Re: Left eye vision disorder, cannot explain properly.
Adam, it sounds like you have a scotoma, a technical term for a blind spot in your vision. That's probably why you're clipping the curb - you don't see it.
Have you been examined by an ophthalmologist? I doubt an optician can properly diagnose the cause - they just fit glasses.
You ought to be checked out by an eye doctor to see if the cause can be determined. It may not be reversible but if you know the cause it may help prevent further vision loss.
Best of luck!