Case #041

Every red swollen eyelid forces the same question, and the answer decides between an oral antibiotic at home and an emergency admission: is the infection in front of the orbital septum or behind it. Preseptal cellulitis stops at the lid. The eye moves fully and painlessly, acuity is normal, the pupil reacts normally and the globe sits where it should. This boy has the opposite of all four. Pain on movement, restricted movement with diplopia, a globe pushed forwards, and reduced acuity are the findings that place the infection behind the septum, and any one of them mandates imaging. The route in is anatomical. The ethmoid sinuses sit directly medial to the orbit, separated only by the lamina papyracea, a plate of bone thin enough to be named for paper, so a week of ethmoid sinusitis in a child is the commonest origin of exactly this. What raises the urgency further is the optic nerve. A relative afferent pupillary defect with desaturated colour vision and falling acuity means the nerve is being compressed by the collection, and colour vision usually fails before acuity does, which is why the plates are worth doing. Untreated, infection here spreads backwards through valveless orbital veins into the cavernous sinus, or intracranially, and blindness can follow within a day. Admission and intravenous broad-spectrum antibiotics start at once, covering staphylococci, streptococci and the anaerobes that come with a sinus source, and given intravenously rather than orally because the orbit is a closed compartment that oral therapy penetrates poorly. Drainage is not optional here: there is a rim-enhancing collection, and the failing acuity, desaturated colour vision and afferent pupillary defect say the nerve is already being compressed. Vision and eye movements are then rechecked every few hours through the first day, with imaging repeated if anything worsens.