Learning curve of a trained vitreo-retinal surgeon in sub-retinal injections in a rat model: Implications for future clinical trials.

Purpose: The sub-retinal injections are not very commonly performed procedures in vitreoretina, but form a crucial step in any cell replacement therapy for retinal diseases. The purpose of this study is to describe the learning curve of a trained vitreo-retinal surgeon in sub-retinal injections in a rat model and its implications in future clinical trials. Methods: This is an in-vivo retrospective animal study using Wistar rats. All ARVO guidelines regarding animal handling were followed. After anesthetization, aspectic preparation and dilating the pupils with 1% tropicamide eye drops, subretinal injection of 10 μl saline was done via a limbal entry. Data recorded included time taken for the procedure, success of injection, associated complications, post-operative infections and complications. The rats were followed up for 1 month post procedure. A trend analysis was done for the above factors to look for improvement in ease of procedure, reduction in procedure time and reduction in complications for the clinician using a novel objective scale. Results: About 20 eyes were studied. Mean weight of the rats was 188 ± 12.82 gram. Mean time taken for the procedure was 14.1 ± 5.07 minutes. There was a significant inverse co-relation between the serial number of the eye and time taken for the procedure (r = -0.89, P < 0.0001). Comparative complications noted between the first ten and the last ten eyes were: conjunctival tear 30% versus 10% (P = 0.27), lens touch 50% versus 10% (P = 0.05), subretinal hemorrhage 40% versus 0% (P = 0.13), vitreous loss 30% versus 0% (P = 0.06). The successful subretinal injection without intraocular complications was achieved in 40% versus 90% (P = 0.02). There was a significant co-relation between the serial number of the eye and ease of the procedure (r = 0.87, P < 0.0001). Post operatively none of the eyes had any infection. Six eyes (12%) developed cataract and 3 eyes (6%) had non-resolving retinal detachment at the last examination visit. Conclusion: Subretinal injections in rats have a definite learning curve even for a trained vitreoretinal surgeon. This should be accounted for and resources allocated accordingly to achieve good technical comfort and negate confounding by the surgeon factor in the results of future clinical trials.