, restricted to clinically normal eyes and bilateral keratoconus, one eye per subject (1,680 normal; 1,181 keratoconic). Second-order Zernike astigmatic vectors were extracted over a 6.0 mm zone for the anterior (F) and posterior (B) surfaces and the ray-traced total cornea (T). The primary endpoint was the non-summation magnitude |T−F−B|. Pre-specified secondary analyses normalized the residual to total and anterior astigmatism, examined meridional-axis behavior, and tested associations with dynamic corneal response and composite indices. A sensitivity analysis added very asymmetric ectasia eyes. Results: Absolute non-summation was greater in keratoconic than in normal eyes (median 0.223 vs 0.155 µm; P < 0.001; Cliff's δ = 0.225, a small effect), but every astigmatic magnitude was scaled by a similar factor (anterior ×1.48, posterior ×1.28, total ×1.52, non-summation ×1.43). Within each group the residual was near-collinear with anterior astigmatism (Spearman ρ = 0.99), and its normalized fraction was essentially identical in normal and keratoconic eyes (median 0.149 vs. 0.147; Cliff's δ = −0.06) and in both eyes of patients with very asymmetric ectasia (0.147–0.149). Front–back meridional misalignment did not differ (5.89° vs. 5.63°; P = 0.49). Partial correlations with dynamic corneal response and composite indices, adjusted for astigmatism magnitude, were uniformly weak (| ρ | < 0.11). Conclusions: Corneal astigmatism is not fully described by vector summation of the two surfaces. The residual, compatible with thick-lens coupling and device-specific optical conventions, is larger in absolute terms in keratoconus but represents a constant proportion of each eye's astigmatism across the ectatic spectrum. We interpret it as a magnitude-coupled optical descriptor, not an independent diagnostic or biomechanical signal. Clinically, these findings caution against assuming direct additivity of the exported anterior and posterior astigmatic components; implications for toric and refractive planning require validation against clinically relevant optical outputs and postoperative outcomes. Future studies should model corneal and tear-film refractive-index effects explicitly.

Objective: To pay a scientific tribute to Dr. Yaron Rabinowitz by enhancing his PA/I-S index through machine learning-based predictive models using the Applied Artificial Intelligence (A²I) methodology. Methods: A retrospective study with 2,705 eyes (1,680 normal and 1,025 VAE) to develop a predictive model (AI Tribute) following the KDD knowledge discovery framework, whose performance was assessed in two clinical scenarios – Normal versus Clinical Ectasia (KC+VAE-E) (N=3,335) and Normal versus VAE-NT (N=2,231) – by AUC and the DeLong test. [...] ABSTRACT Objective: To pay a scientific tribute to Dr. Yaron Rabinowitz by enhancing his PA/I-S index through machine learning-based predictive models using the Applied Artificial Intelligence (A²I) methodology. Methods: A retrospective study with 2,705 eyes (1,680 normal and 1,025 VAE) to develop a predictive model (AI Tribute) following the KDD knowledge discovery framework, whose performance was assessed in two clinical scenarios – Normal versus Clinical Ectasia (KC+VAE-E) (N=3,335) and Normal versus VAE-NT (N=2,231) – by AUC and the DeLong test.

