Fenestrations and preferential flow routes in the prelaminar optic nerve through wet scanning electron microscope and perfusion of tracers.
OBJECTIVE
We study the vitreous interface of the optic disc to delimit the passages for the flow of fluids through the prelaminar tissue of porcine eyes.


METHODS
Wet scanning electron microscope (SEM), conventional SEM and transmission electron microscope (TEM) were used to explore the surface of the optic nerve of the pig. The vitreous cavity was perfused with a fluorescent marker and colloidal gold at controlled pressure. Samples of perfused optic nerve head were cryosectioned and observed with the confocal laser microscope (lectin) or resin embedded and observed under TEM (gold).


RESULTS
Fenestrations were present under the SEM in all three regions of the vitreous interface. SEM results were confirmed at the TEM level and under the wet-SEM. Perfusion experiments traced the flow of a fluorescent molecule delineating routes of preferential flow with origin in the fenestrations. Colloidal gold marked the site of entrance in the prelaminar tissue identifying major fenestrations in the basal membrane.


CONCLUSIONS
Interchange of fluid between the optic nerve and the vitreous cavity in the pig is facilitated by fenestrations of varied sizes in the basal membrane and preferential flow routes through the prelaminar tissue. Preferential flow routes exist in the extracellular spaces of Elschnig and Kuhn' astrocytes and give a sharply distinct image when compared with flow through zones in which astrocytes envelope axons. Escape routes may be instrumental in preventing oedemas of the optic nerve head, but they could also serve as entrance doors for fluids from the vitreous and aqueous and play a pathogenic role in ageing and glaucoma.
Carreras
F Javier
FJ
Department of Surgery (Ophthalmology), Faculty of Medicine, University of Granada, Granada, Spain. fjcarreras@telefonica.net
Porcel
David
D
Guerra-Tschuschke
Isabel
I
Carreras
Ignacio
I
D000818:Animals; D001253:Astrocytes; D001369:Axons; D017979:Gold Colloid / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000378:metabolism; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009898:Optic Disk / Q000378:metabolism* / Q000648:ultrastructure*; D009900:Optic Nerve / Q000378:metabolism* / Q000648:ultrastructure*; D010477:Perfusion; D013552:Swine; D014822:Vitreous Body
D017979:Gold Colloid