Outer and Inner Canthal Distances and their Stature Estimation Potentials among Nigerian Igbos and Ibibios Residing in Rivers State, Nigeria

Gabriel Sunday Oladipo

https://orcid.org/0000-0002-1780-8992
Department of Anatomy, Faculty of Basic Medical Sciences, College of Health Sciences, University of Port Harcourt, Rivers State, Nigeria

Emmanuel Afolabi

https://orcid.org/0009-0002-6833-1220
Department of Surgery, Queen Elizabeth the Queen Mother Hospital (East Kent University Hospitals), Kent, United Kingdom

Bukola Blessing Johnson

Department of Anatomy, Faculty of Basic Medical Sciences, Madonna University, Elele, Rivers State, Nigeria

Oghenefego Michael Adheke

https://orcid.org/0000-0002-6306-279X
Department of Human Anatomy, Faculty of Basic Medical Sciences, Southern Delta University, Ozoro, Delta State, Nigeria

Introduction

The identification of individuals using the anthropometry of the human face remains an integral part of biological anthropology. The concept of facial anthropometry in anthropology deals with the measurement of physical components of human face in relation to their racial and ethnic differences (Jahanshahi 2012; Darkwah et al. 2018). Both the inner canthal distance (ICD) and outer canthal distance (OCD) of the canthi (the corners of the eyes where the upper and lower eyelids meet) are important facial measurements that are applicable in both anthropological and forensic studies (Oladipo et al. 2011; Yadav et al. 2019; Bahşi et al. 2021). Furthermore, the understanding of the variations between sexes and ancestries in the assessments of canthal anthropometry could be applied in reconstructive and cosmetic surgeries that usually involve carrying out surgical procedures that are aimed at correcting deformities and enhancing facial aesthetics (Raschke et al. 2013; Bouhadana et al. 2022; Celikoyar et al. 2022). Currently, it is generally accepted that there are morphological differences based on several literature on variations in canthal anthropometry among ethnic groups in Nigeria (Osunwoke et al. 2010; Anibor et al. 2014; Ogoun et al. 2021), and between ancestries globally (Yadav et al. 2019; Bahşi et al. 2021; Radha and Srinivasan 2021; Bouhadana et al. 2022; Ndombolo et al. 2024).

Together with sex, age and ancestry, the estimation of stature is a key biological means of identification in humans (Oladipo et al. 2015; Cunha and Ubelaker 2020). Despite the generalization of knowledge among anthropologists that support the accuracy and reliability of long bones as the most suitable body components for predicting stature across different racial populations (Cunha and Ubelaker 2020), the application of soft tissues in stature prediction has been gaining momentum in recent times. The profiling of unidentifiable human remains by forensic anthropologists to estimate stature using soft-tissue craniofacial measurements has become a common practice by various researchers in the field of biological anthropology (de Acuerdo and de la Cabeza 2015; El-Kelany et al. 2015; Yadav et al. 2019; Bashar et al. 2024). It is worthy of note that there are limited studies on the prediction of stature using canthal anthropometry in non-Negroid populations, and there are arguably none that has been studied using a Nigerian population. In estimating stature from canthal anthropometry, individuals can be positively identified especially in forensic cases where soft tissue remains are incomplete.

In south-southern Nigeria, some of the residents that live in the multilingual city of Port Harcourt (which is in Rivers State) are of Igbo and Ibibio ethnic extractions as the city is bordered by Imo and Akwa-Ibom states, respectively. Arguably regarded as the most populated region within southern Nigeria, Rivers State is not without its challenges that are usually associated with crimes, such drug abuse, human trafficking, and other forms of social vices (Abiodun et al. 2017; Joab-Peterside et al. 2021). These vices could in turn lead to deaths of victims found in such crime scenes thereby posing unique difficulties to local security agencies in trying to identify discovered victims. In high profile forensic cases, local anthropologists are consulted by these security agencies to assist in the forensic identification of the discovered victims – which could be challenging as well due to the lack of forensic databases in the region. Also, in line with studies done by Gao et al. (2024), and Chalkis et al. (2024), surgical outcomes could be affected by anatomical differences in eyelid shape, orbital structure, and overall facial proportions across different racial populations and these variations could in turn impact the selection of techniques and aesthetic consequences in oculoplastic surgeries. The current study was done to investigate the stature estimation potentials of outer and inner canthal distances among Nigerian Igbos and Ibibio adult populations residing in Port Harcourt, Rivers state.