Purpose: To describe and evaluate a pilot technique using a sterile bandage contact lens (CL) as a spacer to overcome the minimum-depth limitations of applanation-based femtosecond laser (FSL) platforms when harvesting thin donor Bowman layer (BL) grafts, with preliminary clinical application in BL transplantation for advanced keratoconus (KC). Methods: This experimental and interventional case series included 9 in vitro donor corneas and 4 in vivo eyes with progressive KC. A ∼70-μm plano CL was applied to the bare donor stroma. The FSL dissection depth was programmed by adding the intended graft thickness to the CL thickness (110 μm for a ∼40-μm BL graft). Graft thickness and morphology were evaluated via optical coherence tomography (OCT). For the clinical cases, grafts were implanted into FSL-created stromal pockets; in vivo outcomes were limited to anterior segment OCT assessment of graft integration, graft thickness, and central corneal thickness over 12 months of follow-up. Results: The combined success rate for graft preparation was 92.3% (12/13). In vitro BL grafts yielded a median central thickness of 70 μm. The in vivo BL grafts achieved a median central thickness of 46 μm, with a median deviation of 1.5 μm from the individualized targets. Over the 12-month follow-up, anterior segment OCT showed all grafts to remain well integrated within the stromal pocket, with no displacement or interface complications. Conclusions: In this pilot study, the CL-assisted FSL protocol proved a reproducible method for harvesting BL grafts. By bypassing the minimum depth constraints of widely used applanation-based FSL platforms, this technique may minimize tissue loss and expand surgical access to BL transplantation for managing advanced KC, pending confirmation in larger series.

Ocular biomechanics may contribute to the variability of structural and functional outcomes in highly myopic eyes, but their role in myopic maculopathy remains unclear. This retrospective cohort study investigated whether in vivo corneal biomechanical parameters are associated with macular structural phenotypes and longitudinal functional changes. Fifty-four eyes with high myopia (≤−6 D; mean SE −15.6 ± 6.6 D) were evaluated at baseline and after 5.0 ± 0.1 years. Biomechanics were assessed with Corvis Scheimpflug Technology^®, macular structure was assessed with SD-OCT (6 × 6 mm), and function was assessed with Microperimeter MP-3 (CPS, dB). Foveoschisis was associated with higher A2 deformation amplitude (0.371 vs. 0.333 mm, p = 0.014) and SSI (0.986 vs. 0.827, p = 0.035). Staphyloma showed changes in the highest concavity radius (7.13 vs. 6.17 mm, p = 0.002), A1 deformation amplitude (0.150 vs. 0.132 mm, p = 0.001), and maximum deflection amplitude (1.03 vs. 1.19 mm, p = 0.013). Softer corneal parameters correlated with less functional loss, while stiffer parameters correlated with greater decline; similar trends were observed for fixation stability. These findings suggest that biomechanical profiles may vary across macular phenotypes and could be associated with functional evolution in highly myopic eyes.

Background/Objectives: To describe the progression of axial and segmental ocular biometric lengths and refractive status in adolescents and study independent associations between these changes and baseline ocular biomechanics. Methods: Prospective cohort of 126 eyes from 63 individuals followed for 2.5 years. Data from general health and lifestyle were collected through a validated questionnaire. Data from ocular biometry (IOL MASTER 700^®), objective refraction, and ocular biomechanics (Corvis ST^®) were collected at baseline and the end of follow-up timepoints. Biomechanical parameters were correlated with the variation in axial length (d_AL), vitreous cavity length (d_VCL), and spherical equivalent (d_SE). Multivariable linear regression models (one eye randomly assigned) adjusted for age, SE, and AL were developed to identify independent associations between baseline biomechanics and d_AL, d_VCL, and d_SE. Results: The cohort of the present work had a mean age of 14.1 ± 2.6 years at baseline. Variations of 0.122 ± 0.17 mm, 0.092 ± 0.17 mm, and −0.32 ± 0.9 D were found in AL, VCL, and SE at follow-up, respectively. Within the multivariable regression models, the biomechanical parameters found to be independently associated with d_AL (model 1), d_VCL (model 2), and d_SE (model 3) were as follows: Model 1—Biomechanically corrected IOP (bIOP), Integrated Radius (IR), and A2 Deflection Area (A2DArea); Model 2—bIOP, IR, and A2DArea; and Model 3—IR and WholeEyeMovementMAxTime (MaxWEMT). Conclusions: The study of ocular biomechanical behavior may play a pivotal role in the risk assessment of ocular elongation and myopic progression. This work found independent associations between ocular biomechanical behavior at baseline and axial and segmental ocular elongation and refractive myopization, mainly including bIOP, IR, and MaxWEMT.

