1 SUBMITTED 9 NOV 21 1 REVISIONS REQ. 18 JAN 22; REVISIONS RECD. 27 JAN 22 2 ACCEPTED 27 FEB 22 3 ONLINE-FIRST: MARCH 2022 4 DOI: https://doi.org/10.18295/squmj.3.2022.023 5 6 Radiologic Assessment of Orbital Dimensions among Omani Subjects 7 Computed tomography Imaging-based study at a single tertiary center 8 Eiman Al Ajmi,1 Marwa Al Subhi,4 Mallak Al Maamari,2 Humoud Al 9 Dhuhli,1 *Srinivasa R. Sirasanagandla3 10 11 Departments of 1Radiology & Molecular Imaging and 3Human & Clinical Anatomy, 2College 12 of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Oman; 4Radiology 13 Residency Program, Oman Medical Specialty Board, Muscat, Oman. 14 *Corresponding Author’s e-mail: srinivasa@squ.edu.om 15 16 Abstract 17 Objectives: A sound knowledge of the normal orbital dimensions is clinically essential for 18 successful surgical outcomes. Racial, ethnic, and regional variations in the orbital dimensions 19 have been reported. This study aimed to determine the orbital dimensions of Omani subjects 20 who had been referred for computed tomography (CT) images at a tertiary care hospital. 21 Methods: A total of 273 Omani patients referred for a CT scan of the brain were evaluated 22 retrospectively, using electronic medical records database. The orbital dimensions were 23 recorded using both axial and sagittal planes of CT images. Results: The mean orbital index 24 (OI) was found to be 83.25±4.83, and the prevalent orbital type was categorized as 25 mesoseme. The mean orbital index was 83.34±5.05 and 83.16±4.57 in males and females, 26 respectively, with their difference being statistically not significant (p=0.76). A statistically 27 significant association was observed between the right and left orbits regarding horizontal 28 distance (p<0.05) and vertical distance (p<0.01) of orbit and OI (p<0.05). No significant 29 difference between the OI and age groups was observed in males and females. The mean 30 interorbital distance and interzygomatic distance were found to be 19.45±1.52 mm and 31 95.59±4.08 mm, respectively. These parameters were significantly higher in males (p<0.05). 32 Conclusions: Results of the present study provide reference values of orbital dimensions in 33 mailto:srinivasa@squ.edu.om 2 Omani subjects. The prevalent orbital type of Omani subjects is mesoseme, which is a 34 hallmark of the white race. 35 Keywords: Computed Tomography, Ethnicity, Orbit, Oman, Variation, Hypertelorism. 36 37 Advances in Knowledge 38  This is the first study to evaluate the orbital dimensions of the Omani population. 39  Results of the present study provide reference values of orbital dimensions in Omani 40  subjects. 41  The prevalent orbital type of Omani subjects is mesoseme, a hallmark of the white race. 42 43 Application to Patient Care 44 1.The reference values of orbital dimensions including orbital index, interorbital distance 45 and interzygomatic distance reported in this study are essential for diagnosing and treating 46 various orbital pathologies. 47 2.These values are also crucial for surgical corrections of craniofacial anomalies such as 48 orbital hypertelorism, hypotelorism, and orbital clefts. 49 50 Introduction 51 The bony orbit or orbital cavity is a complex anatomical region of the facial skeleton. The 52 orbit and its contents are affected by various diseases1 and craniofacial anomalies such as 53 orbital hypertelorism, hypotelorism, and orbital clefts.2,3 The majority of orbital diseases and 54 craniofacial anomalies require a thorough knowledge of the normal orbital dimensions to 55 diagnose and treat them effectively. Previously, many studies have enumerated the reference 56 values of orbital dimensions among different populations.1,4,5 These studies reported a 57 significant variation in orbital dimensions depending on the race and ethnicity of the 58 population. Generally, the orbit shape differs according to ancestry: rectangular orbits are 59 present in Africans, angular orbits in northern and southern Europeans, and round orbits in 60 Central Asians and Central Europeans.6 In most circumstances, the breadth of the orbital 61 cavity is greater than the height, and the orbital index (OI) reflects this relationship. Paul 62 Broca has developed OI to quantitatively enumerate the orbit size and symmetry for the first 63 time.5 OI refers to the proportion of orbital height to the orbital width multiplied by 100%. 