An experimental investigation of the safe distance for internal orbital dissection.

PURPOSE: The purpose of this investigation was to determine the distance from the orbital rim to the important soft tissues of the orbital apex using eight reference points to provide clinically useful information for surgical decision making.
MATERIALS AND METHODS: Eight human cadavers were used in this investigation. After circumorbital incisions were made and the canthal ligaments were detached, a careful subperiosteal dissection was performed to the soft tissues of the orbital apex. Four reference lines were established. The first two were based on a horizontal line drawn through the medial and lateral canthal ligaments and a perpendicular to this through the infraorbital foramen. The other two were created at points 45 degrees from the first two. Depth measurements were made with a straight probe at the eight points where the lines crossed the orbital rim. Means, standard deviations, and ranges were derived, and statistical differences were calculated between right and left orbits using a paired-samples t-test. Because no right and left differences were noted (P < .05), the data were pooled.
RESULTS: The mean distance from the orbital rim to the soft tissues of the orbital apex was 44.1 +/- 1.4 mm medially, 38.3 +/- 3.0 mm laterally, 44.5 +/- 1.72 superiorly, and 39.4 +/- 2.9 mm inferiorly. The superomedial distance was 46.3 +/- 2.7 mm, the inferomedial distance was 44.1 +/- 1.4 mm, the inferolateral distance was 41.4 +/- 2.5 mm, and superolateral distance was 39.4 +/- 2.8 mm.
CONCLUSIONS: The distances from the orbital rim to the soft tissues of the orbital apex varied among the eight different reference points (range, 38.3 +/- 3.0 mm to 46.3 +/- 2.7 mm). No distance was less than 31.0 mm or exceeded 51.1 mm. There was no difference noted (P < .05) between the right and left sides for each of the corresponding reference points.