| Purpose Previous investigations have suggested that low intracranial pressure (ICP), which increased the trans-lamina cribrosa pressure difference (TLCPD), may play an important role in the pathogenesis of Normal Tension Glaucoma (NTG). However, the relationship between ICP measured by lumbar puncture and the cerebrospinal fluid pressure (CSFP) around the optic nerve is still in vague. Since no direct measurement of local CSFP around optic nerve can be performed to date intravitally on human. We proposed measuring of the Optic Nerve Sheath Diameter (ONSD) and Optic Nerve Diameter (OND) by 3.0-Tesla MRI as a substitute to evaluate the local CSFP around optic nerve in patients diagnosed POAG.
Methods 27 POAG patients, in whom 13 NTG patients and 14 high IOP patients (HPG group) and 16 subjects without eye diseases served as control were enrolled in this study. ONSD and OND were determined at 3mm, 9mm, and 15mm behind the eye ball with T2-weighted fast recovery fast spin echo (FRFSE) fat suppressed sequence in 3.0-Tesla MRI providing a spatial resolution of 0.16mm. An ANOVA with post-hoc LSD multiple comparisons were used to analyze the data among the three groups. A P<0.05 was required for results to be considered statistically significant.
Results At 3mm behind the eye ball, there has no significant difference of OND among three groups; but the ONSD of NTG group is significantly narrower than control group (p<0.05). At 9mm, the OND of HPG group is significantly narrower than the other two groups (P<0.05); For ONSD at 9mm, the NTG group and HPG group are both significantly narrower than the control group (P<0.05). At 15mm, the OND of NTG group and HPG group are both significantly narrower than the control group (P<0.05); For ONSD at 15mm, the NTG group and HPG group are both significantly narrower than the control group (P<0.05).
Conclusions This study directly shows that in Normal Tension Glaucoma patients the ONSD is narrow, which correspond well with our previous work and suggest that the local CSFP around ON in NTG patients is low and lead to an elevated TLCPD. The optic nerve diameter of open angle glaucoma patients is shrunk along with the optic nerve length and this shrinkage also retracts the optic nerve sheath, which may further block the CSF circulation between the subarachnoid space of optic nerve and brain at the further site of the optic nerve length behind the eye ball and may lead to a more elevated TLCPD in a long term manner. |
