Slit–Lamp Based Fundus Imaging and Optical Coherence Tomography of the Rat and Mouse Retina

Abstract

Abstract: : Purpose: To develop a small animal non–contact retinal imaging system capable of simultaneous fundus imaging and optical coherence tomography (OCT) of the rat and mouse retina. Methods: An imaging system consisting of a benchtop high–resolution time–domain OCT system and a slit–lamp based delivery head was designed. The delivery head consists of a Zeiss slit–lamp with video camera attachment and a 90D Volk lens mounted at a fixed distance from the slit–lamp objective. The lens delivers the OCT beam and provides an aerial image of the retina viewed through the slit lamp. A custom–made mouse table with high–precision three–axis, tilt and rotational adjustment was mounted on the head–rest to help position and align the mouse or rat eye. A reduced paraxial optical model of the mouse and rat eye was developed to calculate the retinal field of view, the size of the aerial image, the position of the entrance pupil, the focused OCT beam diameter and scan length on the retina. These parameters were used to select the power of the imaging lens, adjust the delivery of the slit–lamp illumination beam for fundus imaging, and design the OCT scanning system. A physical model of the mouse eye consisting of a plano–convex lens mounted on a PMMA substrate was constructed based on the paraxial data to test and calibrate the imaging system. Preliminary experiments were conducted on anesthetized C57BL mice and rat retina, as well as on enucleated eyes. Results: Using a 90D Volk lens, wide–field images of the retina of anesthetized C57BL mice were successfully recorded by a single operator. The images were of sufficient quality to be able to visualize the retinal nerve fibers. The system provides a retinal field of view of 2 mm in the physical model of the mouse eye. The OCT delivery system produces a 1.5 mm lateral scan on the retina of the model eye. Preliminary images of rat retinas were recorded. The sensitivity of the current system was sufficient to measure the retinal thickness in anesthesized rats. Conclusions: This study demonstrates the feasibility of mouse fundus and OCT imaging using a non–contact slit–lamp based system. Support: This work was supported in part by the generosity of the Wollowick Foundation; NIH center grant P30–EY014801; Research to Prevent Blindness; The Florida Lions Eye Bank; The Henri and Flore Lesieur Foundation, West Palm Beach, FL.

Keywords: imaging/image analysis: non-clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)