Occasionally the vision in the amblyopic eye does not improve despite the fact that the glasses have been worn full time and patching and / or penalisation has been carried out as instructed. When this happens the ophthalmologist will re-examine the back of the eye again to make sure that there is not a subtle abnormality of the optic nerve or retina (which might not have been apparent at the time of the initial examination), that could be the cause of the poor vision.