One of Spike's eyes is cybernetic.
The one organic eye he has he probably feels more connected to and when he sees things out of it he's reminded of all the shit he's done the people he's killed and the lives he's ruined in his wake. The cybernetic eye meanwhile is just a machine, it lets him see things but only as they objectively are. There's no 'memories' no 'echoes' with his cybernetic eye.
As such he's caught between 'seeing' things as they are and 'seeing' things for what they represent about his past at the same time. Or something.