Orbital indices in a modern Sinhalese Sri Lankan population

Abstract

Objectives: 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 (OI 83–89), an unexpected finding as Asian populations supposedly have megaseme (OI>89) orbits, therefore challenging previous assumptions on ethnic OI norms.

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