Morphometric characteristics of the optic canal and the optic nerve

Abstract

The optic nerve (ON), a major component of the visual system, is divided into four segments: the intrabulbar (IB), the intraorbital (IO), the intracanalicular (ICn) and the intracranial (ICr). The ICr ends with the two nerves partially decussating in the optic chiasm (OCh). The purpose of this study is to provide a detailed description of the dimensions of the OC (the diameter and the surface area of its foramina and the central segment, as well as the length of the OC and the thickness of its walls) as well as the ON (the length of the ON segments, the diameter of the ICn segment of the ON, the angle of decussation in the OCh, as well as the distance between the two ON at the cranial foramen of the OC). The acquired data was then used to estimate the volume of the OC and the ICn segment of the ON. The morphometric research was performed on 25 cadavers (17 male and 8 female) and 30 skulls. The surface area of the central segment of the OC was significantly smaller than the cranial foramen (p = 0.02) and the orbital foramen (p = 0.009). The inferior wall of the OC was significantly shorter than the other OC walls (p < 0.0001). The IO segment of the ON was the longest, where the difference to the ICn and ICr was statistically significant (p < 0.0001). The surface area of the ON at the cranial foramen was significantly larger than the surface area at the central segment of the OC (p = 0.02) and orbital foramen (p < 0.0001). The difference between the surface areas of the ON at the orbital foramen and the central segment of the OC was also statistically significant (p = 0.01).The estimated volume of the OC was calculated to be 190.72 mm³, and the volume of the ICn segment of the ON was estimated to be 50.25 mm³. It is absolutely crucial to open the central segment of the OC when decompressing the ON, due to the narrowing of the OC in this segment.

Evaluation of the Cranial Aperture of the Optic Canal on Cone-Beam Computed Tomography Images and its Clinical Implications for the Transcranial Approaches

“…In this study, a significant difference was not found between right and left diameter measurements, similar to most studies in the literature. 22,23,34,36–38 However, Kumar et al 1 observed that the right aperture height (5.14 ± 0.73 mm) was greater compared to the left (4.82 ± 0.77 mm). Moreover, Kalthur et al 41 found that the right aperture diameters (height: 3.67 ± 0.82 mm, width: 4.68 ± 0.86 mm) was greater compared to the left (height: 3.54 ± 0.71 mm, width: 4.51 ± 0.79 mm).…”

“…lww.com/SCS/D892) (mean data range for the aperture height: 3.60-5.17 mm, and for the aperture width: 4.59-7.38 mm). 1,22,[31][32][33][34][35][36][37][38][39][40][41] Prado et al 36 measured the aperture diameter in fetuses (right: 3.76 mm, left: 3.79 mm), children (right: 4.67 mm, left: 4.72 mm), and adults (right: 5.24 mm, left: 5.43 mm), and declared that the width increased from fetal period to adult period. In addition, Ten et al 22 measured the aperture diameters (width: 6.12 ± 0.84 mm, height: 4.35 ± 0.64 mm) in pediatric subjects aged between 1 and 20 years, and observed that its diameters did not alter from the prepubescent period.…”

Long-Term Visual Prognosis in Patients With Aquaporin-4-Immunoglobulin G–Positive Neuromyelitis Optica Spectrum Disorder

“…It means that the longer extent was correlated with the involvement of intracanalicular optic nerve. Intracanalicular optic nerves are surrounded by bony structures; even a small amount of swelling of the tissue may cause optic nerve compression because of vulnerability to compression, owing to space limitations in the canal (23,24). Therefore, further studies should be needed to certify the effect of lengths and location of lesions, separately.…”

Length of orbital margins of dry skulls in a local Pakistani population

“…It is therefore important to consider the lengths of the superior and inferior orbital depths during deep orbit surgical operations in order not to damage the optic nerve and associated vessels (Huanmanop et al;2007). The aim of study was to collect data of bony orbits from our local population because racial differences exist as shown by previous studies (Yoon et al;2016) and (Radunovic M et al;2018). As we lack data from our region in Pakistan, this study will be helpful in various techniques of anesthesia and in maxillofacial, orbital and plastic surgical procedures to reduce the risk of various complications…”