Normative measurements of orbital structures on contrast enhanced computed tomography: An Australian study

Khizar Rana, Valerie Juniat, Sandy Patel, Dinesh Selva

Meeting:  2022 RANZCO


Date:      -

Session Title: FREE PAPERS – Oculoplastic/Ocular Oncology

Session Time:      -

Purpose: To determine the normal diameters of the optic nerves sheath (ONSD), extraocular muscles, and normal globe position and correlate with patient demographics in an Australian cohort.

Method: Consecutive patients who underwent contrast enhanced computed tomography orbits between 1 January 2019 to 31 March 2021 were included. Patients with bilat- eral disease or poor scan quality were excluded.

Results: A total of 127 orbits from 114 patients were included. The mean age of participants was 53 years (19-88 years) and 54 (47.4%) were male. Normal mea- surements (mean ± SD) were as follows: medial rectus 4.31 ± 0.54 mm; inferior rectus 4.30 ± 0.53 mm; latera rectus (LR) 3.43 ± 0.54 mm; superior muscle group (SMG) 4.30 ± 0.73 mm; superior oblique 2.65 ± 0.44 mm and the ONSD 5.56 ± 0.86 mm. The mean inter- zygomatic distance was 97.4 ± 4.1 mm and mean globe position was 6.8 ± 2.9 mm. The mean diameters of the SMG, LR, superior oblique, ONSD and interzygomatic distance were significantly larger in males than females (p < 0.05). Significant positive correlation was found between age and LR (r = 0.34, p < 0.01), ONSD (r = 0.24, p < 0.01) and SMG (r = 0.32, p < 0.01) diameters. Conclusion: Contrast enhanced computed tomography imaging is commonly used for evaluating orbital pathol- ogy. The normative orbital structures may vary with respect to age and gender. This data may assist in diag- nosing enlargement of the extraocular muscles and optic nerve as well as aiding in the evaluation of exophthalmos.