kinematics of novel intravitreal steroid implant injector in simulated vitrectomized and non-vitrectomized eyes

Abstract

Purpose : Intravitreal implants are routinely used for depots of sustained drug delivery. Injections of current market devices have been reported to cause retinal hemorrhages and macular holes from direct mechanical forces during injection. We provide kinematic analysis in simulated vitreous and saline to confine the range of safe injection velocities from novel intravitreal implant delivery devices.

Methods : 10 proprietary Aerie Pharmaceutical intravitreal delivery systems were recorded at 240 frames-per-second at 1024×1024 pixel resolution. 396μg implants of dimensions 265 x 265 x 4500μm were injected with fast and slow velocities into an open top chamber at room temperature and pressure. 4 implants were launched with slow velocity into normal saline. 4 implants were launched with high velocity into vitreous substitute - hyaluronic acid 1%. 2 implants were launched with high velocity into saline. Empiric initial velocity coming out of the injector barrel (v_o) was derived by launching implants straight vertically into air and assumed negligible air resistance. Adult eye retina to retina diameter is assumed to be between 19.4mm to 25.8mm (22.9mm average).

Results : Injection velocity (v_o) was 3431 ± 50 mm/s for fast injections. The 4 slow velocity injections delivered the implants exactly at the site of injection in both media. In hyaluronic acid, fast injections delivered implants to a maximum displacement (x_max) of 16.7 ± 3.2 mm in 25 ± 5ms. In saline, fast injections delivered implants to x_max of 28.5 ± 5 mm in 50ms.

Conclusions : Slow speed injections would likely be best used for local implant placement (at site of injection) in any medium. V_o of 3431 mm/s is approximately the upper limit of injection velocity for these implants in non-vitrectomized eyes as the x_max range encompasses maximum retina-to-retina distance, however could be further optimized to account for injection angles that direct toward shorter paths. Smaller v_o should be used for vitrectomized eyes as modeled by saline. Empiric drag coefficients for these implants would help calculate force transmitted to the retina upon contact.

This is a 2021 ARVO Annual Meeting abstract.