Nerve degeneration in irises and notably wider pupils in response to light of dt/dt mice. Wholemount preparations of irises were stained by immunofluorescence for pan neuronal marker PGP 9.5 (A and B). In wild-type mice, PGP 9.5-positive fibers were circumferentially distributed along the pupillary ruff in the sphincter pupillae (SP) area and were radially oriented toward the pupil in the dilator pupillae (DP) area (A). Compared with intact wild-type mice, a few remaining immunopositive fibers exhibited marked decrease in density throughout the sphincter and dilator area in dt/dt mice (B). Ciliary ganglion (CG) and short ciliary nerve (SCN) could be found along the outer surface of the optic nerve (ON) in wild-type mice (C). However, the smaller nerve bundle (arrow) and ganglion (arrowhead) could be observed in dt/dt mice (D). High-power photomicrographs revealed that the ganglion with typical neuronal morphology was observed in wild-type mice (E), whereas the ganglion with fewer number and smaller size of neurons could be found in dt/dt mice (F). To investigate the denervation effect in the iris of dt/dt mice, the light-induced pupillary reflex was tested. The pupillary diameter was narrower in wild-type mice during the pupillary reflex test (G), whereas the pupil was notably wider and iris constriction was weaker in response to light in dt/dt mice (H). Scale bars = 200 μm in A-F; 2 mm in G and H.