Application of Optical Coherence Tomography to a Mouse Model of Retinopathy

Published: January 12, 2022

doi:

Xiaoting Mai*¹, Shaofen Huang*¹, Wen Chen, Tsz Kin Ng^2,3, Haoyu Chen

¹Joint Shantou International Eye Center,Shantou University and the Chinese University of Hong Kong, ²Shantou University Medical College, ³Department of Ophthalmology and Visual Sciences,the Chinese University of Hong Kong

Summary

Here, we describe an in vivo imaging technique using optical coherence tomography to facilitate the diagnosis and quantitative measurement of retinopathy in mice.

Abstract

Optical coherence tomography (OCT) offers a noninvasive method for the diagnosis of retinopathy. The OCT machine can capture retinal crosssectional images from which the retinal thickness can be calculated. Although OCT is widely used in clinical practice, its application in basic research is not as prevalent, especially in small animals such as mice. Because of the small size of their eyeballs, it is challenging to conduct fundus imaging examinations in mice. Therefore, a specialized retinal imaging system is required to accommodate OCT imaging on small animals. This article demonstrates a small-animal-specific system for OCT examination procedures and a detailed method for image analysis. The results of retinal OCT examination of very-low-density lipoprotein receptor (Vldlr) knockout mice and C57BL/6J mice are presented. The OCT images of C57BL/6J mice showed retinal layers, while those of Vldlr knockout mice showed subretinal neovascularization and retinal thinning. In summary, OCT examination could facilitate the noninvasive detection and measurement of retinopathy in mouse models.

Introduction

Optical coherence tomography (OCT) is an imaging technique that can provide in vivo high resolution and crosssectional imaging for tissue¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸, especially for the noninvasive examination in the retina⁹^,¹⁰^,¹¹^,¹². It can also be used to quantify some important biomarkers, such as retinal thickness and retinal nerve fiber layer thickness. The principle of OCT is optical coherence reflectometry, which obtains crosssectional tissue information from the coherence of light reflected from a sample and converts it into a graphic or digital form through a computer system⁷. OCT is widely used in ophthalmology clinics as an essential tool for diagnosis, follow-up, and management for patients with retinal disorders. It can also provide insight into the pathogenesis of retinal diseases.

In addition to clinical applications, OCT has also been used in animal studies. Although pathology is the gold standard of morphological characterization, OCT has the advantage of noninvasive in vivo imaging and longitudinal follow-up. Furthermore, it has been shown that OCT is well correlated with histopathology in retinopathy animal models¹¹^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰. The mouse is the most commonly used animal in biomedical studies. However, its small eyeballs pose a technical challenge to conducting OCT imaging in mice.

Compared to the OCT first used for retinal imaging in mice²¹^,²², OCT in small animals has now been optimized with respect to hardware and software systems. For example, OCT, in combination with the tracker, significantly reduces the signal-to-noise ratio; OCT software system upgrades allow more retinal layers to be detected automatically; and the integrated DLP beamer helps to reduce the motion artifacts.

Very-low-density lipoprotein receptor (Vldlr) is a transmembrane protein in endothelial cells. It is expressed on retinal vascular endothelial cells, retinal pigment epithelial cells, and around the outer limiting membrane²³^,²⁴. Subretinal neovascularization is the phenotype of Vldlr knockout mice²³. Therefore, Vldlr knockout mice are used to investigate the pathogenesis and potential therapy of subretinal neovascularization. This article demonstrates the application of OCT imaging to detect retinal lesions in Vldlr knockout mice, hoping to provide some technical reference for retinopathy research in small animal models.

Protocol

The operations were performed following the Statement on the Use of Animals in Ophthalmic and Vision research from the Association for Research in Vision and Ophthalmology. The experimental design was approved by the institutional animal Ethics Committee (Medical Ethics Committee of JSIEC, EC 20171213(4)-P01). Two-month-old C57BL/6J mice and Vldlr knockout mice were used in this study. There were 7 mice in each group, all of which were female and weighed 20 g to 24 g. 1. Experimental co…

Representative Results

Thanks to the high-resolution scans of OCT, the layers of the mouse retina can be observed, and abnormal reflections and their exact locations can be identified. The retinal OCT images of Vldlr knockout mice and C57BL/6J mice were compared in this study. The OCT images of all C57BL/6J mice showed various retinal layers with different reflectivity, and the demarcation was clear (Figure 8D). In contrast, all Vldlr knockout mice showed abnormal, hyperreflective lesions on the …

Discussion

In this study, OCT imaging using a small-animal retinal imaging system was applied to evaluate retinal changes in Vldlr knockout mice, which demonstrate incomplete posterior vitreous detachment, subretinal neovascularization, and retinal thickness thinning. OCT is a noninvasive imaging method to examine the condition of the retina in vivo. Most OCT devices are designed for human eye examination. The size of the hardware equipment, the setting of the focal length, the setting of the system parameters, an…

Disclosures

The authors have nothing to disclose.

Acknowledgements

Project Source: Natural Science Foundation of Guangdong Province (2018A0303130306). The authors would like to thank the Ophthalmic Research Laboratory, Joint Shantou International Eye Center of Shantou University and the Chinese University of Hong Kong for funding and materials.

Materials

100-Dpt contact lens	Volk Optical,Inc, Mentor, OH		Accessory belonging to the RETImap
Double aspheric 60-Dpt glass lens	Volk Optical,Inc, Mentor, OH		Accessory belonging to the RETImap
Electric heating blanket	POPOCOLA	CW-DRT-01	50 x 35 cm
Injection syringe (1 mL)	Kaile		0.45 x 16RWLB
Levofloxacin Hydrochloride Eye Gel	EBE PHARMACEUTICAL Co.LTD		5 g: 0.015 g
Medical sodium hyaluronate gel	Alcon	16H01E
Microliter syringes	Shanghai high pigeon industry and trade co., LTD	Q31/0113000236C001-2017	50 µL
Povidone iodine solution	Guangdong medihealth pharmaceutical Co.,LTD		100 mL
RETImap	ROLAND CONSULT	19-99_50-2.1_1.2E	cSLO/ERG/VEP/FA/OCT/GFP
Small animal ear studs	OSMO POCKET OT110	INS1005-1S
Tropicamide Phenylephrine Eye Drops	Santen Pharmaceutical Co.,LTD		5 mg/mL
Xylazin	Sigma	X1251-5G	5 g
Zoletil 50	Virbac.S.A	7FRPA	Tiletamine 125 mg + Zolazepam 125 mg

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Mai, X., Huang, S., Chen, W., Ng, T. K., Chen, H. Application of Optical Coherence Tomography to a Mouse Model of Retinopathy. J. Vis. Exp. (179), e63421, doi:10.3791/63421 (2022).