Intravitreal Injection of Triamcinolone Acetonide into Healthy Rabbit Eyes Alters Retinal Function and Morphology

Aim: To study the effects of intravitreally injected triamcinolone acetonide (TA) and/or its preservative benzyl alcohol (BA) in healthy rabbit retina. Methods: Forty-eight rabbits (aged 4 months, body weight approximate to 3 kg) were randomized into four groups (n=12). They were examined with electroretinography (ERG) prior to drug exposure, and then injected intravitreally with a combination of TA and BA, TA without BA, BA alone or a balanced saline solution (BSS). The electroretinograms were assessed 1 week and 7 weeks post-injection. The rabbits were euthanized and the sectioned retinas were studied. Immunohistochemical analysis was performed on rods, cones, rod bipolar cells, horizontal cells, amacrine cells and Muller cells. Results: Rabbits injected with BA showed a significantly lower rod-mediated b-wave amplitude than the controls 1 week after injection. TA-injected rabbits demonstrated significantly higher a- and b-wave amplitudes in the total retinal response than the controls 1 week post-injection. The rabbits injected with TA+BA demonstrated a significantly higher b-wave amplitude in the total retinal response than the controls 1 week after injection. The significantly higher a-wave amplitude in the total retinal response remained in the TA-injected rabbits 7 weeks after injection. Immunohistochemistry revealed that protein kinase C alpha (PKC alpha) was down-regulated in both the perikarya and the axons of bipolar cells in histological sections from rabbit retina injected with TA+BA, BA and TA. Conclusions: Intravitreal injection of the preservative BA reduces the isolated rod-mediated retinal response in the rabbit, transiently and selectively. Intravitreal injection of TA increases the total retinal response in the rabbit up to seven weeks after injection. The effects observed are not only limited to retinal function, but also include changes in the expression of PKC alpha in rod bipolar cells, indicating drug-related interference with normal retinal physiology in the healthy rabbit eye.