BackgroundOptical nerve damage of glaucomatous eyes is associated with intracranial pressure.Conventional method of evaluating intracranial pressure is to measure cerebrospinal pressure by lumber puncture.However, the measurement of intraorbital optical nerve parameters, a novel method of evaluating intracranial pressure, is introduced in this field.

ObjectiveThis study was to measure and analyze the intraorbital optic nerve sheath diameter (ONSD) and cross sectional area (ONSA) in normal population using multi-slice spiral CT.

MethodsThis study protocol was approved by Clinical Ethic Committee of Shenzhen Chinese Traditional Medical Hospital and followed Hersinki Declaration.Informed consent was obtained from each individual prior to any medical examination.One hundred and five eyes of 105 normal persons with normal cerebral CT image were enrolled in Shenzhen Chinese Traditional Medical Hospital from January 2012 to September 2013.Cerebral volume was scanned in all the individuals by 64 slice spiral CT.The brain images were obtained for the curve planar rebuilding of intraorbital optical nerve on image post-processing workstation.The maximum and minimum of ONSD and the ONSA in axial sections at 3, 6, 9, 12 and 15 mm far away from globe wall were measured using a standardized technique to analyze the change of optical nerve parameters at different point locations.These parameters were compared in different gender or eyes.The correlation among age and the optical nerve parameters at 3 mm far away from globe wall was evaluated by multivariate regression analysis.

ResultsThe average maximal ONSDs were (6.24±0.47), (5.56±0.44), (5.18±0.43), (4.82±0.41) and (4.69±0.41) mm; the average minimal ONSDs were (5.56±0.50), (4.97±0.41), (4.55±0.35), (4.26±0.39) and (4.10±0.40) mm; the average ONSAs were (27.68±4.40), (22.02±3.35), (18.74± 2.75), (16.34±2.72), (15.40±2.68) mm ² at 3, 6, 9, 12 and 15 mm far away from posterior eyeball wall, respectively, showing significant differences in the maximal/minimal ONSDs and ONSAs among the different point locations ( F=218.329, 215.906, 246.924, all at P=0.001). No significant differences were found in the maximal/minimal ONSDs and ONSAs between male and female or between the right eyes and left eyes (gender: t=1.805, P=0.074; t=1.930, P=0.056; t=1.329, P=0.187; eyes: t=0.724, P=0.471; t=1.562, P=0.121; t=1.424, P=0.158). No significant correlations were seen between age and maximal/minimal ONSDs or ONSAs with the coefficients of 1.873, 7.415 and -0.853 correspondingly ( P=0.847, 0.460, 0.637).

ConclusionsIntraorbital section of optical nerve can be rebuilt using standardized technique after scanning of 64 slice spiral CT.The cross section of intraorbital optic nerve sheath is oval in shape and the optic nerve is thinning with the increase of distance far away posterior eyeball wall in normal populatuion.