Postoperative blindness – a rare but devastating complication

Abstract

EDITOR: Postoperative visual loss (POVL) is one of the most unexpected complications after surgery with an estimated incidence varying from 0.01 to 1% depending on the type of surgery [1-4]. Although POVL is observed after almost any type of surgery 67% and 10% of all reported cases occur after prone spine procedures and cardiopulmonary bypass cases, respectively [2,4]. The most common cause associated with POVL (81%) is ischaemic optic neuropathy (ION) of the anterior (AION) or posterior (PION) part of the optic nerve [3,5]; only 6% of POVL cases were diagnosed as central retinal artery occlusion (CRAO). ION results from an ischaemic insult of the optic nerve characterized by oedema or pallor around the optic nerve and is often associated with a decrease in pupillary response [1,6]. Clinically ION is manifested by an unilateral or bilateral acute/subacute loss of vision or visual acuity hours to days after surgery. The descriptions of the visual deficits range from transient blurred vision to total blindness on one or both eyes [3]. Although various therapy strategies or interventions including high-dose steroids, mannitol, hyperbaric oxygen and furosemide were attempted no treatment has proven efficacy [5]. Prognosis for complete recovery from ION is poor and patients are frequently left with extensive visual impairment. Because of the lack of a beneficial treatment for ION and the poor prognosis prevention of POVL is important. Suggested preoperative risk factors include hypertension, diabetes, polycythaemia, smoking, renal failure, narrow-angle glaucoma, atherosclerotic vascular disease, collagen vascular disorders and variations in ocular anatomy or physiology. Furthermore, numerous intraoperative risk factors include prolonged prone positioning, hypotension, large blood loss, anaemia, extensive fluid administration and vasoactive drugs [1,2,5,6]. However, there is no experimental or clinical evidence that the proposed risk factors are causally linked to the occurrence of POVL. Thus, there exist currently no evidence based prevention strategies. This treatment dilemma, the incomplete knowledge about the etiology of ION and an increased incidence of POVL has led the American Society of Anesthesiologists (ASA) Committee on Professional Liability to develop the ‘ASA Postoperative Visual Loss Registry’ in July 1999. Aim of the ASA registry is to collect detailed information about POVL cases, determine possible risk factors for POVL and improve our understanding about the etiology of POVL. Currently 129 (June 2005) cases of POVL have been submitted to the ASA Registry [3]. In a preliminary evaluation of 113 POVL cases reported to the ASA Registry 71 occurred in middle-aged patients (median 50 yr) undergoing spine surgery and were caused by ION [3]. In more than 90% anaesthetic duration was <6 h and in 85% the estimated blood loss was >1 L. 9 cases of CRAO had significantly lower mean anaesthetic duration and estimated blood loss compared to ION cases. Importantly 14 patients with ION had their heads placed in Mayfield pins with their eyes free from external pressure indicating that isolated ION is not caused by pressure on the globe [3]. Recently, the American Society of Anesthesiologists Task Force on Perioperative Blindness issued a practice advisory for perioperative visual loss associated with spine surgery [7]. In summary, POVL is a rare and disastrous complication particularly associated with spine and cardiac surgery. Several suggested but not proven risk factors include intraoperative hypotension, anaemia and large blood losses or prolonged prone position indicating a multifactorial etiology of POVL. Until now, there are no evidence-based treatment or prevention strategies available. What can we do as an anesthesiologist about POVL? Apparently there is an urgent need for all anaesthesiologists to closely follow literature and gain knowledge about POVL; the brief booklet about POVL for anaesthesiologists available on the ASA closed claims webpage offers a good summary of this phenomenon [8]. We should be aware that patients undergoing prolonged prone spinal surgery and cardiopulmonary bypass surgery with hypotension and anaemia may have an increased risk of postoperative visual loss secondary to ischaemic optic neuropathy. Patients with POVL should be evaluated by an ophthalmologist as quickly as possible; a gross exam (e.g., reading letter or counting fingers) does certainly not rule out scotoma or delicate visual field deficits as it occurs in ION. Finally, every anaesthesiologist is highly encouraged to report any case of POVL following non-ophthalmic surgery to the ASA POVL Registry (www.asaclosedclaims.org). Further research is needed to improve our understanding about the etiology of POVL, to determine risk factors and to clarify the mechanisms of ION. Recently developed animal models for ION may hopefully improve our knowledge about the mechanisms of ION and offer the possibility to develop appropriate treatment strategies [9].