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.

The aim of this study was to evaluate the influence of increase in intraocular pressure (IOP) and cooccurring changes in ocular biometry parameters on the corneal optical coherence tomography (OCT) speckle distribution in ex-vivo experiments on porcine intact eyes. Twenty-three eyeballs were used in the inflation test where IOP in the anterior chamber was precisely set from 10 mmHg to 40 mmHg in steps of 5 mmHg and where eye biometry was utilized (IOL Master 700). To assess the influence of the duration of the experiment on the OCT speckle statistics, the second experiment was performed with 10 eyeballs at the constant IOP of 15 mmHg. Based on the OCT scans of central cornea (Copernicus REVO), spatial maps of the scale parameter (a) and the shape parameter (v) of the gamma distribution speckle model were estimated. The means of both parameters for each spatial map were computed within the 2 mm of the central stroma. Both distributional parameters statistically significantly varied with IOP and time (one way repeated measures ANOVA, all p-values < 0.001). The a parameter revealed a faster statistically significant increase in IOP up to 25 mmHg, regardless of time. Central corneal thickness (CCT), the anterior chamber depth, and the mean equivalent spherical power varied significantly with IOP, whereas CCT and axial length changed statistically significantly with time. Statistically significant correlation was found between CCT and the a parameter, after removing IOP as a confounding factor (r = −0.576, p < 0.001). The parameters of the gamma distribution can be used not only for identifying IOP induced changes in the optical scattering within the corneal stroma, but also in corneal geometry. The approach of corneal speckle analysis could be potentially utilized for an indirect and noninvasive assessment of some properties of corneal stroma.

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