Use of herbal medicines and nutritional supplements in ocular disorders: an evidence-based review

Methodological quality of the review: Low confidence

Author: Wilkinson JT, Fraunfelder FW.

Region: Details not provided

Sector: Ocular disorders, cataract, age-related macular degeneration, diabetic retinopathy and glaucoma.

Sub-sector: Herbal medicines, nutritional supplements, complementary and alternative medicine.

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative analysis

Qualitative synthesis methods: Not applicable

Background

The use of complementary and alternative medicines (CAM), including nutritional supplements, is widespread and growing as a trend in the treatment of a range of diseases. However, randomized control trials examining the effectiveness of CAM therapies are scarce. Authors note that herbal medicines and nutritional supplements are of clinical importance to ophthalmologists because many of these therapies are promoted as beneficial for eye disease. Conversely, many herbal and vitamin supplements are also associated with systematic adverse effects that could ‘interfere with prescription medicines’. It is important for practitioners to understand the potential benefits and adverse effects of complementary and alternative medicine.

Research objectives

‘To examine the evidence regarding the use of herbal medicines and nutritional supplements in age-related macular degeneration (AMD), cataracts, diabetic retinopathy and glaucoma, and to review the ocular adverse effects of herbal and nutritional agents of clinical importance to ophthalmologists’

Main findings

The number, type and geographical location of studies included were not clearly reported in the review. All studies included assessed information on nutritional supplements and herbal medicines that are used for eye diseases as well as complications of using these agents.

Authors concluded that currently there was little evidence to recommend the use of herbal medications or antioxidants in the treatment of prevention of cataracts, glaucoma or diabetic retinopathy. There was, however, strong evidence supporting the use of antioxidants and zinc in patients with certain forms of intermediate and advanced age-related macular degeneration. There is also growing evidence of potential significant adverse effects associated with ‘AREDS’ formula vitamins.

A lot of the research to date was inconclusive and warranted further research on the association of complementary alternative medicines and ocular disorders.

Methodology

Authors included studies involving humans only written in English providing evidence level I or II. They conducted a search on Ovid MEDLINE and Ovid OLDMEDLINE (1947-2011) as well as other selected websites including the American Academy of Ophthalmology (AAO), the Centres for Disease Control and Prevention (CDC), the National Institutes of Health (NIH) and the World Health Organization (WHO).

Applicability/external validity

The authors did not discuss how generalizable the results are and no methods to assess external validity were mentioned.

Geographic focus

The number, study design and their geographical location were not fully reported in the review, although studies from the US, the Netherlands and Australia were cited in the results section.

Quality assessment

This review was attributed low confidence in the conclusions about the effects as major limitations were identified. The search was not sufficiently comprehensive; apart from selected websites only one database was searched. Language bias was not avoided and authors did not contact authors/experts for additional studies and references lists of included trials were not part of the search strategy. Therefore, we could not be confident that relevant studies were not omitted. Additionally, it was unclear if the screening of full texts was conducted independently by two reviewers, and authors did not provide details in regards to methods used to extract data of included studies.

Details of included studies including their characteristics, interventions and outcomes were not comprehensively reported. The likelihood of bias within the included studies was not addressed, neither was the external validity or generalizability of the results. Methods used to analyse the findings were in narrative form although the reasoning for adopting this methodology was not reported. The review does not address the issue of heterogeneity between the studies.