Microvessels of the human optic nerve head: ultrastructural and radioreceptorial changes in eyes with increased IOP.

BACKGROUND: Ultrastructural, morphological modifications in the microvessels of the optic nerve head were studied in human eyes with normal intraocular pressure (IOP), with slightly increased IOP, and with strongly increased IOP. Moreover, the distribution of beta-adrenergic receptors was analyzed in the same samples. METHODS: Six enucleated human eyes were studied. Small pieces of the optic nerve head and of iridocorneal angle (including trabecular meshwork) were dissected immediately after autopsy. The sections were studied with transmission electron microscopy and autoradiography. Radiolabelled pindolol was used to locate beta-adrenergic receptors topographically on fresh sections of human eye. RESULTS: Transmission electron microscopy demonstrated that elevated IOP induces ultrastructural modifications of the microvessels of the optic nerve head. Autoradiographic experiments showed the presence and distribution of beta-adrenergic receptors in the optic nerve head of eyes with both normal and increased IOP. INTERPRETATION: Increased IOP initially compresses the microvessels of the optic nerve head. The number of beta-adrenergic receptors increased markedly in the eyes with raised IOP. Further studies are needed to clarify the physiological and pathological roles of these receptors