Orbital indices in a modern Sinhalese Sri Lankan population

Abstract

The orbits are craniofacial structures situated on either side of the sagittal plane within the skull that encroach equally upon the cranial and facial regions. Each orbit is composed of several bones arranged to form quadrilateral pyramids with their bases facing anterolaterally and slightly downward, and their apices projecting posteriomedially. [1][2][3] The orbits contain and protect the eyes, extra-ocular muscles and several neurovascular structures, and also allow for the accurate positioning of the visual axis, [1,4] which is essential for binocular vision. As landmark features of the skull, morphometric characterisation of the orbits is of value for anthropology, [5] tracing population origins, gaining insight into craniofacial growth due to racial and sexual differences, [6] and quantifying intraspecific variations and forensic osteology. [1,2,4,7] Moreover, comprehensive assessment and preoperative planning in areas of neurosurgery, craniofacial surgery, congenital disfigurement and trauma require specific morphometric data on orbit morphology for the safety and efficacy of clinical treatment. [8][9][10][11] While orbit morphology has not changed significantly over recent human history, advances in surgical practice means that we are now able to utilise more detailed and specific information for the treatment of patients. [12] Thus, obtaining data elucidating intraspecific variation, such as left right symmetry (laterality), sex, and racial differences in the morphological parameters of the orbit Orbital indices in a modern AbstractObjectives: An understanding of orbital morphology is relevant to forensic identification, craniofacial surgery, and anthropological analysis. Orbital index (OI), the relationship between the height and width of the orbit, varies between different populations of humans. This study examines modern Sinhalese Sri Lankan skulls to determine normal values for OI and explore how OI may vary with laterality and sex.Methods: Measurements of fifty modern Sinhalese Sri Lankan skulls (origin Central Province, Sri Lanka) of known sex (34 male and 16 female) were undertaken for orbital height and width (bilaterally) using a digital caliper. OI was calculated using a standard formula ([orbital breadth / orbital height] × 100). Statistical tests analysing OI and size for both sex and laterality were performed using unpaired and paired 2-tailed t-tests (p<0.05), respectively. Results:Overall mean (±standard deviation) OI was 81.29±6.14, with significant differences found between males (79.29±5.65) and females (84.39±5.59) OI. Left OI was significantly greater than right in both males (80.74±5.85 vs. 77.83±5.11) and females (85.47±5.70 vs. 83.31±5.39), indicating OI asymmetry. Individual heights and breadths of the orbits were symmetrical in both males and females. Conclusion:Findings indicate OI asymmetry (left larger than right OI) and sexual dimorphism in this population of modern Sinhalese Sri Lankan skulls. Male orbits were microseme (OI<83) and female mesoseme , an unexpected finding ...