Thread: Ophthalmology Clinical Case

Paramedics bring a 55-year-old woman to the emergency department after she was shot above the right eye with a BB gun. The patient is alert and awake, but she is irritated and complains of pain with decreased vision in her right eye. She has no other associated injuries.

On physical examination, her right upper eyelid is mildly edematous with a noticeable puncture wound at the BB entrance site marked by a drop of blood. The right eye is visibly proptotic, and the sclera is injected with chemosis. The patient has restricted movement of the affected eye. The pupil is round, 2 mm in diameter, and minimally reactive to light. She has no light perception in that eye. The pupil of the unaffected eye is 4 mm and briskly constricts to 2 mm with light. Repeated bedside testing with a Tonopen shows intraocular pressures (IOPs) of 75-80 mm Hg in the right eye with a normal IOP of 10 mm Hg in the unaffected, left eye. Instillation of fluorescein reveals no corneal damage. Her vital signs are remarkable for an increased heart rate of 102 bpm and a blood pressure of 163/84 mm Hg. The remaining physical examination findings are unremarkable.

What emergency condition do the increased IOP and proptosis indicate (see Image)?

[HIDE]Acute orbital compartment syndrome (AOCS): AOCS is an ophthalmologic emergency. Patients may have AOCS after blunt or penetrating trauma or after recent retrobulbar anesthesia (eg, for facial surgery) with the formation of a retrobulbar hematoma. The hematoma increases the IOP, compromising blood flow from the ophthalmic artery and leading to compartment syndrome. In addition, the globe itself can be forced anteriorly into the orbital rim. The medial and lateral canthal tendons tether the globe to the orbital rim and prevent the release of pressure, resulting in proptosis and, more importantly, a precipitous rise in IOP. Compression of the optic nerve and the central retinal artery leads to ischemia with vision loss in the affected eye unless the increased pressure is promptly relieved. Permanent ischemic complications may occur with as little as 2 hours of increased pressure.

The treatment for AOCS is emergency lateral canthotomy and cantholysis. This procedure is not considered standard of care for most primary care physicians, but in the proper setting, it may be appropriate as a vision-saving maneuver (eg, emergency medicine). The goal of the procedure is to reduce pressure in the globe to permit blood flow in the central retinal artery and the vasculature of the optic nerve. Primary indications for this procedure include decreased visual acuity, proptosis, pale optic disk on funduscopy, afferent papillary defect, or IOP >40 mm Hg in the setting of obviously increased retrobulbar pressure. A contraindication is rupture of the globe, which results in a nonround, pointed pupil; decreased turgor of the globe; or a positive Seidel sign (leak of aqueous humor at site of rupture seen with fluorescein staining). Patients without compromised visual acuity or markedly elevated IOP should be closely monitored while an ophthalmologist is consulted on an emergency basis. CT scanning or MRI may help in elucidating the etiology of the compression or establishing the diagnosis.

To reduce IOP, all patients with AOCS should be treated with intravenous mannitol (to promote direct osmosis of fluid), acetazolamide (to decrease production of aqueous humor), topical beta-blockers (to decrease production of aqueous humor), and methylprednisolone (to control inflammation).

To perform lateral canthotomy and cantholysis, lidocaine 1-2% with epinephrine should first be injected into the lateral canthus if the patient is conscious. A small hemostat is then used to grasp and crimp the skin of the lateral canthus for at least 1 minute to not only mark the area for the incision but also facilitate hemostasis. By using scissors, a lateral incision is made in the lateral canthus down to the orbital rim (approximately 1-2 cm deep). This maneuver partially reduces IOP and allows access to the superior and inferior crus of the lateral canthal tendon. By taking care to avoid puncturing the globe, the inferior crus of the lateral canthal tendon should be released next. If the IOP is <30 mm Hg, the procedure should be stopped. If the IOP continues to be >40 mm Hg, the superior crus of the lateral canthal ligament should also be released from the orbital rim. After the lateral canthal tendon is release, the IOP should decrease to <30 mm Hg.

If the patient is conscious, he or she may report improved visual acuity in the affected eye after the procedure. Complications include hemorrhage, mechanical injury to the globe, and intraocular infection. The patient in this case underwent lateral canthotomy with release of the inferior crus of the lateral canthal ligament. Vision in the affected eye was partially restored. [/HIDE]

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