Orbital Cellulitis: Optometry Case #32

Everything in this case turns on one anatomical line: the orbital septum. In front of it, a swollen infected lid is unpleasant but generally straightforward. Behind it, the infection is in the muscle and fat of the orbit — which is why this diagnosis is also called postseptal cellulitis — and it sits next to the optic nerve and a direct route into the skull. Three findings say the process is behind the septum, and they are the most important distinguishing features: restricted eye movement, pain on eye movement, and proptosis. He has all three. He cries when following a finger and it is the movement rather than the lid that upsets him; he cannot fully abduct or elevate; and measured rather than eyeballed, the eye protrudes 5 mm further than its fellow. Chemosis, fever and a peripheral leucocytosis all support it. Crucially, none of those three can be produced by an infection confined to the lid, because a lid infection has no mechanism to tether an extraocular muscle or push a globe forward. The history explains how it got there. He had a week of heavy upper respiratory illness with constant nasal blockage first, and in up to 86% to 98% of cases there is coexisting rhinosinusitis, with the ethmoid sinus — separated from the orbit by only a paper-thin wall — the one most likely to progress. His imaging shows exactly that: a completely opacified ethmoid and a 6 mm collection against the medial orbital wall. It is also worth noting what is absent: no injury, no scratch, no insect bite, which is the other common route to a swollen lid and would have pointed at the preseptal diagnosis instead. Two numbers govern what happens next. Vision has dropped to 20/40 from 20/20, which is a measurable threat rather than an impression, but there is no relative afferent pupillary defect, so the optic nerve is compromised rather than failing and there is time to image and treat medically. Management is empiric broad-spectrum intravenous antibiotics — vancomycin plus a cephalosporin — covering Staphylococcus aureus and Streptococcus species, for a minimum of two to three weeks. The surgical triggers are explicit and worth memorising, because this child sits just under all of them: an abscess larger than 10 mm, intracranial extension, or failure to improve within 24 to 48 hours. His collection is 6 mm with no intracranial spread, so he is admitted, treated and watched closely — and the acuity is what is being watched.