Relationship Among Corneal Stiffness, Thickness, and Biomechanical Parameters Measured by Corvis ST, Pentacam and ORA in Keratoconus.

Yu Zhao,Jing Zhao,Mi Tian,Yang Shen,Zhipeng Yan,Xingtao Zhou

doi:10.3389/fphys.2019.00740

Abstract

PurposeTo assess the relationship among corneal stiffness, thickness, and biomechanical parameters in keratoconus.SettingThe EENT Hospital of Fudan University, Shanghai, China.DesignComparative study.MethodsIn this cross-sectional prospective study, 75 keratoconic eyes of 44 patients were recruited. Eyes were divided three groups according to the steepest K-readings (Kmax): mild (31 eyes; 42.1–54.5D); moderate (27 eyes, 55.0–61.6D); and severe (17 eyes, 65.2–94.5D). Thirty-one healthy subjects were recruited as the control group. All patients underwent Corvis ST, Pentacam and ORA examinations at the same time. Stiffness parameter A1 (SP-A1) and other dynamic parameters were assessed using the Corvis ST. Kmax and thinnest corneal thickness (TCT) was obtained using the Pentacam. Corneal resistance factor (CRF) and corneal hysteresis (CH) were measured using the ORA. Analysis of correlation was applied to investigate the association between variables.ResultsThere was a decrease in SP-A1 in different stages of keratoconus compared with controls (P ≤ 0.001): with increasing severity, the value of SP-A1 became smaller (P < 0.05). A statistically significant linear relationship was noted between SP-A1 and TCT in each subgroup of keratoconus (P ≤ 0.001). In all three groups, SP-A1 was found to be positively correlated with first applanation time (P < 0.01), while negatively correlated with deformation amplitude (P < 0.05). Analysis of SP-A1 with regard to CRF and CH indicated statistically positive correlation in keratoconus (P < 0.05).ConclusionSignificant decreases in corneal stiffness were noted in kerotoconic eyes compared with normal eyes. The stiffness parameter could be a valuable clinical tool enables biomechanically track progression with keratoconus.SynopsisOur study found that corneal thinning and biomechanical decreasing synchronize with one another throughout the progression of the keratoconus, and SP-A1 could be a potential biomarker evaluating disease progression.

Highlights

Keratoconus is a progressive, non-inflammatory disease in which the cornea forms a conical shape, and thins due to significant structural degeneration
Studies have shown that corneal hysteresis (CH) and corneal resistance factor (CRF) in kerotoconic eyes are significantly lower than in normal eyes, the specificity and sensitivity of both values are not sufficiently high to diagnosis keratoconus (Shah et al, 2007; Fontes et al, 2011)
We explored the relationship among corneal stiffness, corneal thickness, and biomechanical parameters in different stages of keratoconus assessed using the Corvis ST and the Ocular Response Analyzer (ORA)

Summary

Introduction

Keratoconus is a progressive, non-inflammatory disease in which the cornea forms a conical shape, and thins due to significant structural degeneration. It results in corneal protrusion, irregular astigmatism, and loss of visual acuity (Krachmer et al, 1984; Lawless et al, 1989). The ex vivo measurement destroys the natural state of the cornea, and is likely to be influenced by multiple factors (Elsheikh and Anderson, 2005). The Ocular Response Analyzer (ORA; Reichert Inc, Depew, NY, United States) was introduced as the first device for evaluating corneal biomechanical parameters in vivo. It monitors the corneal deformation response to an air pulse, and provides biomechanics-related parameters including corneal hysteresis (CH) and corneal resistance factor (CRF). Studies have shown that CH and CRF in kerotoconic eyes are significantly lower than in normal eyes, the specificity and sensitivity of both values are not sufficiently high to diagnosis keratoconus (Shah et al, 2007; Fontes et al, 2011)

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