The red dot is an internal reflection caused by the deer's intense eyeshine bouncing around between the CMOS sensor and the back of the lens. It's not a defect, just simple physics. It can be mitigated somewhat by setting your camera high and pointing down or setting low and pointing up, but it's a fool's errand to even try since we can't control how high a deer holds its head while posing for the camera. It's best to just accept it and live with it or, if you feel compelled, to clone
the reflection out.