THE INFLUENCE OF CEREBROSPINAL-FLUID PRESSURE ON THE LAMINA-CRIBROSA TISSUE PRESSURE-GRADIENT

Purpose. To measure the tissue pressure gradient through the optic dis k and to determine the relationship between intraocular, cerebrospinal fluid, and retrolaminar tissue pressures. The relationship of optic n erve subarachnoid space pressure to intracranial cerebrospinal fluid p ressure also was explored. Methods. Micropipettes coupled to a pressur e transducer were passed through pars plana and vitreous to enter the optic disk in the anesthetized dog. Using a micromanipulator, pipettes penetrated the optic disk in steps while pressure measurements were t aken. In some animals, pipettes also were passed into the optic nerve subarachnoid space. Lateral ventricle cerebrospinal fluid pressure, in traocular pressure, and arterial blood pressure were measured concurre ntly, and the effect of raising CSF pressure was explored. Results. Re trolaminar tissue pressure was largely dependent on the surrounding ce rebrospinal fluid pressure, which was on average 8.6 +/- 3.5 mm Hg (SD , n = 8) higher, and was independent of intraocular pressure. Most (85 % +/- 15% [SD, n = 8]) of the pressure drop between intraocular pressu re and retrolaminar pressure occurred across the anterior 400 mu m of disk tissue. When the intraocular pressure was 21 mm Hg and the cerebr ospinal fluid pressure was zero, retrolaminar tissue pressure averaged 7 mm Hg and the translaminar pressure gradient was 3.08 +/- 0.29 mm H g/100 mu m tissue (SD, n = 3). Optic nerve subarachnoid spate pressure was equivalent to lateral ventricular pressure. Conclusions. These re sults show that cerebrospinal fluid pressure largely determines retrol aminar tissue pressure; hence, along with intraocular pressure, it is of major importance in setting the translaminar tissue pressure gradie nt. Results also demonstrate hydrostatic continuity between the optic nerve subarachnoid space and the lateral ventricle. That the translami nar pressure gradient can vary independently of intraocular pressure m ay be of importance in understanding the pathophysiology of glaucoma.