A Novel Method for the Measurement of Reflux from Intravitreal Injections: Data from 20 Porcine Eyes

Background: Reflux following intravitreal injection is a common phenomenon, but it is unknown how much, if any, medication is lost as a result. Reflux is known to be a combination of vitreous and the injected agent, but the relative composition is unknown. This article describes a novel method for the measurement of the volume and composition of reflux and presents data from porcine eyes. Methods: Twenty porcine eyes were injected with 0.05 ml of dye at intraocular pressures (IOPs) of 15, 20, 25 and 30mmHg (five eyes per subgroup). Reflux was captured on filter paper and the area of saturation and color intensity of the dye were digitally analyzed. Total refluxed volume and proportion of dye versus vitreous fluid were calculated from linear regression lines created from known standards. Results: Average (median) total volume of reflux from all eyes was 1.19 mu l (0.93 mu l), volume of injected dye refluxed was 0.47 mu l (0.11 mu l) and composition of reflux was 20.8% dye (15.5%). Less than 1% of the injected dye was lost to reflux. There were no differences between IOP groups in the total volume refluxed, the total amount of dye refluxed, the average composition of the reflux or the amount of injected dye refluxed (df = 3 for all comparisons; p = 0.58, p = 0.51, p = 0.55, p = 0.51, respectively). Conclusions: This novel method allows for measurement of quantity and composition of reflux following intravitreal injection in vitro. While reflux occurs frequently, it is predominantly composed of vitreous, not the injected agent. In fact, <1% of the original injection was lost to reflux.