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Q1: What is orbital compartment syndrome and why is it a medical emergency?
Orbital compartment syndrome (OCS) results from increased pressure behind the eye, most commonly caused by retrobulbar hematoma. As pressure rises, both the optic nerve and its vascular supply are compressed, rapidly leading to nerve damage and blindness if not quickly relieved. This condition requires immediate emergency treatment to prevent permanent vision loss.
Q2: How does the lateral canthal tendon anatomy relate to orbital compartment syndrome?
The lateral and medial canthal tendons hold the eyelids firmly in place, forming an anatomical compartment with limited space for the globe. The lateral canthal tendon splits into superior and inferior crura. In OCS, elevated retrobulbar pressure forces the globe anteriorly against these tendons, requiring their surgical release to decompress the eye.
Q3: What is a Marcus Gunn pupil and how is it detected?
A Marcus Gunn pupil, or relative afferent pupillary defect (RAFD), occurs when optic nerve damage prevents normal pupil constriction. It is detected using the Swinging Flashlight Test: light directed at the unaffected eye causes both pupils to constrict, but light directed at the affected eye causes neither pupil to constrict, indicating optic nerve involvement.
Q4: How is intraocular pressure measured to confirm orbital compartment syndrome?
Intraocular pressure is measured using a handheld tonometer after topical anesthesia with tetracaine or proparacaine. The tonometer tip is pressed lightly against the cornea until the device chirps and displays a reading. Several consecutive measurements greater than 40 mm Hg confirm OCS diagnosis.
Q5: What supplies and anesthetic technique are needed for lateral canthotomy and inferior cantholysis?
Essential supplies include sterile gauze, saline, 1% lidocaine with 1:100,000 epinephrine, a 25- or 27-gauge needle syringe, toothed forceps, a straight hemostat, and iris scissors. Local anesthetic is injected laterally 1.5-2 cm, then redirected 45 degrees inferiorly while injecting continuously to anesthetize both the lateral and inferior regions.
Q6: What are the key procedural steps for performing lateral canthotomy?
After anesthesia, a hemostat is placed over the lateral canthus with approximately 2 cm of tissue between prongs. The tissue is compressed for 1-2 minutes to minimize bleeding and create a cutting guide. Using iris scissors, cut through all layers along the compressed tissue from the lateral canthus to the orbital rim, severing the lateral canthal tendon.
Q7: When is inferior cantholysis performed and what complications should be monitored?
Inferior cantholysis is performed after lateral canthotomy by retracting the lower lid and cutting the inferior crus with iris scissors directed at 90 degrees. Intraocular pressure is remeasured; if still above 40 mm Hg, the superior crus is also released. Potential complications include bleeding, infection, tissue injury, and rare globe puncture, though these risks are minimal compared to untreated vision loss.