Materials and Methods

A total of 300 adults (150 Ibibios and 150 Igbos) were randomly selected for this study and were limited exclusively to adults of Madonna University, Elele Campus in Rivers State of Nigeria. Minimum sample size was determined using Fisher’s formula for infinite population or population larger than 10,000 (Cocharan 1963). The subjects were from Ibibio and Igbo ethnic origins of Nigeria by both parents and genealogies and were between the age of 18 and 30 years. Subjects with outside age range of 18 and 30 years, those with any form of facial anomalies, prior facial surgeries and those from heterogeneous parents were excluded. Subjects were selected in line with the Declaration of Helsinki research ethics protocols for human research. Ethical clearance was obtained from the Research Ethics Committee of the University of Port Harcourt Teaching Hospital, Port Harcourt (with registration number NHREC/UPTHREC/03/2023 and protocol number, UPTH/ADM/90/S.11/VOL.XI/1722). All subjects gave their informed consent, and their personal information were kept confidential.

The measurement of inner canthal distance [ICD] and outer canthal distance [OCD] were carried out with the aid of transparent meter rule and recorded in centimeters (cm). The distance between the lateral canthi of the right and left eyes gave the outer canthal distance while the distance between the medial canthal of the right and left eyes gave the inner canthal distance [Figure1]. Height (stature) was measured with the aid of a stadiometer and recorded in cm. Subjects were barefooted (thin socks were also allowed). Subjects were asked to stand on the base of the stadiometer in an erect position. The heels were placed together and arms relaxed at the sides. The head board of the stadiometer was adjusted to the top of the head (vertex) and readings were taken from the calibrations of the stadiometer. 2) All the measurements were performed twice and average of the two scores were used for precision purpose. Reading was taken to two decimal places.

Statistical Analyses

Raw data collected from the subjects were recorded in a Microsoft Excel 2019 version and analyzed using the Statistical Package for Social Sciences (SPSS version 20.0). Differences between sexes and ethnic groups in canthal distances and heights were determined using the independent sample t-test while test of association was done with the aid of Pearson’s correlation and regression analyses. Confidence interval was set at 95%.

Results

The results of the various analyses are presented in table 1 to 8. In the general population [Table1], males had a mean height of 180.57±0.74 cm while females had a mean height of 175.28±0.65 cm. The mean ICD in males was 3.31±0.02 cm while in females it was 3.35±0.02 cm. The mean OCD was 11.52±0.04 cm in males and 11.23±0. 04 cm in females.

Using independent sample t-test to compare the above variables between males and females, it was observed that there was a statistically significant difference in the mean height of males and females (p<0.05) with males showing significantly higher value than females. Also, there was a statistically significant difference between the mean OCD of males and females (p<0.05) with males showing higher mean OCD than females. However, no significant difference was observed between the mean ICD of males and females (p>0.05).

Table 2 contains the results of the ethnic comparison of Height, OCD and ICD between Igbos and Ibibios. The mean heights of the Igbo and Ibibio subjects were 177.87±0.69 cm and 177.98±0.76 cm respectively. Those of ICD were 3.36±0.17 cm and 3.31±0.12 cm respectively while the mean OCD for Igbos and Ibibios were 11.39±0.04 cm and 11.36±0.04 cm respectively. It is worthy of note that the difference in the mean heights of the Igbos and Ibibios were not statistically significant (p>0.05). Also, the mean OCD in the Igbos and Ibibios were not statistically significant (p>0.05). However, there was a statistically significant difference between the mean ICD of the Igbos and the Ibibios (p<0.05) with Igbos showing higher mean value.

Table 3 to 6 show the descriptive statistics for height, ICD and OCD of Igbo males and females, Ibibio males and females, Igbo males and Ibibio males and Igbo and Ibibio females respectively. Regression products of the correlation of height and ICD and OCD are shown in table 7 and 8. It can be observed that Pearson R value for the correlation between height and ICD in males is 0.507. This correlation is statistically significant (p<0.05). Although the correlation between height and OCD in males with R value 0.172 is weak, it is however statistically significant (p<0.05). On the other hand, no significant correlation was observed between ICD and height (R=0.121, p>0.05). In females, there was a weak but statistically significant correlation between OCD and height (R=0.200 p<0.05).

On carrying out the linear regression to obtain the linear relationship between height, OCD and ICD in females, the Pearson constant (C) which indicates the Constant value in a linear equation and the slope (R coefficient) was obtained as shown in table 7. The derived equations follow the linear equation y = mx+c and are represented in table 8. This could be used to determine the height of males and females when the ICD and OCD is measured accurately.

