Effect of carotenoids supplementation on visual function in Chinese adults free of retinal disease: protocol for the CSV double-blind, randomised, placebo-controlled trial

Introduction The macula is a pigmented area located at the centre of the retina, responsible for central, high-resolution colour vision. Previous research has demonstrated that oral carotenoid supplementation can enhance contrast sensitivity (CS) in European populations. This study aims to investigate whether carotenoid supplementation can also improve visual function in the Chinese population.Methods and analysis The Contrast Sensitivity Vision (CSV) trial is a double-blind, randomised controlled trial conducted at the Zhongshan Ophthalmic Center in Guangzhou, China. 220 eligible Chinese adults will be randomised in a 1:1 ratio to receive either oral supplementation of 10 mg lutein, 10 mg meso-zeaxanthin and 2 mg zeaxanthin in a formula-based oil suspension (administered as one soft gel capsule) or a placebo oil soft gel capsule daily for 1 year. Participants in both groups will undergo ophthalmological study procedures including best-corrected visual acuity (BCVA), contrast sensitivity, optical coherence tomography, fundus photography and skin carotenoid examinations at baseline and at 3-month, 6-month and 12-month follow-up visits. Blood tests and a Dietary Carotenoid Screening Questionnaire will be administered at baseline and at the 12-month follow-up. Subjective visual function questionnaire interviews will be administered at baseline and at the 3-month, 6-month and 12-month follow-ups. The primary outcome will assess change in CS at 6 cycles per degree (cpd) over the 1-year study intervention. Secondary outcomes will examine CS at 6 cpd at the 3-month and 6-month follow-up, CS at other cpd, BCVA, subjective visual function and skin carotenoid levels as measured at baseline, 3-month, 6-month and 12-month follow-ups.Ethics and dissemination The CSV trial was approved by the Ethics Committee of the Zhongshan Ophthalmic Center, Guangzhou, China (No. KYPJ141-4). Participants will have the opportunity to ask questions about the trial, and written informed consent will be obtained from all participants prior to their involvement in the study. Results will be disseminated through peer-reviewed publication and conference presentations.Trial registration number NCT06098677.