Prospective Analysis of Strabismus and Diplopia Associated With Orbital Fractures: Determiniation of the Critical Size of Orbital Floor Defects Producing Diplopia

Abstract

Purpose:: Diplopia and strabismus are frequently associated with orbital fractures and are often cited as indications for repair. However, little is known about the critical size of orbital floor fractures that produce diplopia and strabismus. We have prospectively examined the incidence and character of diplopia and strabismus associated with isolated orbital floor fractures, then correlated these observations with fracture size.

Methods:: Adult patients presenting within 3 days of sustaining an isolated orbital floor fracture were offered enrollment. Patients with entrapment or additional injuries requiring immediate attention were taken to surgery and excluded from this study. Over 2½ years, 21 patients were recruited under an IRB-approved protocol. On presentation, each patient underwent a complete ophthalmic examination, including a detailed orthoptic evaluation by a trained technician. Vertical and horizontal strabismus were measured in prism diopters. Axial and coronal orbital CT scans were obtained. The area of each fracture was calculated as the product of the maximum width and maximum length of the fracture, estimated from serial 3mm sections.

Results:: Patients were divided into three groups based upon fracture size: small (<1cm²), medium (1-2cm²), and large (>2cm²). Diplopia within 20 degrees of fixation was observed in 0 of 5 patients with small fractures (0%), 2 of 7 patients with medium fractures (29%), and 9 of 9 patients with large fractures (100%). Patients with small fractures had neither vertical nor horizontal strabismus. Four patients with medium fractures had strabismus with an average deviation of 3 prism diopters of vertical deviation and no horizontal deviation. All patients with large fractures had strabismus, with an average vertical deviation of 7 prism diopters and an average horizontal deviation of 8 prism diopters.

Conclusions:: Our results correlate the incidence of strabismus and diplopia with fracture size and demonstrate that the critical size of the orbital floor defect is greater than 2 cm². In order to better understand the mechanism, we are utilizing magnetic resonance imaging (MRI) to examine extraocular muscle function in patients with orbital fractures. We plan on prospectively enrolling patients with fractures >2cm² for high resolution imaging of the extraocular muscles, though a previously established protocol, to better characterize the observed positive correlation between fracture size and strabismus

Keywords: strabismus: etiology • extraocular muscles: structure • imaging/image analysis: clinical