Isolated iridoplegia or internal ophthalmoplegia may be due to impairment of the effector muscles in the eye, defective parasympathetic innervation, or the presence of atropinic substances in the eye. Pharmacologic blockade can be identified by the pupil's failure to constrict to pilocarpine drops. Because of its clarity and technical simplicity, this test should be in general use as an office procedure.
Thompson HS, Newsome DA, Loewenfeld IE. The Fixed Dilated PupilSudden Iridoplegia or Mydriatic Drops? A Simple Diagnostic Test. Arch Ophthalmol. 1971;86(1):21-27. doi:10.1001/archopht.1971.01000010023006