Volume and composition of reflux after intravitreal injection

Area of Science:

• Ophthalmology
• Drug Delivery
• Ocular Anatomy

Background:

• Intravitreal injections are common for delivering therapeutics to the posterior segment of the eye.
• Concerns exist regarding drug loss through reflux and subconjunctival bleb formation after intravitreal injections.
• Quantifying drug loss is crucial for optimizing treatment efficacy and understanding injection dynamics.

Purpose of the Study:

• To precisely measure the volume of drug lost through reflux after pars plana injections in human cadaver eyes.
• To investigate the impact of varying intraocular pressures (IOP) on drug loss during these injections.

Main Methods:

• Eight human cadaver eyes were used, divided into normal (15 mmHg) and high (30 mmHg) IOP groups.
• A standardized volume (50 μL) of hematoxylin dye was injected via the pars plana.
• Reflux was collected on Schirmer's test strips, scanned, and analyzed to calculate dye volume and total reflux volume.

Main Results:

• The average total reflux volume was 1.68 μL, with an average refluxed dye volume of 0.37 μL.
• On average, only 0.74% of the injected dye was lost, with a median loss of 0.15%.
• The range of dye loss was 0% to 4.30%, indicating minimal drug loss across tested conditions.

Conclusions:

• Pars plana injections result in a very small amount of injected therapeutic agent loss through reflux.
• The findings suggest that concerns about significant drug loss via reflux may be overstated.
• This quantification is valuable for understanding intravitreal injection outcomes and potential drug delivery efficiency.