Corneal OCT speckle differences in crosslinked and untreated rabbit eyes in response to elevated intraocular pressure

Abstract

Purpose : To investigate the impact of intraocular pressure (IOP) on corneal Optical Coherence Tomography (OCT) speckle in untreated and riboflavin–ultraviolet-A-induced collagen crosslinking rabbit eyes.

Methods : Eight New Zealand white rabbits aged 6 months at the study onset were used. The corneas of the left eyes were deepithelialized and crosslinked by application of riboflavin and 30-minute UVA light exposure (370nm, 3mW/cm²). The right untreated fellow eyes were used as controls. Six months after treatment, the animals were humanely euthanized. After enucleation, the whole eye globes were mounted in a special holder, where a G19 needle, connected to a pressure transducer and a syringe pump, was inserted into the anterior chamber. IOP was artificially increased from 15 to 45 mmHg in steps of 5 mmHg. At each IOP level, central cornea was imaged three times with spectral-domain OCT Copernicus HR (OPTOPOL, Poland) and a region of interest was automatically extracted (see Fig-A). The statistics of speckle signals were investigated by fitting the generalized gamma distribution to the signal envelope intensities. The scale (a) and shape (v, p) parameters were used for statistical analysis. Two-way repeated measures ANOVA was used to compare the effects of the IOP and treatment on the corneal speckle signal.

Results : The scale and both shape parameters of the fitted distribution in the untreated and crosslinked eyes were found to significantly change with increasing IOP (all P<0.001). The difference between untreated and crosslinked eyes was observed for the shape parameters (P=0.007 and P=0.002, for v and p, respectively). However, only the shape parameter (v) showed statistically significant interactions between the IOP and treatment (P=0.004).

Conclusions : Corneal OCT speckle statistics distinguished untreated rabbit corneas from those after crosslinking and showed that both corneas react, in terms of changes in their microstructure, to IOP increase. Analysis of the OCT speckle has the potential to provide, in an indirect and noninvasive way, information on the corneal microstructure.

This is a 2020 ARVO Annual Meeting abstract.

 

An example of a corneal OCT image with the region of interest delineated by the red lines (A); changes in the mean and standard errors of the scale (C) and shape (B, D) parameters of corneal OCT speckle in untreated (black) and crosslinked (red) rabbit eyes for different IOP values.