Can sunlight and ribodlavin (vitamin B2) treat keratoconus? ELZA asks questions…
A recent publication in the Revista Brasileira de Oftalmologia addresses a question that is increasingly circulating online and among patients: whether keratoconus can be treated using high-dose oral riboflavin (vitamin B2) combined with sunlight exposure.
The article is a Letter to the Editor responding to a previously published study that suggested such an approach “appears to be effective in stabilizing the progression of keratoconus.”
It was authored by a team from the ELZA Institute in Zurich, including Dr. Emilio A. Torres-Netto, MD, PhD, FEBO, FWCRS and Farhad Hafezi, MD, PhD, FARVO e Dr. Mark Hillen, PhD, who questioned some of the assumptions in the original paper the letter asks questions about.
The original article can be accessed aqui:
What was being claimed
The original study proposed that combining oral riboflavin with sunlight exposure may stabilise keratoconus, in effect performing reticulação da córnea. This idea has gained attention because it appears simple and accessible, particularly compared to clinical cross-linking procedures.
Limitations of the study design
The response highlights that the study was retrospective, uncontrolled, and involved a relatively small number of patients, with attrition over a short follow-up period. Crucially, there was no requirement that keratoconus was actively progressing at baseline.
In this context, observed stability cannot be interpreted as a treatment effect. As the authors state, “these are not minor limitations, but fundamental barriers to establishing causal efficacy.”
Confounding factors
The interpretation is further complicated by additional measures applied during the study. Patients were instructed to avoid eye rubbing and received anti-allergic therapy. Both are known to reduce keratoconus progression independently.
These effects were not separated from the proposed influence of riboflavin and sunlight, making it difficult to attribute any observed changes to the intervention itself.
Biological plausibility of sunlight riboflavin keratoconus treatment
Reticulação da córnea depends on achieving sufficient riboflavin concentration within the cornea and delivering a defined amount of ultraviolet energy.
The authors report that systemic riboflavin produces stromal concentrations “more than 400-fold lower than the concentration typically achieved with topical instillation in clinical CXL.”
At the same time, the ultraviolet exposure from sunlight is far lower than that used in clinical protocols, with absorbed energy “three orders of magnitude below that delivered in the Dresden protocol.”
Under these conditions, the requirements for effective cross-linking are not met.
Experimental evidence
The publication refers to controlled experimental data in which oral riboflavin and sunlight exposure did not increase corneal stiffness. Biomechanical testing showed no strengthening effect, and some findings were consistent with reduced stiffness.
These results directly contradict the expected outcome of successful cross-linking.
Variability of sunlight exposure
Natural sunlight is inherently variable. Exposure depends on geographic location, time of day, season, weather conditions, and individual behaviour.
Without precise measurement of ultraviolet dose, it is not possible to standardise treatment or reliably attribute any observed effects to a photochemical process. The authors describe such attribution as speculative.
Clinical implications
The authors raise concern that promoting this approach could delay access to proven treatment. Corneal cross-linking performed in a clinical setting remains the only intervention with established efficacy in halting keratoconus progression.
As noted in the publication, “the potential for harm is considerable if patients forego timely CXL based on unsupported claims.”
Conclusão
This publication does not support the concept of sunlight-activated cross-linking using oral riboflavin. Instead, it provides a structured critique of the available evidence and explains why the proposed mechanism is unlikely to produce a clinically meaningful effect.
For patients, the key message is that corneal cross-linking performed under controlled clinical conditions remains the standard of care for stopping keratoconus progression.
Referências
Almodin EM, Almodin F, Almodin J. Corneal collagen cross-linking by sun exposure and high dose oral riboflavin: a multicentric longitudinal observational study. Revista Brasileira de Oftalmologia. 2025;84:e0036.
Torres EA, Aydemir ME, Lu NJ, et al. Letter to: Corneal collagen cross-linking by sun exposure and high dose oral riboflavin: a multicentric longitudinal observational study. Revista Brasileira de Oftalmologia. 2026;85:e0020.