64 The shape of the face determines the OI of an individual.4 Based on different values obtained 65 from previous research, OI is classified into three categories. The first category is megaseme, 66 3 which refers to a large index and is seen in yellow races. The second category is mesoseme, 67 which indicates intermediate value and is associated with the white races. And the small one, 68 microseme, is a characteristic of the black races.7 69 70 Craniofacial indices are a reliable source to provide successful results for ethnicity 71 identification compared to appendicular skeletal remains indices.8 Radiological investigations 72 are frequently used for craniofacial indices where the dry bone collection is impossible.9 73 Factors such as gender, age and laterality influences on OI have been reported in the majority 74 of the studied populations.10-12 The interorbital distance (IOD) is typically used as diagnostic 75 criteria in evaluating craniofacial anomalies such as hypertelorism, hypotelorism, and orbital 76 clefts.2,3,13 This parameter is also used to determine the severity of these anomalies and while 77 planning the surgical correction.14,15 In addition to the clinical importance, orbital dimensions 78 are frequently used in anthropology and forensic medicine.11 Till date, there are no studies to 79 evaluate the orbital dimensions of the Omani population. Hence, in the present study, we 80 sought to provide the baseline data of OI and IOD of Omani subjects referred for CT scans at 81 a tertiary care hospital and classify them under one of the three predetermined categories. 82 83 Materials and methods 84 In the present study, the adult Omani patients (aged ≥18 years) who had visited tertiary care 85 referral center in the Department of Radiology and Molecular Imaging in Oman were studied 86 retrospectively using an electronic medical records database (TrakCare Unified Health 87 Information System). The study was conducted after receiving ethical approval from the 88 Medical Research Ethics Committee. Thank you for the comments. In the present study, we 89 included all the consecutive patients of either sex aged ≥18 years who had been referred for a 90 CT scan of the brain during the period from 1st January 2019 to 31st March 2019. After 91 applying the inclusion and exclusion criteria there were 273 Omani patients. This statement 92 has been added in the methods section. The patients with orbital fractures and ocular or facial 93 surgery or deformity were excluded. In addition, scans with motion artifacts or incomplete 94 coverage of the orbits and those performed for non-Omani patients were excluded as well 95 from the study sample. 96 97 All the CT scans were performed as per the routine standard protocol for non-enhanced CT of 98 the brain using 64 slice multidetector CT (Siemens Sensation 64) with kilovoltage peak of 99 120 kV and tube current modulation. The images and measurements were assessed using the 100 4 Picture Achieving and Communication System (PACS) (Synapse PACS, FUJIFILM 101 Worldwide, version 5.7.102). 102 103 The measurements were performed using the reconstructed thin slices of 1.2 mm in the bone 104 window. A window width/window level of 2000/500 was used while screening the images. 105 The following measurements were performed for every subject: the inter-orbital distance, 106 inter-zygomatic distance, horizontal orbital diameter and vertical orbital diameter. First, the 107 orientation of the axial images was adjusted to Frankfort horizontal plane which is defined as 108 the line from the highest point of the opening of the external auditory canal to the lower 109 margin of the orbital rim.16 After adjusting the axial plane, the IOD was measured as the 110 minimal distance between the medial orbital walls (Figure 1). The interzygomatic distance 111 (IZD) was determined as the maximum distance between the anterior aspects of the 112 zygomatic arches (Figure 1). The horizontal distance of orbit (HDO) for each orbit was 113 measured as the maximum distance from the anterior lacrimal crest to the lateral orbital wall 114 (Figure 2a). The vertical distance of orbit (VDO) was performed in the sagittal plane after 115 adjusting the angulation of the sagittal image along the long axis of the orbit and measured as 116 the maximum distance between the frontal and the maxillary bones (Figure 2b). Finally, OI 117 was calculated using the following formula: OI = VDO/HDO*100. 118 119 Statistical Package for the Social Sciences (SPSS, version 23.0, IBM Corporation, NY, USA) 120 for Windows was used to analyze the data. The data were presented as mean and standard 121 deviation. Independent sample t-test was used to determine the associations between the 122 orbital dimensions and gender, while paired t-test was used to determine the laterality 123 difference. The association between the orbital dimensions and age groups were determined 124 using One-way ANOVA. The differences were considered significant at p-value <0.05. 125 126 Results 127 In the present study, we evaluated 546 orbits from 273 patients. Among these patients, males 128 were 136 (49.82%), and females were 137 (50.18%). The mean age of the study subjects was 129 58.81 years ± 19.41, with a range of 18 to 94 years. Only one observer was involved in 130 screening all the 273 subjects’ CT scans to measure the orbital dimensions. The mean HDO 131 of the right and left orbits was 39.76±1.75 mm and 39.42±1.66 mm, respectively. The mean 132 VDO of the right and left orbits was 32.83±1.90 mm and 33.01±1.89 mm, respectively. 