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

The CSV trial is designed to evaluate the effect of oral carotenoid supplementation on contrast sensitivity in Chinese adults, addressing a gap in research previously conducted primarily in European populations.

• Previous research has demonstrated that oral carotenoid supplementation can enhance contrast sensitivity in European populations.
• The study aims to determine whether similar benefits apply to the Chinese population.
• The trial is conducted at the Zhongshan Ophthalmic Center in Guangzhou, China.
• The study specifically targets adults free of retinal disease.

The trial will randomise 220 eligible Chinese adults in a 1:1 ratio to receive either an active carotenoid supplement or a placebo.

• 220 eligible Chinese adults will be randomised in a 1:1 ratio (110 per group).
• The active supplement contains 10 mg lutein, 10 mg meso-zeaxanthin, and 2 mg zeaxanthin in a formula-based oil suspension administered as one soft gel capsule.
• The placebo consists of an oil soft gel capsule.
• The intervention duration is 1 year.
• The trial is double-blind and placebo-controlled.

The primary outcome of the CSV trial is change in contrast sensitivity at 6 cycles per degree (cpd) over the 1-year study intervention.

• The primary outcome assesses change in contrast sensitivity at 6 cpd over 1 year.
• Secondary outcomes include contrast sensitivity at 6 cpd at 3-month and 6-month follow-ups.
• Additional secondary outcomes include contrast sensitivity at other cpd, best-corrected visual acuity (BCVA), subjective visual function, and skin carotenoid levels.
• Assessments occur at baseline and at 3-month, 6-month, and 12-month follow-up visits.

Participants will undergo a comprehensive set of ophthalmological and biochemical assessments at multiple time points throughout the trial.

• Ophthalmological procedures include best-corrected visual acuity, contrast sensitivity, optical coherence tomography, fundus photography, and skin carotenoid examinations.
• These examinations are conducted at baseline and at 3-month, 6-month, and 12-month follow-up visits.
• Blood tests and a Dietary Carotenoid Screening Questionnaire are administered at baseline and at the 12-month follow-up.
• Subjective visual function questionnaire interviews are administered at baseline and at the 3-month, 6-month, and 12-month follow-ups.

The CSV trial received ethics approval from the Ethics Committee of the Zhongshan Ophthalmic Center and is registered as a clinical trial.

• The trial was approved under Ethics Committee reference No. KYPJ141-4.
• The trial is registered under ClinicalTrials.gov identifier NCT06098677.
• Written informed consent will be obtained from all participants prior to their involvement.
• Results will be disseminated through peer-reviewed publication and conference presentations.