Do Intravitreal Injections Induce Retinal Damage?

Abstract

Purpose:: Intravitreal injections are used as administration routes for the treatment of different ocular diseases such as age related macular degeneration, macular oedema and endophthalmitis, with the recent introduction of therapy protocols requiring repeated and frequent injections of volumes up to 250 µl . However, the consequences of intravitreal injections themselves on the retina has not been previously assessed. The purpose of this study was to investigate the effect of sterile saline injections on retinal ganglion cell (RGC) apoptosis in vivo.

Methods:: DA rats underwent general anaesthetic following which varying volumes of sterile saline were administered at the same time as fluorescent-labeled annexin 5 using our recently established DARC (Detection of Apoptotic Retinal Cells) imaging method. Eyes were randomized to 3 different injected volumes (n=6 each) of 1, 2 and 4 µl. Eyes were imaged 2 hours after injections, following which montages from single images were obtained and apoptosing cells identified and counted, and a RGC density/unit area calculated.

Results:: The range of volumes were extrapolated from clinical studies to the rat (maximally 250 µl injection in 4 ml human vitreous equivalent to 3.75 µl in 60 µl rat vitreous). All intravitreal injections induced RGC apoptosis. The volume injected was positively correlated to the level of RGC apoptosis (R² = 0.995) with mean RGC apoptosis density (cells per square micron ± 95%, CI) calculated as 71.2 E-06±23.03, 88.3 E-06±17.12 and 114.4 E-06±39.42 in 1 µl, 2 µl and 4 µl groups respectively. Most of the apoptosis at these volumes appeared related to the injection site, in the superior retina.

Conclusions:: This study demonstrates that intravitreal injections can cause retinal damage, as measured by RGC apoptosis. Furthermore, the level of damage appears related to the injected volume. These findings have profound implications to ocular therapy design and administration of intravitreal treatments. Further work is underway to investigate the role of intraocular pressure, long-term effects and possible mechanisms involved in this process.

Keywords: apoptosis/cell death • injection • imaging/image analysis: non-clinical