Influence of eye biometrics and corneal micro-structure on noncontact tonometry.

Danilo A Jesus,Patrycja Krzyżanowska-Berkowska,D Robert Iskander,Małgorzata Majewska,Sanjoy Bhattacharya

doi:10.1371/journal.pone.0177180

Danilo A Jesus, Patrycja Krzyżanowska-Berkowska + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0177180

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Abstract

PurposeTonometry is widely used as the main screening tool supporting glaucoma diagnosis. Still, its accuracy could be improved if full knowledge about the variation of the corneal biomechanical properties was available. In this study, Optical Coherence Tomography (OCT) speckle statistics are used to infer the organisation of the corneal micro-structure and hence, to analyse its influence on intraocular pressure (IOP) measurements.MethodsFifty-six subjects were recruited for this prospective study. Macro and micro-structural corneal parameters as well as subject age were considered. Macro-structural analysis included the parameters that are associated with the ocular anatomy, such as central corneal thickness (CCT), corneal radius, axial length, anterior chamber depth and white-to-white corneal diameter. Micro-structural parameters which included OCT speckle statistics were related to the internal organisation of the corneal tissue and its physiological changes during lifetime. The corneal speckle obtained from OCT was modelled with the Generalised Gamma (GG) distribution that is characterised with a scale parameter and two shape parameters.ResultsIn macro-structure analysis, only CCT showed a statistically significant correlation with IOP (R2 = 0.25, p<0.001). The scale parameter and the ratio of the shape parameters of GG distribution showed statistically significant correlation with IOP (R2 = 0.19, p<0.001 and R2 = 0.17, p<0.001, respectively). For the studied group, a weak, although significant correlation was found between age and IOP (R2 = 0.053, p = 0.04). Forward stepwise regression showed that CCT and the scale parameter of the Generalised Gamma distribution can be combined in a regression model (R2 = 0.39, p<0.001) to study the role of the corneal structure on IOP.ConclusionsWe show, for the first time, that corneal micro-structure influences the IOP measurements obtained from noncontact tonometry. OCT speckle statistics can be employed to learn about the corneal micro-structure and hence, to further calibrate the IOP measurements.

Highlights

Glaucoma is the leading cause of global irreversible blindness [1]
Macro-structural analysis included the parameters that are associated with the ocular anatomy, such as central corneal thickness (CCT), corneal radius, axial length, anterior chamber depth and white-to-white corneal diameter
Forward stepwise regression showed that CCT and the scale parameter of the Generalised Gamma distribution can be combined in a regression model (R2 = 0.39, p

Summary

Introduction

Glaucoma is the leading cause of global irreversible blindness [1]. It affects more than 70 million people worldwide and it is estimated to reach 111.8 million in 2040 [2]. The accuracy of applanation tonometry is influenced by corneal stiffness that varies with a number of parameters, such as thickness, curvature and age [6]. Unlike CCT, the effect of CR is small and limited to a range between 0.57 mmHg/1mm to 1.14 mmHg/1mm [6] Both CCT and CR may be viewed as corneal macro-structural parameters that influence the accuracy of applanation tonometry. In vitro experiments [12,13] and theoretical models [14] have shown that the cornea exhibits mechanical and viscoelastic properties This may explain the wide range obtained for CCT correction and indicate that the macro-structure described by CCT and CR only partially explains the variance of IOP whereas other properties, related to the micro-structure of the cornea, may contribute [15]

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