It's  not that the employer is "overruling" the doctor's orders--it's that the doctor does not actually have authority over the employer; a doctor cannot make policy or decisions for a company unless he happens to be an owner, executive, etc. of that company.That said, an employer is obligated to make "reasonable accomodations" for an employee with a disability, such as a vision coondition. However, at the same time, the employee must be able to safely do all aspects of the job, even with reasonable accomodations. So if it would be safe to wear the dark tinted safety glasses and you have a medical condition requiring them, then your employer should have to let you do this--and if they don't, you may have a legal claim for disability-based discrimination. (You could contact your state's equal/civil rights agency, or speak with an employment law attorney about a possible lawsuit.)However, if the reason for the policy change is that the employer discovered that it was unsafe to use the tinted glasses, or their insurer said they could not get coverage if employees wore other than clear safety glasses, or regulations governing your industry now require clear glasses, then the employer does not have to let you wear them, regardless of your condition or prescription. An employer is not obligated to incur a safety or liabilty risk, to give up insurance coverage, or to violate the law to accomodate an employee. So if there is a safety, legal, or insurance reason behind the policy change, the employer can most likely deny you the right to use the tinted glasses, even if that means you can't then do your job and would be terminated.