Did you export his eyeball with "include existing groups in polygon groups" checked? If not, do that. Just go to File>Export as OBJ> Select Don's right or left Eye and nothing else. Make sure "include existing groups in polygon groups" is checked in the export options dialogue box.

When you reimport the new OBJ it will be completely white but you can either copy the materials over from Don one by one or if you have any Eye MATs or MC6 materials for just his eyes, they will load up now.