Purpose: To compare corneal biomechanical parameters in eyes with keratoconus and post-refractive surgery ectasia using Scheimpflug-based imaging and to evaluate whether distinct biomechanical signatures can aid in differentiating the two entities. Methods: This observational cross-sectional study included 80 eyes of 60 subjects — 40 with keratoconus (Group A) and 40 with post-refractive surgery ectasia (Group B). All participants underwent corneal assessment with Pentacam HR and Corvis ST. Parameters such as stiffness parameter (SP-A1), deformation amplitude (DA ratio), integrated radius, and Ambrosio Relational Thickness (ARTmax) were compared between groups. Data were analyzed using independent t-test, with p < 0.05 considered statistically significant. Results: Mean SP-A1 was significantly lower in post-refractive ectasia (67.8 ± 12.5) compared to keratoconus (75.6 ± 14.2, p = 0.01), indicating greater biomechanical weakness post-surgery. DA ratio and integrated radius were both higher in ectasia (1.12 ± 0.04 and 8.23 ± 0.6 respectively) than in keratoconus (1.05 ± 0.03 and 7.68 ± 0.5; p < 0.01). ARTmax was significantly reduced in both groups but lowest in post-refractive ectasia (230.4 ± 35.2 µm vs 258.7 ± 32.5 µm). Conclusion: Scheimpflug-based biomechanical assessment demonstrates quantifiable differences between keratoconus and post-refractive ectasia. Post-refractive ectasia shows greater structural destabilization and lower corneal stiffness, suggesting different pathophysiological mechanisms despite overlapping topographic features.
Keratoconus (KC) and post-refractive surgery ectasia (PRE) represent progressive corneal thinning disorders that compromise visual quality and structural integrity [1,2]. Although they share similar topographic patterns — inferior steepening, posterior elevation, and reduction in corneal thickness — their underlying pathophysiology differs [3]. Keratoconus is a naturally occurring, bilateral, asymmetric, non-inflammatory ectasia, while PRE follows iatrogenic biomechanical weakening of the cornea [4]. Recent advancements in Scheimpflug-based imaging (e.g., Pentacam HR and Corvis ST) allow simultaneous quantification of corneal biomechanics, providing insight into tissue stiffness, viscoelasticity, and deformation dynamics under air puff stress [5].
This cross-sectional study was conducted between January 2024 and September 2024 at a tertiary eye care centre. The study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Ethics Committee.
Group A: 40 eyes diagnosed with keratoconus based on Belin–Ambrosio Enhanced Ectasia Display.
Group B: 40 eyes with clinically diagnosed post-LASIK or post-PRK ectasia.
Exclusion criteria included prior corneal cross-linking, active ocular surface disease, corneal scarring, trauma, or systemic connective tissue disorder [6].
Each participant underwent Pentacam HR (Oculus, Germany) and Corvis ST imaging. Parameters assessed included DA Ratio, Integrated Radius, SP-A1, and ARTmax. Only scans with a quality index ≥95% were included [7].
|
Parameter |
Keratoconus (Mean ± SD) |
Post-Refractive Ectasia (Mean ± SD) |
p-value |
|
SP-A1 (mmHg/mm) |
75.6 ± 14.2 |
67.8 ± 12.5 |
0.01 |
|
DA Ratio |
1.05 ± 0.03 |
1.12 ± 0.04 |
<0.001 |
|
Integrated Radius (mm) |
7.68 ± 0.5 |
8.23 ± 0.6 |
0.004 |
|
ARTmax (µm) |
258.7 ± 32.5 |
230.4 ± 35.2 |
0.002 |
Both groups exhibited reduced stiffness compared to normal reference values, but biomechanical degradation was more pronounced in post-refractive ectasia. A moderate positive correlation was observed between CCT and SP-A1 (r = 0.61, p < 0.001) [8].
Our findings highlight the distinct biomechanical profiles of keratoconus and post-refractive ectasia. Although both exhibit thinning and reduced stiffness, post-surgical ectasia showed significantly lower SP-A1 and higher DA ratio, suggesting more generalized biomechanical destabilization [9,10]. Similar observations were made by Vinciguerra et al. (2016) and Tomita et al. (2018), supporting the idea that surgical alteration of stromal structure induces abrupt redistribution of corneal stress [11,12]. Integrating biomechanical parameters with Scheimpflug tomography enhances diagnostic precision beyond curvature maps alone [13].
Scheimpflug-based corneal biomechanics offer an invaluable adjunct for differentiating keratoconus from post-refractive ectasia. Post-surgical ectatic corneas demonstrate significantly reduced stiffness and higher deformation responses [14]. Integrating biomechanical assessment with corneal tomography enhances diagnostic confidence and may help tailor individualized management strategies [15,16].
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