Andy C. O. Cheng
Dr. Andy Cheng graduated from the Medical Faculty of the University of Hong Kong with honors and further attained the Master of Medical Science degree with distinction in HKU specializing in morphological science and neuroscience. He holds the Diploma in Practical Dermatology qualification from the Cardiff University. He is currently the Fellow of the Royal College of Surgeons of Edinburgh, College of Ophthalmologists of Hong Kong, and Hong Kong Academy of Medicine. Dr. Cheng is the Honorary Consultant Ophthalmologist of the Hong Kong Sanatorium & Hospital and the Honorary Clinical Assistant Professor of the Chinese University of Hong Kong. He has subspecialties interest in orbit & oculoplastic surgery and neuro-ophthalmology..
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Perioperative visual loss (PVL) has been described in many types of surgery. The risk of PVL after any surgery in general was estimated to be about 0.002 % . Not surprisingly, the risk of PVL is highest among patients undergoing cardiac, spinal or ophthalmic/neurologic surgeries, risk estimated to be about 0.086 %, 0.03 % and 0.05 %, respectively [1–3].
For most non-ophthalmic procedures, the face-down positioning (especially for spinal and neurosurgical procedures) has long been blamed as one of major causes for the visual loss, partly explained by the unintentional pressure over the periorbital region by the headrest in some cases, while some believe that compromise of orbital circulation due to raise in intra-orbital pressure caused by prone positioning itself may be a more important factor .
Visual loss after non-ocular ophthalmic procedures encompasses mainly orbital and eyelid surgeries. Though rare, it can result in major sequelae to both the patients and surgeons. A few studies have attempted to elucidate the incidence, aetiology, clinical course and optimal management of this devastating complication [4–7]. However, due to its rarity, different inclusion criteria and definition of visual loss used in various studies, this condition still remains not fully understood and unfamiliar to some practitioners.
Visual Loss After Orbital Surgery
The incidence of visual loss after orbital surgery in general was estimated to be about 0.44–0.6 % [4, 5]. In the study by Bonavolonta, which was one of the early studies on the incidence of visual loss after orbital surgery, all patients with pre-operative visual acuity of <20/40 were excluded . This may theoretically excluded those higher risk cases for visual loss, which resulted in a lower estimated risk of 0.44 % . Moreover, the definition of visual loss was not standardized in various studies, which made comparison between studies not meaningful.
On the other hand, different procedures on different locations carry different risk. Orbital decompression was found to carry a lower risk of visual loss comparing to orbital exploration for tumour removal or biopsy . In the study by Rose published in 2007, there was no case of visual loss after 1350 orbital decompression, whereas there were 14 cases of visual loss in 1150 orbital exploration (1.2 %) .
Two major mechanisms were postulated to be the major causes of the post-operative visual loss after orbital surgery, namely, ischaemic optic neuropathy and retinal artery occlusion due to vasospasm [4, 5]. Manipulation around the posterior part of intra-orbital optic nerve is of particular risk since this part of the optic nerve has a sole blood supply from the perforating dural vessels . Interruption of the blood supply due to vasospasm may cause irreversible ischaemic optic neuropathy, depending of the duration of ischaemia.
With the knowledge of the possible pathophysiology for visual loss after orbital surgery, it is not surprising that certain disease condition and patient characteristics carry a higher theoretical risk of post-operative visual loss.
It is thought that larger lesions, intraconal lesions, especially located around the orbital apex, and lesions that are in contact with/alongside the optic nerve or even displacing the middle and/or posterior third of the optic nerve are of higher risk . The highest risk lesions are those “peanut” lesions wedged in the orbital apex and massive vascular malformations  (Fig. 21.1a, b). This may be related to the need for additional surgical manipulation around the optic nerve, which may induce reversible vasospasm of the perforating dural vessels or even transecting the vessels. Excessive bleeding (with free blood and inflammatory mediators) and use of bipolar cautery may also induce the vasospasm . The former may also lead to an intraoperative “steal syndrome” compromising the blood supply to the optic nerve .