Cauterization-mediated restriction from penetrating orbital trauma

Abstract

A healthy 32-year-old woman presented with binocular diplopia immediately after sustaining a penetrating injury to the left periocular adnexa with a hot metal skewer. Examination revealed an incomitant esotropia, with complete limitation of abduction of the left eye with downshoot in left gaze and normal afferent visual function. Computed tomography and magnetic resonance imaging demonstrated no fracture, but there was mild thickening of the medial rectus muscle and associated fat stranding. Lack of orbitomuscular tethering or hematoma led to the presumptive diagnosis of thermal cauterization injury causing left medial rectus restriction. Given the lack of literature on this mechanism of injury, the patient was monitored closely. She exhibited remarkable spontaneous improvement in motility over 6 months, with near orthophoria in primary gaze. However, bothersome residual esotropic diplopia in left gaze prompted a left medial rectus recession, with a good outcome. This case demonstrates that isolated extraocular muscle thermal injuries and consequential strabismus can recover spontaneously; longitudinal observation before surgical intervention may be appropriate in such cases.

Case Report

A 32-year-old woman presented with left eye pain, blurred vision, and oblique binocular diplopia 7 hours after being struck with a hot metal skewer. While roasting marshmallows, her husband’s marshmallow and shirt caught fire. Attempting to extinguish the fire while still holding his skewer, he accidentally struck the patient just nasal to the left eye with the hot, metallic skewer. She recalled immediate pain and went to a bathroom to rinse her eye. Upon opening the eye, she noted oblique binocular diplopia and a deficit in left eye motility.

Noncontrast orbital computed tomography (CT) at a local hospital demonstrated trace bleeding and a small focus of gas in the inferomedial orbit, with no other injuries. There were no fractures. She received vancomycin and ceftazidime intravenously and was transferred to a tertiary referral center. She denied any ophthalmic history and had hypothyroidism.

On examination, visual acuity was 20/30⁺³ in the right eye and 20/60⁺¹ with pinhole improvement to 20/30 in the left eye. Color perception (by Ishihara plates) was full in each eye. There was no relative afferent pupillary defect. The left pupil was noted to be ~1 mm larger than the right. Extraocular motility testing demonstrated complete limitation of abduction and mild limitation of supraduction in the left eye, with a downshoot in the left eye on attempted left gaze (Figure 1A). Prism cover testing revealed a 40^Δ esotropia and an 18^Δ left hypotropia in primary gaze. There was a small inferonasal corneal epithelial defect and a 7 mm radial, inferonasal conjunctival laceration, with scattered subconjunctival dark particulate debris (Figure 1B). Intraocular pressures and dilated funduscopy were normal.

FIG 1.

Ocular alignment and motility, external findings and imaging shortly after penetrating thermal injury to the left nasal orbit. A, Horizontal ocular motility photographs (within 1 day of surgery) with depictions in right gaze (left), primary gaze (middle), and left gaze (right). B, Slit lamp photograph taken in up-and-left gaze, with the lower lid manually lowered showing subconjunctival debris that marks the location of penetrating injury (note, photograph taken 8 months after initial injury). C, Magnetic resonance images: midorbital axial T1-weighted postgadolinium with fat suppression (left), retrobulbar coronal short tau inversion recovery (T2-weighted, fat suppressed) sequence.

Gadolinium-enhanced, orbital magnetic resonance imaging (MRI) the following morning demonstrated soft-tissue stranding of the medial orbit, with mild enhancement and thickening of the medial rectus muscle, without hematoma (Figure 1C). Pain lessened, although diplopia with complete abduction limitation persisted. Visual acuity improved to 20/25 in the left eye. She was discharged on oral amoxicillin-clavulanate and topical moxifloxacin and erythromycin.

Repeat examination 10 days after injury showed further improvement of uncorrected visual acuity to 20/20 in the left eye. Stereopsis was absent to Titmus Fly. There was complete limitation of abduction in the left eye and a 25^Δ esotropia in primary gaze (15^Δ near). Forced ductions achieved full abduction in the left eye, with mild-moderate resistance and without globe retraction. Saccadic extraocular motility and alignment were unchanged after forced ductions, effectively excluding a reversible tethering/entrapment mechanism. The presumptive diagnosis was left medial rectus cauterization injury with possible fat adhesion.

There were no significant changes in stereoacuity or alignment 1 month after the previous examination, but abduction improved to −2.5. Two months after injury, anisocoria was reversed, with the right pupil larger than the left. She had regained stereoacuity to 60 arcsec, and extraocular motility improved in the left eye to −0.5, with 12^Δ esotropia and 10^Δ left hypotropia in primary gaze (10^Δ intermittent esotropia and 5^Δ intermittent left hypotropia at near) increasing to 20^Δ esotropia and 14^Δ left hypotropia in left gaze (Figure 2A). Over subsequent visits 3, 4, and 6 months after injury, anisocoria persisted without gaze-evoked changes in magnitude or lid position. Stereoacuity improved to 40 arcsec, with restoration of full abduction and decrease of her horizontal deviation to a 2^Δ esophoria and no vertical deviation in primary gaze (Figure 2B–D). However, diplopia in left gaze with 10^Δ of esotropia persisted and was very bothersome to the patient, reportedly causing flashbacks to the traumatic event.

