We analyzed the relationship among 15 in vivo corneal biomechanical variables and AST in the nasal and temporal regions. Because CCT, IOP, and age are known to influence corneal deformation responses to air puffs, adjustments were made for these factors. The results revealed that SP-HC (r
NAST0 = 0.369, r
NAST1 = 0.236, r
NAST2 = 0.217, and r
TAST0 = 0.480) and A2V (r
NAST0 = 0.255, r
NAST1 = 0.217, and r
NAST2 = 0.241) were significantly and positively correlated with AST (
P < 0.05). SP-HC, introduced by Roberts et al.,
19 represents the SP-HC based on finite element modeling corrected for IOP. This parameter is defined as the ratio of load to displacement. Specifically, it uses Corvis ST's air-puff pressure on the cornea, measured by hot-wire anemometry, minus the biomechanically corrected IOP, then divided by the displacement between the first applanation and highest concavity.
19 In clinical practice, higher SP-HC values are associated with smaller displacements at the maximum concavity point, indicating stronger corneal biomechanical properties. Our findings suggest that higher SP-HC values may result from a thicker sclera near the limbus, where the elevated collagen fiber and matrix contents enhance biomechanical properties and restrict corneal deformation. Ex vivo experiments demonstrated significantly higher SP-HC values after stiffening human donor sclera with 4% glutaraldehyde,
12 which indirectly supports our findings. This relationship is likely attributed to the increased resistance of stiffer scleral tissue to aqueous humor displacement during maximum corneal deformation, thereby limiting the extent of deformation.
12,20,21 Previous numerical simulation studies have emphasized the role of the sclera and aqueous humor in limiting the corneal deformation response.
22–24 The inclusion or not of the sclera in the numerical simulation of the air puff test, or the simulation of a more or less compliant behavior, can significantly alter corneal biomechanical characterizations.
22–25 Moreover, Montanino et al.
26 demonstrated that the distribution of aqueous humor influences corneal displacement. Based on in silico models, our study confirms these findings from an in vivo perspective, further validating their reliability. Ma et al.
27 hypothesized that SP-HC could serve as an in vivo parameter for assessing scleral biomechanics, but this hypothesis lacked validation through in vivo experiments. Our results suggest that SP-HC partially reflects scleral biomechanical properties, providing further evidence for its clinical applicability. Given its strong correlation with scleral thickness and ex vivo biomechanics, SP-HC may be a valuable parameter for indirectly quantifying scleral biological and biomechanical properties, particularly in the absence of direct measurement tools in clinical practice. The strategy proposed in this research offers a quick and clinically feasible method to assist with characterizing in vivo scleral biomechanics. It is also worth noting that optical coherence elastography (OCE) is a promising technique for directly estimating scleral biomechanics.
28,29 OCE allows for localized biomechanical assessment and offers precise measurements, with potential for clinical application in the near future.