Purpose  

To assess retinal toxicity of the vehicle of triamcinolone, benzyl alcohol (BA), when injected into the vitreous cavity of rabbits.

Methods  

This prospective comparative experimental study included 24 pigmented rabbits assigned into two groups: group 1 (experimental, n = 12) received intravitreal 0.1 ml of BA, and group 2 (control, n = 12) received intravitreal 0.1 ml of balanced salt solution (BSS); all injections were done in the right eyes. Clinical examinations [slit lamp biomicroscopy, indirect ophthalmoloscopy, and three intraocular pressure (IOP) measurements] were done on both eyes before injection, at 1 and 3 h post injection, together with electroretinograms (ERGs) at 3 days, 1, 2, 4, and 6 weeks following injections. Three rabbits from each group were euthanased at 1, 2, 4, or 6 weeks and eyes were sent for light and electron microscopic examination for quantitative morphometric measurements.

Results  

The mean amplitudes of the a and b waves of the BA-injected eyes were 6.42 ± 9.02 μv and 11.18 ± 15.18 μv at 3 days, respectively, which were significantly reduced compared with the BSS-injected eyes (30.87 ± 8.22 μv and 57.90 ± 13.38 μv, respectively; P < 0.01 t-test) and the non-injected contralateral eyes (36.20 ± 7.85 μv and 64.10 ± 9.36 μv, respectively; P < 0.01 t-test). These ERG responses continued to be significantly reduced in the BA-injected eyes (P < 0.01 t-test) throughout the study period. The mean ganglion cell count was significantly reduced (P < 0.005 t-test) in the BA-injected eyes (8.42 ± 2.4) compared with the BSS- and non-injected eyes (16.42 ± 3.9 and 16.5 ± 4.2, respectively). The mean thicknesses of the inner nuclear layer (INL) and outer nuclear layer (ONL) were significantly reduced (P < 0.005 t-test) in the BA-injected eyes (3.78 ± 0.96 μm and 11.77 ± 1.29 μm, respectively) compared with the BSS- (6.1 ± 0.92 μm and 21.82 ± 0.95 μm, respectively) and non-injected eyes (7.05 ± 1.9 μm and 22.49 ± 1.01 μm, respectively). Electron microscopy showed moderate to severe intracellular changes in the ganglion cell layer, INL, ONL, and photoreceptor layer at 6 weeks in BA-injected eyes, with no significant changes in BSS-injected eye. There was no significant rise in the IOP or clinical evidence of increased lens density during the study period in any of the eyes.

Conclusions  

Triamcinolone acetonide’s vehicle, BA, produced severe ERG and structural damage to the retina when injected intravitreally.