Three-Year Corneal Biomechanical Outcomes Assessed by CORVIS ST Dynamic Scheimpflug Imaging After Epithelium-Off...

Area of Science:

• Ophthalmology
• Corneal Surgery
• Biomechanical Engineering

Background:

• Progressive keratoconus requires effective treatment to prevent vision loss.
• Corneal collagen cross-linking (CXL) is a standard treatment, with conventional and accelerated protocols available.
• Understanding long-term biomechanical and tomographic changes is crucial for treatment optimization.

Purpose of the Study:

• To compare the long-term (36-month) corneal biomechanical and tomographic outcomes of epithelium-off conventional CXL (C-CXL) versus accelerated CXL (A-CXL) in progressive keratoconus patients.
• To analyze dynamic corneal response parameters using Scheimpflug imaging.
• To evaluate the influence of irradiation duration on corneal stiffening.

Main Methods:

• Prospective comparative study of 63 eyes from 40 patients with progressive keratoconus.
• Epithelium-off CXL performed using either conventional (3 mW/cm² for 30 min) or accelerated (9 mW/cm² for 10 min) protocols, both delivering 5.4 J/cm² total fluence.
• Corneal parameters including Kmax, visual acuity, pachymetry, and dynamic Scheimpflug (Corvis ST) parameters (DA, A1T, A2T, PD, HC radius, SP-A1, BAD-D) assessed at baseline and 6, 12, 24, and 36 months.
• Statistical analysis included Welch's t-test and repeated-measures modeling.

Main Results:

• Both C-CXL and A-CXL demonstrated significant longitudinal biomechanical remodeling and clinical stabilization over 36 months (p < 0.001 for key parameters).
• No statistically significant between-group differences were observed at 36 months for Kmax, visual acuity, pachymetry, or most dynamic corneal response parameters (p > 0.05).
• A significant time × group interaction was found for the stiffness parameter at first applanation (SP-A1) (p=0.042), indicating a modest protocol-dependent divergence in stiffness trajectory over time.

Conclusions:

• Both epithelium-off conventional and accelerated CXL provide sustained biomechanical remodeling and clinical stabilization for progressive keratoconus over three years.
• While overall 36-month outcomes were comparable, the study highlights that matched total fluence does not guarantee identical biomechanical time courses.
• Irradiation duration appears to influence the pattern and trajectory of postoperative corneal stiffening, even when total energy is consistent.