Ethmoidal foramina: the rule 24-12-6: is it true for Indian orbits?

Aim : The literature states that the distances between the medial margin of the orbit to the anterior ethmoid foramen, from it to the posterior ethmoid foramen and from it to the optic canal are 24mm, 12mm & 6 mm. This study is to verify if this is true in the Indians as there is no data available in the literature. To the best of our knowledge it is the first study from India, which focused on the relationship of ethmoid foramina. Methods: 70 orbits of 35 Indian skulls were studied, using depth gauge, sliding calipers, dividers and metal scale by a single observer. Results: The average distance between the medial margin of the orbit and the anterior ethmoid foramen is 21.30mm and 20.37mm for right and left orbits respectively (range varying from 18 to 26mm in the right and from 14 to 26 in the left orbit). The average distance between the anterior and posterior ethmoid foramina is 12.45 and 12.47mm (range 6mm to 18mm). The average distance between the posterior ethmoid foramen and the optic canal is 6.32 and 7.37mm (range 2 mm to 18mm). 10 of 35 skulls (28.6%) had 3 foramina instead of 2 (accessory foramen), involving right orbit in 5, left in 4 and both the orbits of a skull. Conclusions: The rule 24-12-6 does not apply to Indian orbits. The anterior Ethmoid foramen is about 3mm nearer to the orbital margin. There is a great variation in the distances of ethmoid foramina. Nearly a third of the skulls have accessory ethmoid foramen.