Can your unit tell you that you can not ride your motorcycle unless you have a doctor's note saying you can?

Yes they can tell you that you can't ride a motor cycle. But I've never heard of the doctor's note thing. Typically in order to receive permission to ride a personal motorcycle you need to meet 3 requirements.

1.) You need to pass the motorcycle basic rider's course.
2.) You need to join the unit motorcycle club and attend scheduled rides
3.) You must be wearing proper PPE at all times of operation.

Those were literally the only requirements I've seen on motorcycle riders and as you can see, it's mainly to ensure you know how to properly and safely operate one. This doctor's note thing is a weird excuse, but yes your command can tell you not to ride a motorcycle for safety reasons.

Based on vague information about a vision problem yes they can prohibit you from riding if they see it as a safety issue.

SPC (Join to see) I am going with "NO!" Unless you have something impeding your ability to ride a motorcycle, then NO...you should be able to ride it. As long as you have the proper license to ride, insurance for coverage and inspection with passing grade, there is no reason you cannot ride your bike...... Your UNIT doesn't have the right to tell you that you cannot ride your motorcycle unless it comes from the top and is applied to everyone.