Assessment of Keratoconus Risk in Very Asymmetric Ectasia Using Corneal Tomographic and Biomechanical Parameters

Xiaoyu Zhang,1– 3,* Lan Ding,1– 3,* Ling Sun,1– 3 Bingqing Sun,1– 3 Yangyi Huang,1– 3 Yishan Qian,1– 3,* Xingtao Zhou1– 3,* 1Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, People’s Republic of China; 2Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, People’s Republic of China; 3Shanghai Research Center of Ophthalmology and Optometry, Eye & ENT Hospital, Fudan University, Shanghai, 200031, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yishan Qian; Xingtao Zhou, Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, People’s Republic of China, Tel +86-21-64377134, Fax +86-21-64377151, Email thronebird31@hotmail.com; doctzhouxingtao@163.comPurpose: To investigate the relationship between corneal tomographic or biomechanical parameters and risk of keratoconus in very asymmetric ectasia (VAE).Methods: This retrospective case-control single-centre study included patients with VAE and normal controls. The VAE group had clinical ectasia in one eye and normal topography (VAE-NT) in the fellow eye; VAE-NT eyes were selected for analysis. The control group was selected from corneal refractive surgery candidates; the right eye was enrolled. Scheimpflug-based corneal tomography (Pentacam) and corneal biomechanical assessment (Corvis ST) were performed. Univariate and multivariable logistic regression were performed using Cox proportional hazards models to evaluate keratoconus-associated risk factors. A two-piecewise linear regression model was applied to examine the threshold effect of selected vital paragmeters on the risk of keratoconus according to a smoothing plot.Results: Threshold effect between tomographic integration and risk of keratoconus was observed. Discrepancy between the central corneal thickness and thinnest corneal thickness (discrepancy CCT vs TCT) greater than 5 μm, discrepancy between the apex corneal thickness and thinnest corneal thickness (discrepancy ACT vs TCT) greater than 3 μm, vector distance between CCT and TCT (distance CCT vs TCT) greater than 0.65 mm indicated a significant increased risk of keratoconus. Risk of keratoconus decreased when distance CCT vs TCT was less than 0.65 mm.Conclusion: Discrepancy CCT vs TCT, discrepancy ACT vs TCT, and distance CCT vs TCT can be used as indicators for risk assessment of early keratoconus.Keywords: keratoconus, corneal tomographic, corneal biomechanical, very asymmetric ectasia