Sir:FigureAn understanding of orbital anatomy is necessary for safe repair of the bony orbit, as iatrogenic injury to the optic nerve at the time of surgery can lead to blindness. Several case series from the adult literature indicate that the incidence of postoperative vision loss is between 0 and 8.3 percent, and was 0.3 percent in the largest of these series.1–4 Nevertheless, postoperative vision loss can be devastating, and every effort should be made to avoid iatrogenic injury to the optic nerve. Orbital dimensions are well established in adults. Adult orbital depth is 45 mm, and this is a reliable approximation of the distance from the inferior orbital rim to the point at which the optic nerve exits the optic canal.5 It is at this point that the risk for direct injury to the optic nerve is most substantial. Consequently, this area should be avoided at the time of fracture repair if possible. Although orbital depth has been characterized in adults, it has not been measured in pediatric patients. Consequently, the aim of this study was to measure orbital depth in pediatric patients, to facilitate safer orbital fracture repair. The present study is a retrospective analysis of maxillofacial computed tomographic scans of patients aged 1 month to 17 years at Helen DeVos Children's Hospital between 2005 and 2009. Patients were stratified into 14 age groups. Each of these groups was composed of randomly selected computed tomographic scans from 15 girls and 15 boys, for a total of 420 patients included in the study. No scans demonstrating orbital fractures were used in this study. The primary outcome variable was mean orbital depth, as measured from the center of the inferior orbital rim to the point at which the optic nerve exits the optic canal (Fig. 1).Fig. 1: Depiction of orbital depth (dashed line). For the purposes of measurement in this study, the caudal-to-cranial distance from the inferior orbital rim to the level of the optic nerve where it exits the optic canal and the anterior-to-posterior distance from the inferior orbital rim to the optic nerve where it exits the optic canal form two perpendicular sides of a triangle; orbital depth is the third side of the triangle.Table 1 shows mean orbital depth by age. In the 0- to 6-month age group (infancy), orbital depth was 28.9 mm, which is 64 percent of the adult value (45 mm). There is a subsequent gradual increase in mean orbital depth with increasing age. Two other notable points are ages 3 and 8 years, with mean orbital depths of 85 and 95 percent of the adult values, respectively.Table 1: Mean Orbital Depth by AgeAn analysis of pediatric orbital depth was the goal of this study. Orbital depth proves important because it is at this deepest part of the bony orbit that the optic nerve is most vulnerable to injury. Analysis of these data shows that orbital depth is already 64 percent of its adult value in infancy. Furthermore, orbital depth is 85 percent of its adult value at age 3 years, and has reached 95 percent of its adult value at age 8 years. Thus, orbital depth at age 8 years closely approximates orbital depth in adulthood, and fracture repair can proceed with the knowledge that the segment of the optic nerve most vulnerable to injury is in nearly the same position as in the adult patient. Information provided in this study should enable the reconstructive surgeon to accomplish safer repair of pediatric orbital fractures, limiting postoperative vision loss. Matthew D. Martin, M.D. Grand Rapids Medical Education Partners/Michigan State University General Surgery Residency Program, Grand Rapids Medical Education Partners/Michigan State University Plastic Surgery Residency Program Benjamin P. Rechner, M.D. Grand Rapids Medical Education Partners/Michigan State University Plastic Surgery Residency Program, and, Helen DeVos Children's Hospital, Grand Rapids, Mich.
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Apr 18, 2013
Joshua R Bedwell + 1
Open Access
