SIGNIFICANCE Optical coherence tomography speckle is used here in an unconventional way as the indirect source of information on tissue microstructure. The study reveals that the corneal speckle of glaucoma suspects has a similar relationship between the parameters of scattering exhibited in glaucoma patients. PURPOSE The purpose of this study was to evaluate the potential of optical coherence tomography imaging of the cornea in early diagnosis of glaucoma. METHODS Corneas of 64 subjects of three groups, including 18 primary open-angle glaucoma patients, 24 glaucoma suspects with normal levels of IOP and uncompromised visual field, and 22 age-matched controls, were imaged with spectral optical coherence tomography. A central region of interest in each optical coherence tomography image visualizing the stroma was automatically extracted, and the intensity data within that region were fit with the generalized gamma distribution. Its parameters describe the scatterer cross section and scatterer density and indirectly assess corneal microstructure. In addition, subjects underwent measurements of IOP, visual field, Heidelberg Retinal Tomography, retinal nerve fiber layer thickness, and biometry. Group means of all parameters were tested for equality. Within each group of subjects, correlation was evaluated between the statistical parameters of the corneal speckle. RESULTS Glaucoma suspects had statistically significantly different IOP, visual field parameters, mean retinal fiber layer thickness, and central corneal thickness from those of glaucoma patients but not from those of the control group. The parameters of the corneal speckle were not significantly different between the groups, but they showed a markedly higher and statistically significant coefficient of determination for glaucoma patients and suspects than that for the control group (0.927 and 0.707 vs. 0.336). CONCLUSIONS The results indicate that glaucoma suspects have similar relationship between the corneal scatterer cross section and scatterer density to that exhibited in the glaucoma patients but markedly different from that of healthy controls.

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.