Relative post-mortem sparing of afferent pupil fibers in a patient with 3460 Leber's hereditary optic neuropathy.

BACKGROUND: Relative sparing of the pupillary reflexes in patients with leber's hereditary optic neuropathy (LHON) has been observed clinically. This study sought to test histologically whether retino-pupillary fibers are spared in LHON.
METHODS: Di-I, a fluorescein dye that allows anterograde labeling of axons, was injected into the brachium of the superior colliculus in post-mortem brain from a patient diagnosed with LHON (3460 mutation) and a normal control brain. After 4 weeks, serial fragmatome sections were obtained in the pretectal area and further stained with propidium iodide (PI stains DNA) to delineate the pretectal nuclei in the dorsal midbrain. Examination was performed under a confocal microscope. Optic nerves obtained from the above subjects were cut, mounted and stained with p-phenylenediamine (PPD) and trichrome stain for digital morphometry.
RESULTS: Di-I-labeled fibers were visible on all sections from the superior colliculus to the pretectum in the LHON and the control specimens, as were the nuclei in the cell bodies stained with PI. There was mild attenuation of the afferent pretectal fibers in LHON, but this was not as dramatic as the attenuation of the total population of fibers in the LHON optic nerve.
CONCLUSIONS: In our LHON patient, the preservation of retinofugal fibers to the pretectum lends support to the clinical observation of relatively preserved pupillary function in LHON.