Although POVL in prone position following spinal surgery is rare, this complication is a disaster, which might be irreversible and seriously reduce quality of life. In 2016 Epstein and colleague [3] reviewed 20 cases of blindness with spine surgery, unexpectedly 8 patients were permanent visual loss postoperatively. Consequently it has to be paid more attention on this complication. In 2012, Quraishi [7] reported a patient lost bilateral eyesight following lumbar surgery in prone position, whose VA resolved within 48 hours. The case might be the shortest visual loss since recording. However the patient of this case resolved within 5 hours, and follow-up ophthalmic examination confirmed his VA recovered to 0.3 in the affected eye. So this was a luck case with the fastest recovery.
Visual loss after spine surgery under GA in prone position has gained more and more recognition recently. In American, this incidence was the second among the POVL of nonocular operations [8]. ION is the most frequently cited cause of POVL under GA [9]. No less than 89% of all POVL is attributed to ION, which including anterior ION and posterior ION depending on the location of lesion [3, 5]. Because of reduced light reflex and edematous retinal, CRAO was suspected firstly leading to ION.
There are multiple risk factors developing POVL in prone position. However, the patient in this case did not possess these recognized or suspected risk factors, for example, obesity, prolonged operative times, diabetes, and so on [3]. During the operation, his hemodynamic was tightly controlled and maintained stably without greater blood loss. Meanwhile, his head was secured without any pressure on the globe and positioned correctly in a neutral prone position without cervical rotation. And his head was maintained in a neutral forward position higher than the heart during the operation.
There might be other possible risk factors in this patient, for instance, he was a male. Male gender has been known as a risk factor relative to POVL [1, 8]. Meanwhile, he was positioned in prone position, which might increase direct pressure on the abdomen and obstructed venous return to heart. Obstruction of venous returning increases central venous pressure, further raises intraocular pressure. This is another recognized risk factor of POVL [2, 7]. The patient lost about 10 ml blood and 100 ml urine, fluid input was about 1600 ml crystalloid intraoperatively. Although the fluid volume was not large, there was lack of colloid. Intraoperative crystalloid overload contributes to the optic nerve perfusion pressure reduction, which is also considered to result in POVL [10]. The volume of 1600 ml crystalloid might not be overload for a 78 kg male patient, we merely speculated the shortage of colloid might be a criminal cause.
On the other hand, 1600 ml crystalloid was actually considered obvious shortage for a 78 kg male patient because of his preoperative fasting more than 10 hours. It might cause hypercoagulability which is a risk factor to develop CRAO [11]. Therefore, various treatments of anticoagulation, vasodilation and adequate fluid infusion were combined.
As well-known, although muscarinic agonist can produce intact blood vessels dilation in various species [12], this vasorelaxation only occurs in normal blood vessels. For abnormal blood vessels, muscarinic agonist might cause paradoxical vasoconstriction [13]. Thus based on the previous clinical experience, the patient was administered with atropine peribulbar injection which might relieve spasmodic retinal artery [14].
The patient was also treated with high flow oxygen inspiration and hyperbaric oxygen immediately after CRAO diagnosis. In patients with CRAO, oxygen therapy showed beneficial effects, especially when 100% oxygen and hyperbartic oxygen were administrated, which were proved to improve VA in CRAO patients significantly [15]. As an efficacious, well-tolerated and few-side-effects therapeutic method, hyperbaric oxygen can be used in treatment of acute and subacute CRAO patients, but also it is recommended as emergent therapeutic option [16–18]. We firmly believed these combined therapies to produce the benign clinical outcome.
There were no obvious risk factors in this patient, however, he did suffered transient unilateral POVL. There must be some etiologies we did not detect, which worked together to lead to POVL in prone position. Most cases of POVL were irreversible, this case was very lucky because his VA recovered beginning at postoperative 5 hours, and further ophthalmic consultation confirmed his VA of the affected eye was better and better. This is the fastest recovery of POVL in prone position after spine surgery in Pubmed and PMC recording. No doubt these immediate diagnosis and treatments were important to the benign clinical prognosis. However, it is critical to learn and recognize these etiologies and risk factors to avoid POVL in prone surgery. The best method avoiding POVL is to prevent it [19].
Therefore, POVL need to be considered as one of severe complications in prone spine surgery, which has to be emphasized. There are many perioperatve risk factors causing POVL, thus preoperative counseling, intraoperative strictly monitoring, correct position and stable hemodynamic, and postoperative follow up are essential.