Is swearing by one's mother considered a harmful oath that should not be upheld, or does it require expiation, especially given that doctors have recommended a laser operation for her eye, even though she swore not to do it?

Since the doctors have recommended that your mother undergo laser surgery, it is better for her to break her oath and expiate for it, and have the surgery. This is based on the Prophet's (peace be upon him) saying: "By Allah, if Allah wills, I will not swear an oath and then see something else as better than it, except that I will expiate for my oath and do that which is better."