Structural, functional and blood perfusion changes in the rat retina associated with elevated intraocular pressure, measured simultaneously with a combined OCT+ERG system.

Bingyao Tan,Erik Mason,Benjamin Maclellan,Kostadinka Bizheva,Demetrios G Vavvas

doi:10.1371/journal.pone.0193592

Abstract

Acute elevation of intraocular pressure (IOP) to ischemic and non-ischemic levels can cause temporary or permanent changes in the retinal morphology, function and blood flow/blood perfusion. Previously, such changes in the retina were assessed separately with different methods in clinical studies and animal models. In this study, we used a combined OCT+ ERG system in combination with Doppler OCT and OCT angiography (OCTA) imaging protocols, in order to evaluate simultaneously and correlate changes in the retinal morphology, the retinal functional response to visual stimulation, and the retinal blood flow/blood perfusion, associated with IOP elevation to ischemic and non-ischemic levels in rats. Results from this study suggest that the inner retina responds faster to IOP elevation to levels greater than 30 mmHg with significant reduction of the total retinal blood flow (TRBF), decrease of the capillaries’ perfusion and reduction of the ON bipolar cells contribution to the ERG traces. Furthermore, this study showed that ischemic levels of IOP elevation cause an additional significant decrease in the ERG photoreceptor response in the posterior retina. Thirty minutes after IOP normalization, retinal morphology, blood flow and blood perfusion recovered to baseline values, while retinal function did not recover completely.

Highlights

Elevated intraocular pressure (IOP) is a well-known risk factor in open angle glaucoma (OAG) and it is the most studied pathogenic characteristic of OAG
Morphological data from our study showed deformation of the optic nerve head (ONH) with elevated IOP, which increased progressively in magnitude with increase of the IOP level
Similar ONH morphological change with elevated IOP was observed in a number of studies that utilized different IOP elevation methods, including the vascular loop technique, as well as different IOP levels [25,37,38]

Summary

Introduction

Elevated intraocular pressure (IOP) is a well-known risk factor in open angle glaucoma (OAG) and it is the most studied pathogenic characteristic of OAG. Only a few studies have reported assessment of both retinal blood flow and function during IOP manipulation[12,13,14,15] In all of those studies, either separate groups of animals were used, or ocular blood flow (combined retinal and choroidal flow) was measured invasively by a laser Doppler flowmetry probe. A combined OCT and ERG system would enable simultaneous, non-invasive imaging and assessment of retinal morphology, blood flow and function, which would reduce the variance in the acquired data. Such a combined OCT+ERG system has been used recently to assess simultaneously and correlate visually evoked intrinsic optical signals with ERG recordings and with retinal morphology in chicken[16,17]. The OCT+ERG technology combined with various scanning protocols for Doppler OCT and OCT angiography (OCTA) could serve as a very useful research tool to investigate the dynamic relationship between morphological, blood flow and functional changes in the retina for various retinal diseases

Methods

Results

Conclusion