Non-traumatic diplopia as a rare complication following functional endoscopic sinus surgery—case report

Functional endoscopic sinus surgery (FESS) is performed for the management of medically refractory chronic rhinosinusitis (CRS). Given the vascularity of the nasal cavity, controlled hypotension is often employed to improve the intra-operative surgical field. Diplopia is a rare complication following FESS, and the most feared aetiology is either orbital trauma and/or injury to extraocular muscles. However, non-traumatic causes of diplopia can also occur coincidentally following FESS. Herein, we present two rare cases of delayed onset diplopia after FESS (range of onset from 10 to 30 days). There was no history of intra-operative orbital injury and nil evidence of orbital trauma on post-operative imaging. Case 1 had a history of hypertension and atrial fibrillation, while Case 2 did not have any vascular risk factors. The intraoperative systolic blood pressure during sinus surgery ranged from 80–95 and 85–110 mmHg. Case 1 was diagnosed with a decompensating esotropia (underlying strabismus) which was treated with prism glasses. Case 2 had a microvascular abducens nerve palsy that resolved after 3 months. This case study illustrates that, in the absence of orbital or extraocular muscle trauma during surgery, alternative diagnoses such as an underlying strabismus or microvascular cranial nerve palsy can be included in the differential diagnosis.