Neuroprotective effects of intramuscular ketamine in rabbit retinas after pars plana vitrectomy and silicone oil injection

PURPOSE: To investigate potential retinal neuroprotective effects of intramuscular ketamine in rabbits after pars plana vitrectomy (PPV) and intravitreal silicone oil injection (SOI). METHODS: Twelve New Zealand rabbits (weight, 2.0-2.5 kg) underwent PPV with SOI in the right eye. Postoperatively, six rabbits received a daily intramuscular injection of ketamine for 4 weeks (ketamine-operated eyes), and six rabbits received a daily intramuscular injection of saline (saline-operated eyes). The retina from the left eye of each rabbit served as a control (ketamine-control and saline-control eyes). The animals were euthanized at 4 weeks after surgery. Qualitative and quantitative analyses were performed using the Zeiss Axiophot microscope and KS 400 software. RESULTS: Qualitative analysis using light microscopy demonstrated more extensive edema and cell disorganization in saline-operated retinas than in ketamine-operated, ketamine-control, and saline-control retinas. Quantitatively, the cell densities (cell/mm) in the outer nuclear layer (ONL), inner nuclear layer (INL), and ganglion cell layer (GCL) in saline-operated retinas were significantly (P < 0.05) lower than those in these layers in ketamine-operated, ketamine-control, and saline-control retinas. The cell density in the ONL in saline-operated retinas was 52% lower than that in ketamine-operated retinas, 55% lower than that in ketamine-control retinas, and 56% lower than that in saline-control retinas. The cell density in the INL in saline-operated retinas was 44% lower than that in ketamine-operated retinas, 48% lower than that in ketamine-control retinas, and 49% lower than that in saline-control retinas. The cell density in the GCL in saline-operated retinas was 60% lower than that in ketamine-operated retinas, 64% lower than that in ketamine-control retinas, and 64% lower than that in saline-control retinas. CONCLUSION: PPV with SOI was associated with retinal cell death and disorganization in rabbit eyes. Intramuscular ketamine administration provided protection against these effects.