Post-operative visual loss: An unusual complication after exploratory laparotomy.

Sir,

Post-operative visual loss (POVL) is an unexpected, unusual and devastating complication, sometimes seen after cardiac, spine and head neck surgery. Although the exact pathological mechanism is obscure in most cases it occurs because of ischemia to visual pathways. We present a rare case of POVL involving non-cardiac, non-neurological surgery in a 15-year-old boy after exploratory laparotomy for acute abdomen.

On admission he was moderately dehydrated, his BP was 80/55 mmHg, pulse rate was 112/min, respiratory rate was 24/min. He was afebrile with normal cardio-respiratory examination. Baseline laboratory investigations were within normal range except Hb level of 10 gm/dl. Ultrasound of abdomen showed intussusceptions of bowel loops. The patient was taken up for surgery after fluid resuscitation with baseline pulse rate 93/min, BP 110/70, ECG was normal and SpO2 was 98% on air. General anaesthesia with endotracheal intubation using thiopentone sodium, atracurium, fentanyl and isoflurane was used. Sixty minutes of intra-operative period was uneventful except one episode of hypotension (BP-77/54 mmHg) which responded to IV fluids and he received one unit of fresh blood. The patient was shifted to PACU after extubation of trachea with stable vitals. Few hours later when fully conscious, the nurse noticed that the patient was behaving abnormally, was agitated and confused. On interrogation, he complained that he was unable to see anything. Ophthalmic examination showed normal sized pupils, with normal papillary responses to light and no restriction of eyeball movement. Fundus examination was normal. Neurological examination was also normal. MRI imaging of brain showed signal intensity abnormality with bilateral ischemic areas in occipital lobes [Figure 1]. He was diagnosed as a case of post-operative cortical blindness. As this is a self limiting complication, he was reassured and kept on strict vigilance. The vision improved over 6-7 days.

Figure 1

MRI imaging of brain showed signal intensity abnormality in bilateral occipital lobes bilateral ischemic areas in occipital lobes

Post-operative visual loss after non-ophthalmic surgery is a rare event with the incidence ranging between 1 in 61,000 to 1 in 1,25,000 operations but following spinal surgery in prone position, is estimated to be 1 in 1,100. Incidence is also high after cardiac bypass and head neck surgery.[12]

Visual loss can be caused by damage to any connecting striate area between cornea and occipital cortex. The three main causes are ischemic optic neuropathy (ION), central retinal artery thrombosis (CRAT) and cortical blindness (CB). Of these ION is commonest in patients above 50 years of age undergoing cardiothoracic or spinal surgery.[34] Possible causes include severe hypotension, blood loss, anaemia and haemodilution. CRAT causing retinal ischemia due to central or branch retinal artery occlusion may occur due to external pressure on eyeball, as seen following prolonged and faulty prone position during spine surgery. Cortical blindness (CB) occurs due to brain injury rostral to optic nerve as a result of ischaemic stroke to occipital cortex. Exact pathological mechanism of CB is unknown, although some factors have been suspected such as prolonged and profound hypotension, embolism, spasm or thrombosis.[5] Occipital region of brain is a watershed zone for the middle and posterior cerebral arteries and may undergo infarction during periods of hypotension.[5] It may be associated with brief period of encephalopathy and is extremely rare after non-cardiac and non-neurological surgery. The cause of CB in our patient is uncertain. Most likely cause could be perioperative hypotension. CB due to hypotension has good prognosis with rapid recovery in most cases. However, this complication should be differentiated from embolic or vaso-occlusive causes which may have similar presentation but might require anti-coagulants or thrombectomy.