PDE5 Inhibitors (the blue pill) can end up crossing the blood brain barrier in your body as well as the blood retinal barrier. When it does this, it actually can end up inhibiting something we call PDE6. PDE6 is important when it comes to us processing visual signals and seeing normally. When PDE5 crosses that blood retinal barrier and inhibits the PDE6, you start to notice problems with your eyesight. This is ultimately why some of the reported side effects when taking the blue pill are visual