Mouse Fundus Examination Using OCT And Computer Automated Segmentation Based On OCT Images

Because of the high similarity with human genotypes, mice are widely used in medical studies as experimental models, as well as in basic ophthalmological studies. Therefore, a mature and reliable measurement technique for the mouse retina is of great significance in studies of animal models of eye disorders. However, the current need to sacrifice animals for histological examinations at different time points interferes with the ability to follow the disease process and to monitor therapeutic or side effects over time in the same individuals. To obtain an improved observation of mice retinopathy and to reduce the sacrifice of mice, a novel measurement of the mouse retina in vivo is of highly practical significance. Optical coherence tomography (OCT), allows for the noninvasive in vivo cross-sectional imaging of ocular structures such as the retina, the retinal nerve fiber layer (RNFL), and the optic nerve head. OCT has evolved over the past two decades to become an important diagnostic tool in clinical and experimental ophthalmology. With no damage, cell-level resolution, fast imaging and precise quantitative measurement, using the OCT in studies of the mouse retina in vivo may be a good solution. Because refractive systems of mice are quite different from humans, clinical OCT cannot be directly applied to the retina of mice. Here, we use a modified combination of lenses which makes the system simpler and easier for the mouse retina recorded by Zeiss HD-OCT. High-resolution, wide-angle tomographic images of the mouse retina were acquired by this OCT system. For the first time, we describe a novel method of measuring the magnification of the OCT system. In addition, combined with the function of the quantitative measurement tools in OCT software, the system is convenient for obtaining the retinal thickness at any position in the mouse retina, even a specific layer of the retina such as RNFL. Through a training set of experiments, the magnifications of the OCT optical system are determined. The statistical analysis demonstrates that the lengths that are measured by OCT are 4.46 times as large as the actual lengths that are transversely measured in stretched preparations of the mouse choroid and scleral complex by microscope. Meanwhile, the ratio of the data that are axially measured by histological sections and OCT is approximately equal to 1, which is a strong support for the conclusion that there is barely axial magnification using the OCT optical system through OCT. We proved that this novel method of multi-parameter measurements for the mouse retina in vivo can replace the traditional measuring method of histological sections and is more suitable for the needs of basic retinal studies. Different modes within the OCT device had been chosen to obtain the average thickness of the mouse retina and the retinal volume simultaneously, as well as the RNFL thickness. In addition, an improved computer algorithm was used to obtain the choroid thickness by automated segmentation based on high-definition OCT images.