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CORNEAL BIOMECHANICS AND THEIR CLINICAL IMPORTANCE IN
KERATOCONUS
Jalalova Dilfuza Zuhridinovna
Scientific supervisor.
Department of Ophthalmology, Samarkand State Medical University
Yaxshinorov Islombek
Samarkand State Medical University, Department of Ophthalmology, 2
st year clinical ordinator.
https://doi.org/10.5281/zenodo.17583857
Annotation.
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
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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 regression in 85% of treated eyes. The improvement in
biomechanical parameters correlated with reduced progression rates and enhanced best-corrected
visual acuity. These findings confirm the critical role of biomechanical assessment in evaluating
disease activity and treatment response.
Discussion
The study highlights the clinical significance of corneal biomechanics in
understanding, diagnosing, and managing keratoconus. Biomechanical degradation precedes
morphological alterations, making parameters like corneal hysteresis and corneal resistance factor
reliable early markers. The correlation between biomechanical weakening and disease severity
underscores the importance of incorporating these measurements into standard diagnostic
protocols. Tools such as ORA and Corvis ST have expanded clinical capabilities by quantifying
the cornea’s viscoelastic response to stress. Early detection of biomechanical instability enables
prompt initiation of corneal cross-linking, which effectively halts progression by increasing
collagen cross-link density and restoring corneal stiffness. Post-CXL improvement in
biomechanical parameters, as demonstrated in this study, validates its long-term efficacy in
stabilizing the cornea. Additionally, understanding biomechanical variability assists in
customizing surgical interventions, including intracorneal ring segment implantation and
refractive surgery, minimizing the risk of postoperative ectasia. The integration of biomechanical
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data with topographic and tomographic indices creates a comprehensive framework for risk
stratification, enabling clinicians to distinguish between stable and progressive keratoconus. This
multidisciplinary approach advances precision medicine in ophthalmology and enhances patient
outcomes through evidence-based, individualized care.
Conclusion
Corneal biomechanics play a fundamental role in the pathophysiology and
management of keratoconus. Parameters such as corneal hysteresis, corneal resistance factor, and
deformation amplitude provide valuable information on corneal integrity and serve as early
diagnostic markers. The incorporation of biomechanical assessment tools enhances diagnostic
accuracy, facilitates timely therapeutic intervention, and guides personalized treatment strategies.
Corneal cross-linking remains the cornerstone therapy for biomechanical reinforcement,
effectively stabilizing disease progression. Continuous advancements in imaging and
biomechanical modeling will further refine our ability to predict keratoconus behavior and
optimize treatment outcomes. Routine biomechanical evaluation should be integrated into clinical
practice for early detection, progression monitoring, and postoperative assessment, ultimately
improving visual prognosis and reducing the burden of corneal transplantation.
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