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Correlation of the Corvis Biomechanical Factor with tomographic parameters in keratoconus
Elias Flockerzi1, Riccardo Vinciguerra, Michael Wellington Belin
1From the Department of Ophthalmology, Saarland University Medical Center, Homburg, Germany (Flockerzi, Seitz); Humanitas San Pio X Hospital, Milan, Italy (Vinciguerra); School of Engineering, University of Liverpool, Liverpool, United Kingdom (Vinciguerra); Department of Ophthalmology & Vision Science, University of Arizona, Tucson, Arizona (Belin); Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Milan, Italy (Vinciguerra); Humanitas Clinical and Research Center, IRCCS, Rozzano (Mi), Italy (Vinciguerra); Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro, Brazil (Ambrósio).
Purpose:
To investigate the relationship between corneal biomechanics and keratoconus (KC) severity as described by tomographic parameters.
Setting:
University-based German ophthalmology department.
Design:
Retrospective cross-sectional study.
Methods:
A total of 448 KC corneas of the Homburg Keratoconus Center and 112 healthy corneas (448+112 patients) were examined by Pentacam high-resolution and Corneal Visualization Scheimpflug Technology (Pentacam HR and Corvis ST). The KC population included a wide spectrum of disease severity based on Belin's ABCD classification. Linear regression analysis was performed between the linear term of the Corvis Biomechanical Index (CBI) (CBI beta) and the tomographic values anterior radius of curvature (ARC), posterior radius of curvature (PRC), and thinnest corneal thickness (TCT). A linear transformation of the CBI beta was performed to provide an intuitive scaling, which was referred to as the Corvis Biomechanical Factor (CBiF = -0.24294226 × CBI beta + 6.02). This scaling adjusted the CBI beta to the same scale as posterior corneal curvature (PRC).
Results:
There was a high correlation of the CBI beta and its modification, the CBiF, with TCT (Pearson, r = -0.775), ARC (r = -0.835), and PRC (r = -0.839) in the KC population (P < .001). In the control corneas, the correlation between the CBI beta and ARC was weak (r = -0.216, P = .022), not significant (PRC, r = -0.146, P = .125), or moderate (TCT, r = -0.628, P < .001).
Conclusions:
The linear term of the CBI was highly associated with KC severity as defined by corneal tomography. The CBiF represents a new scale based on biomechanical characteristics in KC, which could serve as a basis for a biomechanical KC classification in the future.
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