The reduction of LEDD leads to visual dysfunction in patients with PD after STN-DBS: a randomized clinical trial

Medication adjustment after deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson's disease (PD) may influence visual function. However, no clinical trials have been designed specifically to investigate this effect.

To compare the effects of levodopa-equivalent daily dose (LEDD) reduction and non-reduction on visual function in patients with Parkinson's disease (PD) following STN-DBS.

This was a multi-center, prospective, randomized, double-blinded clinical trial. A total of 208 patients with Parkinson's disease were referred for DBS between June 2019 and July 2021 and analyzed between June 2023 and July 2023. STN-DBS was performed, and the LEDD was reduced in one study arm but not in the other. The primary outcome measure was visual impairment in Parkinson's disease questionnaire (VIPD-Q) with or without LEDD reduction 12 months postoperatively, and the secondary outcomes included retinal nerve fiber layer (RNFL) thickness, vessel density, eye-tracking system results, contrast sensitivity and visual field.

During the short-term follow-up, DBS implantation and stimulation did not significantly affect visual function (VIPD-Q, baseline vs. 1 month, 9.269±8.385 vs. 8.938±7.666, Mann-Whitney U tests; P=0.6746). In the long-term follow-up, the reduction group demonstrated a significant decline in visual function, RNFL thickness, and vessel density after STN-DBS compared with the control group without STN-DBS (P<0.001).

Visual dysfunction, particularly a thinner RNFL and lower vessel density, is related to LEDD reduction after STN-DBS. Prolonged administration of dopamine-mimetic drugs prevents visual symptoms. Thus, physicians should consider LEDD adjustment when patients report visual dysfunction before surgery or severe visual symptoms after STN-DBS.