SUMMARY – IN VIVO TESTING AND INSTRUMENTATION MODULE The In Vivo Testing and Instrumentation (IVTI) module provides our participating faculty with a comprehensive suite of resources to speed up the pace of discovery for their in vivo investigations. These resources span imaging, mechanical, and optical equipment with accompanying usage expertise and design guidance. In vivo testing, both with commercial and custom instrumentation, is essential for many of the lines of investigation pursued by our participating faculty. As advances in optical imaging, microelectronics, and neuroengineering continue to accelerate, the lines between these formerly distinct research silos begin to blur. The IVTI module provides both early-stage and more established investigators with the equipment, training, and resources to evaluate visual system structure and function with both conventional and customized instrumentation. The IVTI module gives access to equipment and training in the in vivo measurement of retinal structure and function. When these existing tools are insufficient for the needs of our investigators, the IVTI module directors will guide and train on the conception, development, and design of custom research devices to meet the needs of our participating faculty. Once a design has been developed, the IVTI module will also provide state-of-the-art resources to fabricate the new device, as well as expert advice along the way to maximize the likelihood of success. Taken together, these resources will allow our participating faculty at the University of Pittsburgh and Carnegie Mellon University to access a modern toolkit for in vivo testing, providing both established tools and a rapid prototyping mechanism to develop the next generation of in vivo testing and instrumentation that will drive future discoveries.