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Evidence Library

Research Library: How We Support Every Claim

We rank evidence by strength rather than treating every source as equally credible. Here's the framework we use across this site, plus every major source cited in our VisiFlora content.

Our Evidence Ladder

1

Large randomized controlled trials & government research bodies

Example: the NEI's AREDS2 trial (4,203 participants) — the strongest tier of evidence in this field.

2

Smaller randomized, placebo-controlled trials

Example: the 2020 bilberry ciliary-muscle study (109 participants) — solid evidence, smaller sample.

3

Systematic reviews & narrative reviews

Example: gut-eye axis systematic reviews — useful for mapping an emerging field, not proof of a specific product's effect.

4

Mechanistic / preclinical research

Lab and animal studies that suggest a plausible pathway but haven't been confirmed in humans at scale.

5

Unreferenced marketing claims

Treated with the most skepticism — claims like "6,000x stronger" or unverifiable celebrity/institutional endorsements fall here, and we flag them explicitly rather than repeating them.

Full Source List

  1. National Eye Institute. "About AREDS and AREDS2." nei.nih.gov
  2. Chew EY, et al. "Secondary analyses of the effects of lutein/zeaxanthin on AMD progression: AREDS2 report No. 3." JAMA Ophthalmol. PubMed 24310343
  3. Kosehira M, Machida N, Kitaichi N. "A 12-Week-Long Intake of Bilberry Extract Improved Objective Findings of Ciliary Muscle Contraction of the Eye." Nutrients, 2020. PMC7146147
  4. Chung HS, et al. "Ginkgo biloba Extract Increases Ocular Blood Flow Velocity." J Ocul Pharmacol Ther, 1999. PubMed 10385132
  5. Wimpissinger B, et al. "Influence of Ginkgo biloba on ocular blood flow." Acta Ophthalmol Scand, 2007. PubMed 17324220
  6. "Ginkgo biloba and its potential role in glaucoma." PubMed. PubMed 29206653
  7. "Clinical trials targeting the gut-microbiome to effect ocular health: a systematic review." PubMed, 2023. PubMed 36918627
  8. "From Gut to Eye: Exploring the Role of Microbiome Imbalance in Ocular Diseases." PubMed, 2024. PubMed 39337098
  9. "Targeting the Gut–Eye Axis: An Emerging Strategy to Face Ocular Diseases." PMC, 2023. PMC10488056
  10. "Effect of astaxanthin- and tocotrienol-containing foods on ocular function." ScienceDirect. ScienceDirect

Every claim on this site that references a specific study links back to one of these sources, or is explicitly flagged as unverified marketing language when it can't be independently confirmed. See our Content Standards page for our full methodology.