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Linking layered corneal compactness to macroscopic biomechanics: in vivo assessment via integrated densitometry and
Fuqi Deng1,2,3, Huazheng Cao4, Wenjing Gao1,2,3,5
1Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China.
Objective:
To investigate in vivo correlations between corneal dynamic deformation properties and structural compactness via layered densitometry, clarifying the main contributions of the corneal anatomical layers to macroscopic biomechanics.
Design:
Cross-sectional study.
Methods:
In the study, a total of 221 eyes from 221 healthy participants were enrolled. Corneal deformation properties were measured by the air-puff Corvis ST. Scheimpflug images of the cornea were captured to examine 50-sublayer densitometry values using the caliper technique. According to the spatial patterns of corneal densitometry with depth, the whole cornea was then divided into multiple layers. Different layers were corresponding to different corneal structures (epithelium, Bowman membrane, anterior, middle, and posterior stroma, Descemet membrane, and, endothelium). In each layer, 19 predetermined data point (1, 6, 12 points on the central, paracentral, and peripheral zones, respectively) were taken out for analysis.
Results:
Layered densitometry analysis revealed distinct structural compactness patterns across seven corneal layers (epithelium to endothelium). Significant correlations emerged between densitometry values and dynamic biomechanical parameters, exhibiting strong layer-specific and regional dependencies. The anterior cornea (Bowman's membrane and anterior stroma) showed the most robust associations: increased densitometry in these layers correlated positively with stiffness parameters (SPA1 [stiffness parameter in the first applanation], SPHC [stiffness parameter highest concavity]; central SPHC r = 0.3, P < 0.001) and negatively with deformation susceptibility metrics (DeflAmpMax [maximum deflection near highest concavity], IR [Integrated radius]; central IR r = -0.229, P < 0.001). These correlations weakened posteriorly and peripherally. Mid-stromal and posterior layers demonstrated a weak biomechanical relevance, while Descemet's membrane and endothelium exhibited isolated regional associations.
Conclusion:
The study established the in vivo evidence linking layer-specific corneal compactness (densitometry) to macroscopic biomechanics, with anterior stromal compactness being the primary determinant of corneal stiffness parameter. Higher densitometry in anterior layers was associated with a stiffer corneal response, such as a higher SPA1 and a lower overall deformation amplitude. Descemet's membrane's densitometry-reflected structural state minimally modulates whole-corneal deformation. This densitometry-deformation framework may help elucidate microstructural alterations underlying corneal disease, surgery and biomechanical dysfunction, transcending conventional whole-cornea biomechanical assessments.