The relationship between lifestyle, ocular biomechanical behavior, and myopia is not well established in the literature. The present study aims to describe changes in ocular biomechanics during adolescence and to explore their relationship with lifestyle factors and myopic progression. Prospective cohort study including 63 adolescents (126 eyes) with a mean age of 14.1 ± 2.6 years old examined twice over a 30 ± 0.9-month period. The data from biomechanics, biometry, corneal tomography, and lifestyle was addressed. The relationships between biomechanical changes, biometric and refractive variation, and lifestyle variables were analyzed using parametric and non-parametric statistics with a significance level of p < 0.05. A biomechanical stiffening trend was found. Axial elongation was 0.12 ± 0.17 mm, and refractive shift was −0.32 ± 0.87 D. The history of allergies was associated with greater axial growth (p = 0.032) and smaller increase in stress–strain-index (SSI) (p = 0.01). Myopization was higher in eyes with ocular surface symptoms (p = 0.049) and those with reported eye-rubbing habits (p = 0.04), with a lower gain in stiffness (p < 0.05). Outdoor activities were associated with higher gain in corneo-scleral stiffness (p < 0.05). Reduced myopization correlated directly with the increase in the SSI (p < 0.05) and inversely with the Integrated Radius (p < 0.05). Greater increases in axial length (AL), vitreous cavity length (VCL), and the ratio between VCL and AL (R_VCL/AL) correlated negatively with the increase in the SSI (p < 0.05). The increase in the R_VCL/AL correlated positively with the time spent on digital devices and negatively with the amount of outdoor activity (p < 0.05). Biomechanics may represent the physiological bridge between the environmental exposure and myopization, as lower gain in corneo-scleral stiffness was consistently associated with greater axial elongation and refractive myopization, with outdoor activity appearing to be protective.

Introduction This study aimed to assess the tomographic and biomechanical progression of non-operated eyes in patients with asymmetric keratoconus who underwent unilateral intracorneal ring segment (ICRS) implantation. Methods This retrospective study included 33 patients (66 eyes) with asymmetric keratoconus who underwent unilateral ICRS implantation. The fellow eye did not meet clinical or tomographic criteria for surgical intervention at the time of the initial surgery. Tomographic and biomechanical data from the non-operated fellow eye were compared between baseline and the final follow-up (minimum 12 months). Scheimpflug-based corneal tomography (Pentacam^®) assessed keratometry, curvature, corneal irregularity indices, and thickness-based metrics. Biomechanics parameters were evaluated via dynamic corneal response analysis (Corvis ST^®). Disease progression was defined as the presence of at least two concordant changes among the following: Kmax increase > 1.0 D, thinnest corneal thickness decrease > 20 µm, BAD-D increase > 0.42, and worsening of biomechanical E-stage. Results Over a median follow-up of 31 months, non-operated fellow eyes showed no clinically meaningful changes in visual, tomographic, or biomechanical parameters, suggesting no structural progression under conservative, behavior-based management, including counseling to avoid eye rubbing, management of atopic disease, and oral riboflavin supplementation. Disease progression was observed in only two eyes (6.1%), which were subsequently referred for corneal cross-linking (CXL). ICRS-treated eyes demonstrated significant improvements in visual acuity and corneal regularity. Conclusion In this paired-eye study, most non-operated fellow eyes in asymmetric keratoconus remained stable under conservative, behavior-based management combined with regular multimodal monitoring. These results support a behavior-first approach, using corneal tomography and biomechanics to detect objective progression and guide timely intervention. Conservative management in asymmetric keratoconus should be understood as an active, follow-up-dependent strategy rather than the absence of treatment. Surgical interventions should remain reserved for objectively progressing cases, recognizing that a small but clinically relevant proportion of fellow eyes still progress and require CXL.