Application of a new subretinal injection device in the dog

The use of a new subretinal injection device (RetinaJect Subretinal Cannula, SurModics, Inc., Eden Prairie, MN) to access the subretinal space in the canine model was evaluated. Subretinal injections were performed in 33 mongrel dogs between 2 and 52 months of age (median = 9 months). In 5 normal dogs the injection of 150 microl saline or India ink occurred by using a conventional subretinal injection device (CSID) with a 30-gauge anterior chamber irrigating cannula. The sclera had to be surgically exposed and penetrated before the subretinal injection with the CSID could occur. After removing the CSID, the conjunctiva over the sclerotomy site had to be closed. In a second group of 28 dogs [16 normals, 10 RPE65 mutants, and 2 with progressive rod cone degeneration (prcd)], the 25-gauge needle of the RetinaJect was used to penetrate the conjunctiva and the sclera. Once the tip of the needle was close to the retinal surface, a 39-gauge polyimide cannula was extended and brought into apposition with the retina for the subsequent subretinal injection of 150 microl saline, India ink, or adeno-associated virus (AAV). No closure of the conjunctiva was required. The animals were clinically monitored between 1 and 59 weeks after surgery. From this second group 25 eyes were harvested for routine histological analysis either immediately after surgery or after a clinical observation time of between 1 and 40 weeks. Both devices provided equally successful access to the subretinal space. The main advantage of the RetinaJect was that no surgical dissection was required; this led to a shorter procedure time and milder postoperative conjunctival swelling. In summary, the use of the RetinaJect can be recommended as an alternative to the CSID for subretinal injections in dogs.