Histochemical localisation of mitochondrial enzyme activity in human opticnerve and retina

Aims-To demonstrate the quantitative distribution of mitochondrial enzymes within the human optic nerve and retina in relation to the pathogenesis of ophthalmic disease. Methods-Enucleations were performed at the time of multiple organ donation and the optic nerve and peripapillary retina immediately excised en bloc an d frozen. Reactivities of the mitochondrial enzymes cytochrome c oxidase an d succinate dehydrogenase were demonstrated in serial cryostat sections usi ng specific histochemical assays. Results-In the optic nerve the unmyelinated prelaminar and laminar regions were rich in both cytochrome c oxidase and succinate dehydrogenase. Myelina tion of fibres as they exited the lamina cribrosa was associated with an ab rupt reduction in enzyme activity. Within the retina, high levels of enzyme activity were found localised within the retinal ganglion cells and nerve fibre layer, the outer plexiform layer, inner segments of photoreceptors, a nd the retinal pigment epithelium. Conclusions-Mitochondrial enzyme activity is preserved in human optic nerve and retina retrieved at the time of multiple organ donation. The distribut ion of enzyme activity within the eye has implications for the understandin g of the pattern of ophthalmic involvement seen in mitochondrial diseases a nd the site of ganglion cell dysfunction in those patients with optic nerve involvement.