133 134 5 As described in the methods, the OI was calculated using the VDO and HDO. The mean OI 135 of the right side and left side orbits were found to be 82.67±5.36 mm and 83.83±4.93 mm, 136 respectively. A statistically significant association was observed between the right and left 137 orbits with regard to HDO (p<0.05) and VDO (p<0.01) and OI (p<0.05) (Table 1). The 138 associations of orbital dimensions with respect to gender are presented in Table 2. There was 139 no significant association between gender and OI of both sides of the orbit. The OI in 140 different age groups of female and male patients is presented in Table 3 & 4, respectively. 141 There was no significant association between age groups and IO among the study subjects. 142 The mean IOD and the mean IZD distance were found to be 19.45±1.52 mm and 95.59±4.08 143 mm, respectively. The mean IOD (p<0.05) and the mean IZD (p<0.05) were significantly 144 higher in males when compared to females. 145 146 Discussion 147 In the past, several radiological and anatomical studies have been conducted to explore the 148 bony dimensions of the orbit. Evidence from these studies reported a significant variation 149 among different races, ethnicities, and within the region. The reporting of reference values of 150 orbit dimensions is clinically important for a better diagnosis, surgical approach and outcome, 151 and follow-up of various orbital pathologies. The knowledge of orbit dimensions pertaining 152 to each race and ethnic group is also crucial in anthropology and forensic medicine, 153 particularly for identifying and classifying the skull. Despite having tremendous importance, 154 the normative bony dimensions of the orbit were not studied in all populations world-wide. 155 To date, the OI has been documented only in three populations from the Middle Eastern 156 region, including Egypt,17 Turkish18 and Iranian19 populations. To the best of our knowledge, 157 for the first time, we report the baseline data of orbit dimensions, including OI, IOD, and IZD 158 in the Omani population. 159 160 The orbital cavity possesses greater height than width and is typically classified into three 161 categories: microseme, mesoseme, and megaseme. Previously, studies from different Asian 162 countries, including Japan, China, India, Sri Lanka, Turkey and Iran, have documented the OI 163 of their respective populations and classified them under one of the categories.1,4,5 In the 164 present study, the mean OI of Omani subjects was found to be 83.25±4.83, and the prevalent 165 orbital type was categorized as mesoseme. Similar to the present study, the mesoseme orbital 166 class was found in the Iranian population. In Egyptian female subjects, it was mesoseme 167 6 while it was microseme in male subjects. In the Turkish population from the middle-eastern 168 region, the megaseme orbital category was observed.18 169 170 In the literature, there are conflicting reports on the sexual dimorphism of OI. In Omani 171 subjects, the observed OI of males was 83.34±5.05, while it was 83.16±4.57 in females. Both 172 genders belonged to the mesoseme category. No significant gender difference in OI was 173 observed in the Omani subjects. Similar findings were reported in Brazillian5 and South 174 Indian subjects20, and in Kalabaris and Ikwerres of the Rivers ethnic group of Nigeria.21 In 175 contrast, a significant gender difference in OI was found in the Igbo and Urhobos ethnic 176 groups of Nigeria and Ghanaian subjects.4 In agreement with these studies, gender 177 differences in bony volume and dimensions were observed even in the Iranian population.19 178 179 Furthermore, in Omani subjects, the laterality differences with HDO, VDO and OI were 180 statistically significant. These findings are similar to the study results from the Iranian 181 population.19 However, contradictory findings of laterality differences were observed in 182 Indian,20 Nigerian22 and Ghanaian4 populations. In the present study, there were no 183 significant differences in OI among different age groups in both males and females. Similar 184 findings were observed in Ghanaian subjects.4 However, in the Malawian7 and Igbo ethnic 185 groups of Nigerian subjects,22 the OI was significantly different in different age groups. 186 These discrepancies observed between the studies with regard to orbital dimensions and their 187 associated factors are possibly due to genetic factors. 188 189 The IOD is clinically used to diagnose both orbital hypotelorism and hypertelorism. Orbital 190 hypertelorism is distinguished by a longer IOD, most often associated with a variety of 191 craniofacial conditions, including Crouzon syndrome, craniofacial dysplasias and clefts.23 On 192 the other hand, hypotelorism is also linked to several diseases, including holoprosencephaly 193 and craniosynostosis.24 Reference values are also important while correcting the surgeries 194 involving the above-mentioned craniofacial anomalies. Previously, authors have provided the 195 reference values of IOD for different populations. An IOD of 26.7 and 25.6 mm was 196 observed in American males and females, respectively.13 In the Indian population, the 197 reported overall mean IOD was 26.89 mm, while in males and females, the mean distance 198 was 27.46 mm and 25.93 mm, respectively.1 In the present study, the observed IOD values 199 (males: 19.79±1.46; females: 19.12±1.52) were lower than those reported in Indian and 200 American subjects. However, the mean IOD of Omani subjects was close to that of the 201 7 Iranian population (males: 23 mm; females: 21.7 mm).25 In previous studies, the observed 202 normal IZD was within the range of 90 mm and 109 mm.1,26,27 In line with these studies, the 203 interzygomatic distance in Omani subjects is found to be within this range. 