Can we make a returned employee go back on FMLA

I have an employee who was out under FMLA for three weeks and returned with a doctor's release. The problem however still exists and I want to know if we can require him/her to go back to the doctor and continue FMLA. It is a serious eye problem and we have no light duty available to accomodate it.
Comments
Even with full releases, most people need and deserve a reasonable adjustment period, usually a very brief one, during which they quickly get back up to full speed.