FIG 2.

Recovery of ocular alignment and motility. A-D, Horizontal ocular motility photographs with depictions in right gaze (left), primary gaze (middle), and left gaze (right) 10 days (A), 3 months (B), 4 months (C), and 6 months (D) after the initial injury. E, Postoperative photographs taken 15 months after surgery, which was performed 9 months after injury.

She elected to undergo strabismus surgery 8 months after the injury. A 2 mm left medial rectus recession was performed on an adjustable suture. Intraoperatively, a Stevens hook was advanced posteriorly between the muscle and globe to separate potential posterior adhesions. Persistent diplopia in left gaze on postoperative day 1 prompted two sequential adjustments to a net recession of 6 mm, which improved her diplopia. On follow-up 15 months postoperatively, the patient had no symptomatic diplopia, 40 arcsec of stereoacuity, and remained orthophoric in primary gaze at distance (6^Δ exophoria at near with convergence to the nose; 2^Δ esophoria in left gaze) (Figure 2E).

Discussion

Ocular thermal burns are most frequently encountered in the context of exposures to direct flame, hot liquids, blast injuries, or handheld heat sources (eg, cigarettes, curling irons); these injuries most commonly affect the eyelid and external adnexa because of the protective effects of the blinking and Bell’s reflexes.^1,2 To our knowledge, this is the first report in the English literature of penetrating thermal burn injury of a human extraocular muscle; a PubMed query of all available years of MeSH derivations of extraocular/oculomotor muscle thermal/burn/injury yielded no relevant publications.

Post-traumatic limitation of extraocular motility can result from neurologic injury, disruption of orbital anatomy (including muscle entrapment), direct muscle injury (intramuscular bleeding, avulsion or laceration), or scarring. A neurogenic cause of our patient’s abduction limitation is implausible, given the injury site. However, reversing anisocoria suggests some element of neurogenic injury, albeit without clear evidence of aberrant regeneration. Likewise, a history of penetrating injury should raise concern for direct extraocular muscular injury, and our notation of mild-moderate restriction on forced abduction supported a mechanical/restrictive mechanism. Commonly encountered restrictive mechanisms resulting from trauma include intramuscular hematoma, muscle entrapment in a fracture, and foreign body and adhesion following scarring, all of which were excluded in this case by imaging and examination (including intraoperatively). Thus, the presumptive diagnosis was cauterization injury of the medial rectus muscle. The vertical deviation could be attributed to greater involvement of the inferior medial rectus compartment and/or concomitant involvement of the inferior rectus or superior oblique muscles.

We posit that this patient’s penetrating injury effectively induced a thermal tendinoplasty of the medial rectus muscle, akin to a muscle shortening procedure. A plausible clinicalpathological correlate may be found in a 1987 report by Finger and colleagues,³ wherein bipolar unidirectional cautery of the tendinous portion of extraocular muscles in Rhesus monkey produced effective and functional shortening of the muscle. Normal tensile strength was retained 2 months later, with demonstration of shrinkage and compaction of collagen bundles in the muscle tendon histologically. Secondary contracture of uninjured medial rectus fibers may have limited full spontaneous recovery. Corticosteroids and/or botulinum toxin injection were considered but ultimately not pursued because published clinical evidence was lacking, and there was concern for anatomic disruption of the putative injection site.

Although our patient ultimately underwent strabismus surgery, she exhibited substantial spontaneous improvement in extraocular motility in the months following her injury. Extraocular muscles exhibit robust regenerative capacity owing to a large and active population of myogenic precursor/“satellite” cells.⁴ She notably required a relatively large recession to relieve residual restriction, with preservation of alignment in primary gaze postoperatively, suggesting that the muscle’s contractile properties may have also been altered. Our case suggests that it may be advisable to delay surgical intervention for strabismus secondary to extraocular muscle thermal injury to allow for spontaneous improvement.

Literature Search

PubMed Central was searched on October 8, 2023, and June 15, 2023, for all available years: (“oculomotor muscles” [MeSH Terms] OR (“oculomotor” [All Fields] AND “muscles” [All Fields]) OR “oculomotor muscles” [All Fields] OR (“extraocular” [All Fields] AND “muscle” [All Fields]) OR “extraocular muscle” [All Fields]) AND (“thermal” [All Fields] OR “thermalization” [All Fields] OR “thermalize” [All Fields] OR “thermalized”[All Fields] OR “thermalizes” [All Fields] OR “thermalizing”[All Fields] OR “thermally”[All Fields] OR “thermals” [All Fields]) AND (“injurie” [All Fields] OR “injuried” [All Fields] OR “injuries” [MeSH Subheading] OR “injuries”[All Fields] OR “wounds and injuries” [MeSH Terms] OR (“wounds”[All Fields] AND “injuries” [All Fields]) OR “wounds and injuries” [All Fields] OR “injurious” [All Fields] OR “injury s” [All Fields] OR “injuryed” [All Fields] OR “injurys” [All Fields] OR “injury” [All Fields]).