Abstract
Purpose :
Consistently achieving free-hand intra-retinal injection remains an insurmountable task. Factors contributing to the lack of micron scale precision include human limitations in: dexterity, visual resolution, hand tremor and movement of the target retina. We hypothesize that a precision micro-injector, integrated with a common–path optical coherence tomography (CP-OCT) fiber probe as a distance sensor, would overcome these limitations. .
Methods :
Free hand intraretinal injection was performed using a CP-OCT sensor guided “SMART” 32 gauge microinjector into the retina of freshly enucleated bovine eyes. The CP-OCT sensor is able to “visualize” and track the location of individual retinal layers in real time. The needle tip position is controlled by a high-speed linear motor. Four investigators, two with microsurgical experience (E1 and E2) and two novices (U1 and U2) performed injections using the SMART micro-injector with and without automatic depth control assistance. Each performed six consecutive injections with indocyanine green (ICG) targeting the photoreceptor layer.
Results :
Using the SMART microinjection system with automatic depth control, E1 and U1 were able to rapidly and accurately inject ICG solution into the photoreceptor layers. The target volume was 5 nL for each injection and the actual average injection volume was 3.7 nL±1.4nL (for E1) and 3.5nL ±1.2nL (for U1). The average injection depth was 317mm ±36.8mm (for E1) and 407mm±28.3mm (for U1). Figure below shows raw OCT images of a successful intraretinal injection. Both E2 and U2 without automatic depth control failed to achieve any ICG injection into the photoreceptor layers. In most of the failed attempts, the needle tip penetrated the retina resulting in subretinal injection.
Conclusions :
Our results are consistent with our hypothesis that a CP-OCT guided SMART microinjector would enable precise intraretinal injections. Experienced and inexperienced users were able to perform this task with SMART tool assistance however, neither inexperienced nor experienced users were able to perform the task without tool assistance. Precise intraretinal injection into diseased retina with abnormal layers may be problematic and requires further study.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.