Effective intracameral injection in the mouse model

Abstract

Purpose : Intraocular injection is a standard route of administration for the treatment of several eye diseases, including AMD, intraocular inflammation, infection, and gene therapy. In human subjects, intracameral injection is rapid and easy to perform, with minimal discomfort for the patient. However, in the murine model these injections are more challenging due to dimension and anatomy of the eye. Our goal was to develop a semi-automated procedure for safe intracameral injection improving precision and reproducibility in the mouse model.

Methods : A 3D printed plate was developed to safely stabilize the body and immobilize the head of the animal. A color camera and an optical coherent tomography (OCT) system were adapted for injection real-time monitoring. Needles were mounted on a Hamilton syringe fixed on a 4-axis motorized manipulator for precise positioning. In vivo experiments were performed under general anesthesia (IP ketamine 60mg/Kg and Medetomidine 1mg/Kg), while animal's temperature was maintained at 37C. A perforated Tegaderm was applied to the periocular region to recline lashes and partially protrude the globe. Microneedles of various sizes (31-35G) and laser-tailored tip profiles (30 to 14°) as well as different puncture site orientations and speeds of injection were tested. Intracameral injections consisted of 0.4 µL of either BSS or OCT contrast agent. Recorded videos were used to estimate the best injection conditions.

Results : Adult C57Bl/6 mice (20 ex vivo, 6 in vivo) were used. Most successful injections were performed with a custom tri-surface 14° 35G laser-sharpened needle (Fig. 1a). Injections at the iridocorneal angle, tangential to the limbus resulted in effective piercings with less distortion of the globe. By using acute bevel angles facing the endothelium, less damage to the iris and lens, and less bleeding and leaking were reported (Fig. 1b-c). Implementation of a semi-automatic system with real-time monitoring ensued in reproducible results (Fig. 1d).

Conclusions : Implementation of a semi-automatic system under real-time OCT monitoring using tailored needle tip profiles allowed successful and safer intracameral injection in mice. Such setup is suggested to increase precision and reproducibility in murine models.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1. Intracameral injection for murine models. a) 14° 35G laser-cut microneedle; b) OCT image of successful injection; c) Color image of a pierced cornea; d) Semi-automatic system for intracameral.