New insights into facial anthropometry in digital photographs using iris dependent calibration
Introduction
For centuries, anthropologist and physicians have attempted to objectively assess the craniofacial anatomy. Apart from documentation, objective assessment and measurements of craniofacial anatomy can be helpful for planning and evaluating reconstructive and aesthetic facial surgery. A large number of different methods have been described to objectify the facial anatomy. Direct clinical measurements, as described by Farkas [1], [2], [3] and manual measurements in photographs [4], [5] are the most common means by which the anatomy is assessed, but measurements in cephalometric radiographs [6], [7], [8] and recent three-dimensional digital stereophotogrammetry [9], [10], [11], [12], [13] have also been described. Anthropometry using photographs has obvious advantages over other methods. It is non-invasive, inexpensive, fast, reproducible and the images can be archived for future evaluation [5], [14], [15]. Direct clinical measurements are laborious and dependent on patient compliance. This makes photo-anthropometric analyses particularly useful when working with children.
Computer-assisted anthropometry in digital photographs to analyze anatomy and evaluate postoperative results have been described previously [5], [14], [16], [17]. A problem arises however, when an attempt is made to assess pre-existing photographs, since consistent measurements only seem possible when a scale was included in the photograph. We propose that it is possible to perform consistent measurements in photographs without a scale included by using iris dependent calibration of the photograph. The key here is the extraordinary constancy of the iris diameter. The iris diameter has been object of many ophthalmic studies which have demonstrated that adults have a very narrow spread of the (horizontal) diameter of the iris of 11.6–11.7 ± (0.32–0.58) mm [18], [19], [20]. This constancy of the iris diameter would permit calibration of pre-existing frontal photographs, and this technique has been once previously applied in photographs of adults [21]. The question remains if it is also valid for use in photographs of children. Ophthalmic literature is not conclusive about the completion of corneal growth, but there are indications that the majority of corneal growth occurs before the age of one and the cornea completes its growth at the age of 5 [22], [23]. This would indicate that iris dependent calibration is a useful technique in assessment of photographs of children from 5 years onward.
Our aim was to establish a new, objective, easy-to-use, computer-assisted technique for facial anthropometry in digital photographs in children and young adults using iris dependent calibration and to examine the validity of this technique in different coronal planes of the craniofacial region. With the use of iris dependent calibration one can easily assess facial anatomy and (even retrospectively) evaluate preoperative and postoperative photographs without the need for a scale in the photograph.
Section snippets
Methods
We photographed 100 children to evaluate the constancy of the iris diameter in children for future assessment using iris dependent calibration of photographs.
Participants
We assessed the photographs of 100 consecutive participants. This group had a mean age of 10.57 ± 3.96 years, ranging from 5 to 18 years. The mean age and distribution of ages between boys and girls were the same (p = 0.848).
Horizontal iris diameter (IDh)
All photographs of our participants met our photographic conditions, and the IDh could be quantified in each photograph. We measured the IDh*forehead of both eyes of our 100 participants, resulting in 200 values. The IDh*forehead ranged from 10.0 to 13.0 mm (Fig. 2). The mean
Discussion
The present study was designed to establish a new, objective, easy-to-use, computer-assisted technique for anthropometry of the facial anatomy. In plastic and reconstructive facial surgery objective assessment of preoperative and postoperative anatomy is important to evaluate surgical techniques and results. While computer-assisted anthropometry substitutes laborious clinical measurements, the need to simplify is obvious. To include a consistent scale in a photograph is not always feasible.
Conclusion
The present study is the first iris dependent calibration study for children, and indicates that the iris diameter has the same consistency from the age of 5 as in adults. This provides a technique for calibrating photographs that have no scale or grid included, and allows analysis of both later and earlier unscaled photographs using iris dependent calibration. This makes it possible to perform life-size measurements in a frontal view photograph. For facial structures outside the coronal plane
Conflicts of interest
There are no conflicts of interest.
Funding
There has not been any funding for this study.
Acknowledgements
The authors would like to thank all colleagues who contributed to this study and research paper. Special thanks to Dr Paul Nagtegaal for his useful suggestions.
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