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Introduction
Safe and effective orbital surgery requires an extensive knowledge of the anatomy of the bony orbit and the morphometric relationships that exist within it. The medial orbital wall contains several osseous landmarks, which enable the orbital surgeon to assess the proximity to important structures such as the skull base, ethmoidal arteries and optic nerve. Classically, the medial orbital wall contains one anterior ethmoidal foramen and one posterior ethmoidal foramen. 1
Previous studies have documented the presence of multiple foramina but have not investigated the morphometric relationships between them. 1 2 The relationship of the anterior lacrimal crest to the anterior ethmoidal foramen, the anterior ethmoidal foramen to the posterior ethmoidal foramen and the posterior ethmoidal foramen to the optic canal is commonly referred to as being '24-12-6 mm'. 3 The aim of this study is to examine the validity of this anatomical relationship and the extent to which anatomical variation occurs within a British Caucasian population for which there are currently no published data.
A previous study has demonstrated that male orbits are morphometrically larger in a Chinese population. 2 However, these data remain inconclusive for Caucasian orbits. We aim to examine our orbits for the presence of sexual dimorphism. Right-left asymmetry has also been demonstrated in Chinese orbits but not conclusively in Caucasian orbits and is assessed in our cohort. 2
Our final objective is to calculate the approximate geometric relationships that exist between landmarks at the medial wall when approaching the orbital apex. In doing so, we propose guidelines for safe operating margins at the medial orbital wall and orbital apex.
Materials and methods
Forty-seven orbits from 24 formalin-fixed cadavers were exenterated. All the soft tissue within the orbit was removed, including the periosteum, allowing us to demarcate the relevant sutures, fissures and foramina. Twenty of the cadavers were donated between June 2007 and June 2009 and the other four were head and neck prosections from a collection stored at the anatomy department of St.George's Medical School. The male to female ratio was 11:13, respectively. Information regarding the cause of death of each cadaveric specimen was available of which none affected the normal anatomy of the orbit such as recent orbital surgery or trauma.
Measurements were taken using a surgical ruler...