2023 Volume 10 Issue 4 Pages 157-167
Intravitreal (IVT) injections are the current method for retinal drug delivery and have been widely used in humans, although it is well known that IVT injections often cause an increase in intraocular pressure (IOP) that closely relates to the injection volume. Because of the anatomical and physiological similarities of the monkey and human eye, cynomolgus monkeys are often used for preclinical studies on new treatments using large molecules or gene therapy requiring IVT application. However, there is only limited information on the maximal dosing volume for IVT injections in cynomolgus monkeys. To determine an appropriate maximal dosing volume for IVT injections, comprehensive ocular examinations were conducted in IVT-injected eyes of cynomolgus monkeys. Up to a dosing volume of 150 µL/eye by IVT injection, there were no IVT injection-related ocular findings in pupillary light reflex gross observations, slit lamp biomicroscopic and indirect ophthalmoscopic and fundus autofluorescent examinations, intraocular pressure, optical coherence tomography of the anterior and posterior segments of the eye, axial length measurement, electroretinogram waveforms, or histopathological examinations of treated eyes. However, leakage of the dosing solution from an eye was observed at 150 µL/eye, indicating a technical limitation for the maximal applicable volume. In addition, recovery from IOP elevation immediately after injection of 150 µL/eye was slower than after injections of 50 or 100 µL/eye. Therefore, we recommend a maximal volume of 100 µL/eye for IVT injections in cynomolgus monkeys.