Correlation of optical coherence tomography with clinical and histopathological findings in experimental autoimmune uveoretinitis

https://doi.org/10.1016/j.exer.2011.04.012Get rights and content

Abstract

Optical coherence tomography (OCT) is becoming the state-of-the-art method for the non-invasive imaging of a variety of ocular diseases. The aim of this study was to assess the application of OCT for the in vivo monitoring and follow-up of pathological changes during experimental autoimmune uveoretinitis (EAU) in rats. Initially we established OCT imaging in healthy brown Norway rats and correlated it with retinal histology. Subsequently, we induced EAU and imaged animals by OCT throughout the pre-peak, peak, and post-peak phases of the disease. The sensitivity of OCT imaging was determined by comparison with clinical EAU and histopathology scores obtained ex vivo at several time points throughout the disease course. Our data demonstrate that OCT imaging of the healthy rat retina closely correlates with histological observations and allows the clear visualization of all retinal layers. After induction of EAU, the first pathological changes could be detected by OCT at day (d) 8 post-immunization (p.i.) which corresponded to the time point of clinical disease onset. An increase in retinal thickness (RT) was detected from d10 p.i. onwards which peaked at d16 p.i. and decreased again to near control levels by d20 p.i. We introduce a novel semi-quantitative OCT scoring which correlates with histopathological findings and complements the clinical scores. Therefore, we conclude that OCT is an easily accessible, non-invasive tool for detection and follow-up of histopathological changes during EAU in rats. Indeed, significant differences in RT between different stages of EAU suggest that this OCT parameter is a sensitive marker for distinguishing disease phases in vivo.

Highlights

► OCT is a state-of-the-art non-invasive imaging technique. ► We investigated the use of OCT to monitor EAU in rats. ► OCT imaging correlates with retinal histopathology in healthy animals and throughout EAU. ► With retinal thickness, OCT can be used to monitor the onset and progression of EAU. ► We propose a novel, semi-quantitative OCT scoring system.

Introduction

Experimental autoimmune uveoretinitis (EAU) is an animal model of autoimmune uveitis, a group of diseases which target the uvea and retina. The main features include retinal and choroidal inflammation, vasculitis, photoreceptor destruction, and ultimately, loss of vision (Caspi et al., 1996, Chan et al., 1990). EAU can be induced in various animal species by active immunization with different retinal antigens, such as retinal soluble antigen or interphotoreceptor retinoid-binding protein (IRBP) (Adamus and Chan, 2002), or by adoptive transfer of autoreactive T cells (Caspi et al., 1986, Caspi, 2003).

Longitudinal in vivo studies of the pathological changes during EAU are necessary for elucidation of the disease-causing mechanisms and for monitoring disease onset and progression during therapeutic intervention. In order to perform such examinations, non-invasive, accurate techniques, which allow for repetitive reproducible imaging, should be used. Recently, a number of studies have indicated that optical coherence tomography (OCT) is becoming the state-of-the-art imaging technique for performing high-resolution, cross-sectional ophthalmic imaging (Fujimoto et al., 2000, Li et al., 2001, Grieve et al., 2004, Srinivasan et al., 2006, Ruggeri et al., 2007, Sakata et al., 2009). OCT is especially useful in serial observations of disease development, because it can provide images of tissue in vivo and in real time, without the need for excision and processing of specimens (Fujimoto, 2003).

However, up to now, no studies have assessed the efficacy of OCT for monitoring EAU in rodents. In the present study, we used EAU not only as a model for autoimmune disease, but also as a paradigm for assessing the efficacy of OCT to visualize and monitor progressive changes in the retina and uvea in vivo, in brown Norway (BN) rats immunized with IRBP. The in vivo OCT images from different time points were compared with those obtained ex vivo by histopathology. The close correlation of OCT findings with histopathological scoring demonstrates the potential for OCT as a method for non-invasive monitoring of inflammatory diseases affecting the posterior segment of the eye. Furthermore, we show that OCT is sufficiently sensitive to perform diagnostic scoring during longitudinal studies of EAU.

Section snippets

Animals

Female BN rats (Charles River, Sulzfeld, Germany), 8–10 weeks of age, were used throughout the study and kept under environmentally-controlled conditions without the presence of pathogens. All experiments were approved by the local authorities of Braunschweig, Germany.

Induction of EAU

Rats were anaesthetized by inhalation of diethylether and injected intradermally at the base of the tail with a total volume of 200 μl inoculum, containing 50 μg IRBP (amino acids 521–540) (Donoso et al., 1989) in saline

OCT imaging of the healthy rat retina

A comparison between OCT images and the respective HE stained retinal sections in healthy adult BN rat retinas was made (Fig. 2). RT measurements were obtained from age and sex-matched animals at the ROI close to the optic nerve head.

In the OCT images, the non-reflective vitreous was clearly distinguished from the backscattering retina. All retinal layers could be observed and were identified in combination with histological sections (Fig. 2A, B). The RNFL and the retinal ganglion cell layer

Discussion

In this study, we have established OCT as a sensitive and valuable in vivo imaging technique to visualize inflammatory changes within the rat eye and monitor the disease course of EAU. Having correlated OCT images with histology of the healthy rat retina, we were able to detect subtle pathological changes during the early stages of EAU. Moreover, the monitoring of RT throughout the disease course revealed that this parameter is especially useful in discriminating between the different stages of

Grant numbers and sources of support

Gemeinnützige Hertie-Stiftung (grant no. 1.01.1/02/007) IG was supported by Ministry of Science, Republic of Serbia, (grant No. III41007).

Acknowledgements

We thank Nadine Meyer, Ina Boger and Marika Dienes for excellent technical support.

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