An Experimental Study On Morphological Changes Induced By Intravitreal Triamcinolone Acetonide And Its Vehicle In Rabbit Retina

ObjectiveTo respectively evaluate the morphological changes induced by intravitreal administered triamcinolone acetonide (TA) crystals and vehicles from two commercial injections at different doses and volumes.Materials and MethodsPurified crystal A, B and vehicle A, B were abstracted from two commercial TA injections by centrifugation.(1) Twenty-three New Zealand white rabbits were intravitreally injected on the right eyes, respectively with crystal A at 4mg, 20mg and 40mg, crystal B at 4mg and 20mg, and balanced salt solution (BSS at 0.1ml and 0.2ml. At given time points, fundus was examined by ophthalmoscope. Retinal structure was analyzed by light microscope (LM) at 4 and 8 weeks post-injection (pi), and transmission electron microscope (TEM) at 8 weeks pi.(2) Thirty-six New Zealand white rabbits were intravitreally injected on the right eyes, respectively with vehicle A, B and BSS at 0.1ml or 0.2ml. At given time points, fundus was examined by ophthalmoscope, and vascular damage was identified by fluorescein angiography (FA). Retinal structure was analyzed by LM at 2, 4 and 8 weeks pi, and TEM at 8 weeks pi.Results(1) In eyes injected with TA, none of the eyes showed abnormalities in anterior segments and fundus. LM showed that in eyes injected with crystal B, photoreceptor layer, inner nuclear layer (INL) and ganglion cell layer (GCL) showed varied degrees of damages at 4 and 8 weeks pi. TEM showed that in eyes injected with crystal A, although photoreceptor discs appeared slightly edematous at 20mg and 40mg, the mitochondrial and nuclear structure appeared well preserved. Additionally, the mitochondrial morphology even appeared more orderly arranged and better defined as dose increased. In eyes injected with crystal B, photoreceptor damages were shown as disc edema, mitochondrial destruction, and nuclear pyknosis and karyolysis, and were more obvious as dose increased.(2) In eyes injected with vehicles, none of the eyes showed abnormalities in anterior segments. Vascular narrowing and myelinated fiber edema were shown ophthalmoscopically in eyes injected with vehicle B. The vascular damages were further confirmed by FA. LM showed damages in photoreceptor layer, INL, and GCL in eyes injected with vehicle A, and more extensive damages and local necrosis in eyes injected with vehicle B. TEM showed damages in photoreceptor discs and mitochondria in eyes injected with both vehicles, and nuclear pyknosis and karyolysis in eyes injected with vehicle B. The vascular and retinal damages became obvious as volume increased.Conclusions(1) Purified crystal A up to 40mg might produce slight damage to photoreceptor discs, but potential protective effects on photoreceptor mitochondria. Crystal B at 4mg and 20mg produced obvious retinal toxic effects on retinal structure and photoreceptor ultrastructure, which might be induced by vehicle components or contaminants that could hardly be eliminated through centrifugation.(2) The two vehicles produced toxic effects in rabbit eyes at 0.1ml and 0.2ml. The damages might be volume-related. These findings suggest that vehicles should be reduced or decanted before intravitreal application. Vehicles free of retinal-toxic ingredients are expected.