The only moving parts on an optical mouse are the buttons and scroll-wheel so I doubt it's wear and tear causing the problem. Still, it is subject to faults occuring just like everything else. An internal fault may be causing the mis-tracking.
Try to borrow a fault-free mouse and if that works okay buy yourself a new one.
I've already tried a different mouse and it has worked perfectly. I did consider an internal problem in which case I will have to swap mice.
Try and cleaning the eye.
Take a cotton swab with some alcohol and wipe where the eye is on the bottom of the mouse.
If it wireless then try the battery.
I'll give your advice a shot. I was unsure how I should go about cleaning this mouse and wasn't game to try without advice first. As it's corded I won't have a battery to replace. If this doesn't work I suppose I will have to get rid of it?