H&E staining of retinal tissue sections. Eyes were processed for X-gal staining at 3 different concentrations of viral vector dose at 1 week post-injection and counterstained with H&E. Controls (A) with no injection revealed no β-galactosidase activity and normal physiology. CMV LacZ injection at 1 × 107 vp/μL (B), 1 × 108 vp/μL (C), and 1 × 109 vp/μL (D) all show signs of transgene expression in the RPE layer, without visible signs of inflammation or cell toxicity. RPE retinal pigment epithelium; OS outer segments; ONL outer nuclear layer; INL inner nuclear layer.