CORNEAL BIOMECHANICS AND THEIR CLINICAL IMPORTANCE IN KERATOCONUS

Аннотация

Keratoconus is a progressive ectatic disorder characterized by localized thinning and protrusion of the cornea, leading to irregular astigmatism and visual distortion. Recent advances in corneal biomechanics have revolutionized our understanding of its pathogenesis, progression, and treatment strategies. This study aims to evaluate the biomechanical parameters of the cornea—such as corneal hysteresis, corneal resistance factor, and elasticity modulus—and their diagnostic and prognostic significance in patients with keratoconus. By analyzing 150 patients using the Ocular Response Analyzer and Corvis ST, the research highlights early biomechanical changes preceding topographic abnormalities. The results underscore the clinical importance of biomechanical assessment in early detection, risk stratification, and personalized treatment planning, including collagen cross-linking and intracorneal ring segment implantation. Understanding corneal biomechanics provides a foundation for improving outcomes in keratoconus management and reducing the need for corneal transplantation. Keywords: corneal biomechanics, keratoconus, corneal hysteresis, corneal resistance factor, corneal cross-linking, topography, corneal elasticity. Introduction Keratoconus is a non-inflammatory, degenerative corneal disorder marked by progressive thinning and anterior protrusion of the cornea, resulting in irregular astigmatism, higher-order aberrations, and visual impairment. Although the exact etiology remains multifactorial—encompassing genetic, biochemical, and environmental factors—the biomechanical instability of the corneal stroma plays a pivotal role in disease progression. Traditional diagnostic tools such as corneal topography and tomography primarily detect structural changes, which often appear at relatively advanced stages. Recent technological advancements have enabled direct assessment of corneal biomechanics, offering valuable insights into the viscoelastic properties and deformation behavior of the corneal tissue. Corneal hysteresis (CH) and corneal resistance factor (CRF) have emerged as critical indicators of corneal integrity and elasticity. Lower CH and CRF values are consistently associated with keratoconus, even before topographic irregularities become evident. The biomechanical weakening of the cornea predisposes it to further deformation under intraocular pressure, perpetuating a cycle of progression. Therefore, integrating biomechanical evaluation into clinical practice enhances the precision of diagnosis, enables early detection of subclinical keratoconus, and guides therapeutic decision-making, particularly in candidates for refractive surgery. This study focuses on the 89 Noyabr, 2025-Yil correlation between biomechanical parameters and disease severity, highlighting the clinical relevance of these measurements in optimizing patient management. Materials and Methods The study included 150 participants aged 15–40 years, divided into two groups: 100 patients diagnosed with varying stages of keratoconus and 50 age-matched healthy controls. Diagnosis was confirmed through slit-lamp examination, corneal topography (Pentacam HR), and tomography. Biomechanical parameters, including corneal hysteresis and corneal resistance factor, were measured using the Ocular Response Analyzer (ORA; Reichert Technologies). Corneal deformation amplitude, integrated radius, and stiffness parameter at the first applanation were evaluated using the Corvis ST (Oculus Optikgeräte GmbH). Exclusion criteria included prior corneal surgery, ocular inflammation, and systemic connective tissue disorders. Statistical analysis was conducted using SPSS 25.0, with p<0.05 considered statistically significant. Pearson correlation coefficients were calculated to assess the relationship between biomechanical parameters and keratoconus severity. The study also analyzed pre- and post- treatment biomechanical outcomes in patients undergoing corneal collagen cross-linking (CXL). Follow-up assessments were performed at 1, 3, 6, and 12 months postoperatively to evaluate biomechanical strengthening and topographic stabilization. Results Patients with keratoconus demonstrated significantly lower mean corneal hysteresis (8.1 ± 1.4 mmHg) and corneal resistance factor (7.5 ± 1.2 mmHg) compared with controls (CH 10.9 ± 1.3 mmHg; CRF 10.4 ± 1.1 mmHg; p<0.001). Corneal deformation amplitude was markedly higher in keratoconus patients (1.19 ± 0.12 mm) versus controls (0.89 ± 0.08 mm; p<0.001), indicating reduced biomechanical rigidity. Stiffness parameter at first applanation (SP- A1) values were significantly decreased, confirming corneal softening. There was a strong negative correlation between corneal hysteresis and maximum keratometry (r = -0.62, p<0.01), reflecting biomechanical deterioration with disease progression. Following CXL, corneal hysteresis increased by 14% and CRF by 11% after 12 months, while topographic indices demonstrated stabilization or regressio