Discussion

It is true that the understanding of the anatomy of the human face brings to light a myriad of applications in the subject fields of ophthalmic, reconstructive, and plastic surgeries, as well as anthropometric evaluations in both forensic and biological identification. As stated earlier, the anthropometric profiling of human subjects by various anthropologists to estimate stature (height) using soft-tissue craniofacial measurements has become a common practice by various researchers in the field of biological anthropology (de Acuerdo and de la Cabeza 2015; El-Kelany et al. 2015; Yadav et al. 2019; Bashar et al. 2024). However, this study is arguably the foremost research that has been done with regards to the relationship between stature, inner (ICD) and outer canthal distances (OCD) for any given Nigerian population.

The present study showed that the mean ICD in males and females were 3.31 cm and 3.35 cm respectively, while the mean OCD in males and females were 11.52 cm and 11.23 cm, respect­ively. A related study done to evaluate the ICD in a Saudi population reported from their results that the mean ICD when the sexes were combined was 3.03 cm (ranging from 2.22 cm to 3.78 cm), with a mean ICD of 3.11 cm for males, and a mean ICD of 2.96 cm for females (Hamid et al. 2021). Earlier, a research by Ozturk et al. (2006) on a Turkish population found that the males and females had a mean ICD of 3.07 cm and 3.03 cm, respectively, while El-Sheikh et al. (2010) reported mean ICD values for a Sudanese population to be slightly higher compared to this present study to be 3.34 cm and 3.24 cm for their males and females, correspondingly. Furthermore, studies done using different south Asian populations by Adhikari et al. (2016), and Iqbal et al. (2024) both revealed similar findings to the present study results on Ibibio population that the males had higher ICD values in association with the female subjects. Within Nigeria, Oladipo et al. (2011) had earlier reported from a survey of 800 participants from Ibibio ethnic group that the ICD of males and females were 3.52 cm and 3.36 cm, respectively – which is in line with the present study that showed that the Ibibio males had a mean ICD of 3.32 cm while their female counterparts had a mean of 3.29 cm. However, the ICD values of the Igbo population in this present study showed a higher mean for the females (3.42 cm) compared to the male counterparts (3.30 cm).

As seen in this study, the average OCD in males for both ethnic groups were slightly higher compared to the female counterparts. These results were in accordance with the studies done among certain ethnicities in Nigeria by Oladipo et al. (2009), Osunwoke et al. (2010), and Anibor et al. (2014). How­ever, in comparisons to other racial populations, the OCD was higher as the mean OCD for a studied population by Rajput et al. (2022) was 9.23 cm for males and 7.31 cm for females while another related study done by Srivastava et al. (2023) using an Indian population noted from their results that the mean OCD was 8.23 cm for males and 7.22 cm for females. Furthermore, similar research done to evaluate OCD using both Indian and Nepalese undergraduate students (Adhikari et al. 2016) revealed that the males had respective higher OCD values (9.49 cm and 9.35 cm) in association with the female subjects (9.13 cm and 9.15 cm) – which agrees with the current study despite reporting higher values in comparison to the south Asian subjects. It could be explained that a host of diverse factors such as changes in lifestyle and dietary habits have had a direct relation to human growth and development over the years and these factors, which are generally population-specific, can affect the morphology and morphometry of the faces among the studied ethnicities.

Suffice it to say that despite that there are some works that has been done to estimate stature (height) using selected facial and nasal parameters (Kumar and Chandra 2006; Kalia et al. 2008; Agnihotri et al. 2011; Wankhede et al. 2012), it has proven to be a challenge to come across studies that have used periorbital (or canthal) parameters to predict stature talk less of a Nigerian population. The applications of both ICD and OCD in stature prediction were shown to be relevant in this study as there were significant relationships between both canthal parameters and height in both sexes irrespective of ethnic differences using the Pearson correlation. These study observations were followed up by deducing linear regressions for estimating the height in males and females based on the measured ICD and OCD values. Although this study was able to establish the significant relationships between stature, ICD and OCD, the researchers recognize that these observations do not make up for a possible generalization of the total population of Nigerian Igbos and Ibibios due to the limited sample size.

Conclusion

The study concluded that there were significant differences in both sexes despite no ethnic differences in terms of stature, ICD and OCD. Also, there were strong associations between both canthal parameters and height in both sexes irrespective of ethnic differences. These study values could assist local ophthalmic, reconstructive, and plastic surgical practitioners who practice in both ethnic regions in managing surgical issues related to the human face. Also, this study could enable local anthropologists and researchers to digress further on analysing the applications of canthal anthropometry in the prediction of stature across different ethnicities in Nigeria, thereby adding to the growth of physical and forensic anthropology in the country.