204 205 The variations in orbital dimensions among different populations world-wide could be 206 attributed to the evolutionary processes wherein inheritable mutations can generally occur by 207 natural selection. As a result, population-based differences reflect contemporary 208 environmental pressures, genetic drift, historical and present hybridization between 209 geographically disparate populations, and current selective adaptation of human varieties to 210 their surroundings.28 In forensic anthropology, human skeletal remains are considered strong 211 evidence for population origin identification and identification of other factors, including sex, 212 age, and stature. Therefore, the reference values of orbital dimensions reported in the present 213 study are important in anthropological characterization. These values are also crucial for the 214 diagnosis as well as while planning the surgical treatments for various orbital pathologies. 215 The present study has the following limitation. As the present study is a single-centered 216 study, the study sample may not be a true representative of the Omani population. A multi-217 centered study considering the ethic differences of Omani subjects would be more interesting 218 to explore. 219 220 Conclusion 221 Results of the present study provide reference values of orbital dimensions in Omani subjects. 222 The prevalent orbital type of Omani subjects is mesoseme, which is a hallmark of the white 223 race. Further, these findings may be helpful in the field of forensic medicine and 224 anthropology and also for ophthalmologists and neurosurgeons and maxillofacial surgeons. 225 226 Conflicts of interest 227 The authors declare that they have no conflict of interest. 228 Funding 229 The present study is an unfunded project. 230 231 Authors contributions 232 Study conception and design: EA, HD, SRS; Material preparation and investigation: EA, MS, 233 MM, SRS; Formal analysis: MM, SRS, Validation of the data collection and results analysis: 234 EA, SRS, HD; Visualization and/or presentation of data: EA, MS, SRS, HD; Original 235 8 manuscript preparation: EA, MS, MM, SRS. All authors have read and approved the final 236 version of the manuscript. 237 238 References 239 1. Gupta V, Prabhakar A, Yadav M, Khandelwal N. Computed tomography imaging-based 240 normative orbital measurement in Indian population. Indian J Ophthalmol 2019; 241 67(5):659-663. doi: 10.4103/ijo.IJO_1187_18. 242 2. 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Axial CT image at the level of the orbits shows (a) the horizontal orbital distance of 319 the right orbit and (b) a sagittal image shows the vertical orbital distance 320 321 Table 1: Comparison between left and right orbital dimensions. 322 Parameters Mean± SD P value OI% Left orbit Right orbit 83.83±4.93 82.67±5.36 0.05 11 VDO (mm) Left orbit Right orbit 33.01±1.89 32.83±1.90 0.003 HDO (mm) Left orbit Right orbit 39.42±1.66 39.76±1.75 0.05 OI: orbital index; VDO: vertical distance of orbit, HDO: horizontal distance of orbit 323 324 Table 2: Associations of orbital dimensions with respect to gender on right and left sides 325 of orbit. 326 Parameters Mean± SD P value ROI (%) Female Male 82.49±4.93 82.85±5.77 0.59 LOI (%) Female Male 83.82±4.71 83.83±5.16 0.99 RVDO (mm) Female Male 32.44±1.79 33.22± 1.95 0.001 LVDO (mm) Female Male 32.71± 1.76 33.31±1.98 0.01 RHDO (mm) Female Male 39.37±1.56 40.16±1.84 0.001 LHDO (mm) Female Male 39.07±1.57 39.77±1.68 0.001 ROI: right orbital index, RVDO: right vertical distance of orbit, RHDO: right 327 horizontal distance of orbit, LOI: left orbital index, LVDO: left vertical distance of 328 orbit, LHDO: left horizontal distance of orbit. 329 330 Table 3: Comparison between orbital indices of different age groups among females. 331 Side Age Frequency Mean (%) Standard deviation P value Right 18-25 5 82.78 5.49 0.93 26-35 7 82.66 3.6 36-45 19 82.49 3.9 46-55 20 81.63 5.17 56-65 24 81.76 4.36 66-75 38 82.85 5.77 ≥76 24 83.25 5.11 Left 18-25 5 84.06 5.04 0.89 26-35 7 83.54 3.05 36-45 19 83.44 4.43 46-55 20 83.9 4.88 56-65 24 82.71 3.26 12 66-75 38 84.44 5.13 ≥76 24 84.17 5.82 332 Table 4: Comparison between orbital indices of different age groups among males. 333 Side Age Frequency Mean (%) Standard deviation P value Right 18-25 18 81.61 5.04 0.35 26-35 14 83.49 6.21 36-45 11 80.12 5.20 46-55 10 83.52 4.76 56-65 16 82.16 4.41 66-75 35 84.46 7.26 ≥76 32 82.55 4.99 Left 18-25 18 83.40 4.79 0.34 26-35 14 84.07 5.12 36-45 11 80.96 5.07 46-55 10 79.44 5.33 56-65 16 83.64 3.02 66-75 35 85.34 5.61 ≥76 32 83.53 5.57 334