To determine whether magnesium sulphate could induce controlled hypotension, reduce choroidal blood flow, provide a ‘dry’ operative field and could be compared with sodium nitroprusside in the recently raised issue of the use of hypotensive anaesthesia in eye surgery, i.e. for choroidal tumour surgery as the choroid is the most fragile and vascular structure in the eye.

Forty adult patients undergoing choroidal melanoma resection and anaesthetized with 2.5 mg kg−1 propofol, followed by a constant infusion of 120 μg kg−1 min−1, and remifentanil 1 μg kg−1, followed by a continuous infusion of 0.25 μg kg−1 min−1, were randomly assigned to two groups to receive either magnesium sulphate or sodium nitroprusside.

Controlled hypotension was achieved at the target systolic pressure of 80 mmHg within 107 ± 16 and 69 ± 4.4 s for magnesium sulphate and sodium nitroprusside, respectively. Choroidal blood flow decreased by 24 ± 0.3% and 22 ± 3.3% for magnesium sulphate and sodium nitroprusside, respectively. Controlled hypotension was sustained in both groups throughout surgery, and the surgical field rating decreased in a range of 80% in both groups. Sodium nitroprusside decreased pH and increased PaCO2. There were no postoperative complications in any of the groups.

Magnesium sulphate controlled hypotension, reduced intraoperative pressure and provided good surgical conditions for choroidal melanoma resection with no need for additional use of a potent hypotensive agent in adults.