Average Diameter of Fibrous Bundles Connecting the Optic Nerve to the Optic Sheath Decreases with Increased Intracranial Pressure

Objective The objective of this study was to evaluate the effect of increased intracranial pressure (ICP) on the fiber bundles connecting the optic nerve to the optic sheath in a swine model. Methods Increased ICP was induced in an anesthetized swine model by passing a catheter through a drilled opening into the epidural space. ICP was monitored continuously. Post euthanasia and enucleation of the swine eyes, a section of optic nerve sheath, with the intact nerve, was removed from both the control and experimental swine model. The tissue was fixed overnight in paraformaldehyde and glutaraldehyde in a sodium cacodylate buffer, postfixed in osmium tetroxide in a sodium cacodylate buffer, dehydrated with a graded ethanol series, and critical point dried with carbon dioxide. The dried control and experimental model sections were mounted and imaged using a scanning electron microscope (SEM). Images of the trabecular meshwork were taken radially around the optic nerve at several magnifications. The images were segmented and analyzed using the ImageJ plug‐in DiameterJ. Segmentation quality was confirmed using image subtraction of the original image from the segmented image and vice versa. All images had false positive and false negative total percentages of less than 5% of all pixels. Image overlays of the segmented and original images confirmed this qualitatively. Results Mean and median fiber bundle diameters were recorded for a total of 61 images. 30 (49.1%) of the images analyzed were from the control sample and 31 (50.9%) were from the experimental sample. An analysis of variance found that both the mean (.52 μm) and median (.62 μm) fibrous bundle diameters were significantly different (smaller) for the experimental model as compared to the control (.73 μm and .85 μm) respectively (p<.0001). The relationship between mean and median fibrous bundle diameters and sample (control or experimental) was not significantly correlated to radial location (relative to the optic nerve) or magnification of the image based on analyses of covariance. Conclusion This research demonstrates that in a swine model the fibrous bundles of the optic sheath's connections to the optic nerve are statistically different (smaller) after exposure to increased ICP. Future research will evaluate if the thinning is caused by increased ICP, by increasing the sample size and using other methods to induce increased ICP. Future research may impact the current understanding of traumatic brain injury. Support or Funding Information Medical Scholars Program, Medical College of Georgia at Augusta University, Summer 2017 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .