A system for producing controlled elevation of intraocular pressure in awake Brown Norway rats

Animal models that help us understand how elevated intraocular pressure (IOP) causes axonal injury will lead to new glaucoma therapies. Because reliable measurements are difficult to obtain in chronic models, we developed the controlled elevation of IOP (CEI) approach. Here, a cannula connected to an elevated balanced salt solution (BSS) reservoir is inserted into the anterior chamber of anesthetized Brown Norway rats. The extent and duration of IOP exposure is controlled by adjusting the reservoir height. We now describe a method for creating CEI in awake animals. A Pinport, which has a silicone plug that can be penetrated repeatedly, is modified, attached to the skull, and connected to a microcannula that is implanted in the posterior chamber. To elevate IOP, BSS from a reservoir is allowed to flow through a pressure transducer to a swivel-mounted tether and injector. The injector is placed on the Pinport, bypassing the need for anterior chamber cannulation and general anesthesia during CEI. The surgical technique and equipment required for implantation are described, as well as the equipment and methods for performing awake CEI in several animals at a time. The ability of this system to control the level of IOP is demonstrated by TonoLab measurement, and by comparing reservoir (Pinport) pressures to direct measurement using an independent anterior chamber cannula and transducer. We also demonstrate that IOP elevation can be maintained over several hours. Specific pitfalls during and after surgical implantation are highlighted to help other researchers adopt these techniques.