Normative Orbital Measurement Based on Computed Tomography Imaging in Tertiary Care Hospital, Bangalore, Karnataka

Introduction: The orbit is an anatomically complex region. Clear idea of the normal orbital measurements is needed for the diagnosis and management of the various diseases that may affect the orbit like optic neuritis, optic nerve glioma, meningioma, proptosis and exophthalmos. Aim: To evaluate normative orbital measurement at tertiary care hospital in Bangalore, Karnataka in Indian population based on Non Enhanced Computed Tomography (NECT) imaging. Materials and Methods: A cross-sectional observational study of 100 patients referred to a tertiary care centre for NECT of the brain for diseases other than those of the orbits was conducted. Patients having any orbital disorder, surgery or trauma and having metallic implants were excluded from the study. The patients of all age groups and either sex were included. The horizontal orbital diameter, vertical orbital diameter, orbital index, optic nerve complex, globe position, interorbital diameter and interzygomatic line measurements were calculated for 100 patients, i.e., total of 200 orbits using both axial and direct coronal CT images. Mean measurements of these parameters were calculated. Scans were performed on Siemens Somatom Perspective 128 slice multi- detector CT scanner. All statistical analysis was performed using Statistical Package for The Social Sciences (SPSS) for windows software (SPSS Inc. Illinois, Chicago, USA). Results: The mean orbital index was 118.6 and 118.3 for right and left orbit, respectively. It was derived from mean horizontal orbital diameter of 32.5 mm and 31.7 mm of right and left orbit, respectively and mean vertical orbital diameter of 38.4 mm and 37.4 mm of right and left orbit, respectively. Mean optic nerve sheath complex diameter was 5.2 mm and 5.4 mm for right and left orbit, respectively, while mean globe position measurements 6.7 mm and 6.8 mm of right and left orbit, respectively. Average interorbital distance was 22.9 mm and average interzygomatic distance 97.1 mm. Conclusion: The present study has given normative mean measurements for various orbital structures that are essential to ophthalmologists and radiologists to differentiate normal from abnormal dimensions which is likely to be helpful in accurate assessment of various orbital pathologies.