Kinematic study of ozurdex injection in balanced salt solution: modeling the behavior of an injectable drug delivery...

To analyze the kinematics of a dexamethasone intravitreal implant, Ozurdex, after its injection in a balanced salt solution (BSS) at different release angles to simulate its movement in BSS/aqueous-filled eyes.

Eighteen Ozurdex implants were injected into a BSS-filled box at different release angles (15°, 30°, 45°), using 6 implants/group. The movement of injected implants was recorded by a high-speed video camera. Each implant's trajectory was graphically demonstrated by plotting over time. By using a distance-time function graph, the implant's velocity and normalized energy were calculated.

The high-speed video revealed that implants injected at 15° followed a more horizontal trajectory compared to those injected from 30° and 45°, respectively. The implant injected at 15° also achieved the highest mean initial velocity and mean initial normalized energy. The implant velocity from each injection angle decreased exponentially over time and reached nearly zero at 0.1 s. An injection of the implant at a flatter angle was also associated with higher mean retinal impact normalized energy.

An implant injected at a flatter angle tends to travel farther in the horizontal plane and has more initial velocity, which theoretically generates higher initial normalized energy and retinal impact normalized energy. The accidental injection at a flatter angle, which results in shortening of the effective travel distance, may carry the potential risk of direct retinal injury from the injected implant. The amount of energy necessary to cause direct retinal injury, and whether this would be clinically significant, requires further study.