Effects of intraocular pressure and cerebrospinal fluid pressure modulation on optic nerve head topography

Purpose. To measure the effects of intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFP) modulation on optic nerve head topography. Methods. In this pilot study, two dogs of varying breed mixture were used. We controlled IOP by inserting two 25-gauge cannulae (one attached to a pressure transducer and the other to a hydrostatic pressure head) into the anterior chamber. CSFP was controlled similarly by inserting two 18-gauge needles into the lateral ventricle. First IOP was raised from 20 to 32 mm Hg in steps of 3 mm Hg, keeping CSFP constant at 0 mm Hg. Next CSFP was raised from 0 to 12 mm Hg in steps of 3 mm Hg, keeping IOP constant at 17 mm Hg. Finally both IOP and CSFP were raised concomitantly from 17 mm Hg and 0 mm Hg to 32 mm Hg and 12 mm Hg respectively. We used a Heidelberg Retina Tomograph to image the optic nerve head and peripapillary retina through a plano corneal contact lens. A set of six high-quality scans were obtained at each pressure setting using a 10 degree scan angle. Results. Successive IOP increase (with constant CSFP) produced a successive backward movement of the optic nerve head in the range of 20-120 microns, though the movement in one animal was not homogenous. Successive changes in CSFP (with constant IOP) produced significant forward movement of the optic nerve head with large changes (> 100 microns) observed even with a CSFP change from 0 to 3 mm Hg. Concomitant changes in IOP and CSFP produced relatively little change. Conclusions. IOP and particularly CSFP changes have a significant effect on optic nerve head topography. Concomitant IOP and CSFP change (which keeps the translaminar pressure difference constant) has a smaller effect.