Purpose.  To assess the orbital cerebrospinal fluid pressure (CSF-P) in ocular hypertensive (OHT) patients with elevated intraocular pressure (IOP) but without development of glaucomatous optic nerve damage, the orbital subarachnoid space width (SASW), as surrogate for the local CSFP around orbital, was determined by 3.0-Tesla MRI in OHT patients and normal controls.
Methods.  The prospective observational study included 12 individuals with ocular hypertension, in which group the IOP was corrected for its dependence on central corneal thickness (IOP corrected), and 22 normal controls. With magnetic resonance imaging with fat suppressed fast recovery fast spin echo (FRFSE) T2-weighted sequences, we measured the optic nerve sheath diameter (ONSD) and optic nerve diameter (OND) at 3 mm, 9 mm and 15 mm posterior to the globe. ONSD minus OND equals orbital SASW.  
Results.  There was no statistically difference in retinal nerve fiber layer thickness measured by Optical Coherence Tomography (P=0.5) between OHT group(105±11μm) and the control group (109±10μm). At all three measurement locations of 3mm, 9mm and 15mm, the orbital SASW was significantly (P<0.05, P<0.01, and P<0.01, respectively) wider in the OHT group than control group. As for ONSD, the ocular hypertension group and the control group did not vary significantly at 3mm, 9mm and 15mm (P=0.165;P=0.448; and P=0.153, respectively). As well as ONSD, OND of the OHT group was
not statistically different from that of the control group at all the measurement locations (P=0.799; P=0.542; and P=0.970, respectively).
Conclusions.  The wider orbital subarachnoid space in OHT individuals as compared with controls suggests a higher
orbital cerebrospinal fluid pressure in OHT individuals. We postulate that the elevated orbital CSF-P delayed or prevented the onset of glaucomatous orbital damage by compensating for an increased IOP and reducing trans-laminar pressure difference in the eyes with elevated IOP.