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Effects of Omega-3 Fatty Acids on Eye Health
Evidence Reports/Technology Assessments, No. 117
Investigators: William Hodge, MD, David Barnes, MD, Howard M Schachter, PhD, Yi Pan, MSc, Elizabeth C Lowcock, BScH, Li Zhang, MLIS, Margaret Sampson, MLIS, Andra Morrison, BSc, Khai Tran, PhD, Maia Miguelez, PhD, and Gabriela Lewin, MD.
Structured Abstract
Context:
In the United States, blindness or low vision affects 3.3 million people over the age of 40, or one in 28 people in that age group. With the number of people aged 50 years or older expected to increase in upcoming decades, this number is expected to increase to 5.5 million Americans or 76 million people worldwide by the year 2020. The most important cause of low vision worldwide is cataracts; in developed countries, age related macular degeneration is the most common cause of low vision. The brain and eye are highly enriched with omega-3 fatty acids, which accumulate in these tissues during late fetal and early neonatal life. Some studies in preterm and term human infants have suggested that a dietary supply of omega-3 fatty acids is essential for optimal visual development. Several basic science studies support the hypothesis that omega-3 fatty acids may be useful therapeutic agents for pathologies of the retina and lens.
Objectives:
The purpose of this study was to conduct a systematic review of the scientific-medical literature to identify, appraise and synthesize the evidence for the effects of omega-3 fatty acids on eye health. Questions assessed the possible primary or secondary preventive influence of the intake of omega-3 fatty acids on important eye health-related outcomes. These included age-related macular degeneration (ARMD), diabetic retinopathy, retinitis pigmentosa, cataracts, and occlusions of either retinal veins or retinal arteries. Adverse effects associated with omega-3 fatty acid supplementation in interventional studies of eye health were also sought.
Data Sources:
A comprehensive search was undertaken in six databases (MEDLINE®, PreMEDLINE®, EMBASE, Cochrane Central Register of Controlled Trials, CAB Health, and Dissertation Abstracts). Searches were not restricted by language of publication, publication type, or study design except with the MeSH® term “dietary fats,” which was limited by study design to increase its specificity. Search terms related to omega-3 fatty acids and eye health. Additional published or unpublished literature was sought through manual searches of reference lists of included studies and key review articles, and from the files of content experts.
Study Selection:
Studies were considered relevant if they described live human populations of any age, involved any type of study design, and investigated the intake of any foods or extracts, known to contain omega-3 fatty acids, for their possible primary or secondary preventive influence on eye health. Ineligible were studies, which included populations exclusively exhibiting a possible or requisite subset of the symptoms or signs of eye disease/visual impairment (e.g., blurred vision). A review-pertinent diagnosis, as well as at least one review-relevant clinical ocular outcome, was required.
Data Extraction:
Two levels of screening for relevance, and two reviewers per level, were employed (bibliographic records, then full articles). Calibration exercises preceded each step of the screening process. Excluded studies were noted as to the reason for their ineligibility using a modified QUOROM format. Disagreements were resolved by forced consensus and, if necessary, third party intervention. A Technical Expert Panel (TEP) consisting of six members was convened to provide advisory support to the project. They contributed to refining the questions and highlighting key variables requiring consideration in the review. Each included study was assessed for its quality as well as its applicability to the North American population.
Data Synthesis:
Sixteen studies, described in 16 published journal articles, were found to investigate nine of 23 potential questions. Question-specific qualitative syntheses of the evidence were derived. Greater interpretative emphasis was placed on evidence from randomized controlled trials (RCTs) and other designs that were both prospective and controlled. Too little, or flawed, available evidence precluded meta-analysis for each question.
Conclusions:
Based on the studies identified by this review, clinical research has only scratched the surface with respect to understanding the possible utility of the intake of omega-3 fatty acids as a primary or secondary prevention in eye health. Moreover, seen from the point of view of clinical research’s typical, linear arc—which moves from basic science to observational research to RCTs, and culminating in the systematic review/meta-analysis of the observations obtained by these primary studies—there is a paucity of solid observational research with which to construct an experimental framework affording the meaningful conduct of RCTs. For example, there is little understanding of the exact sources, types and doses of omega-3 fatty acids, or even the possible duration of their use, which might usefully serve as definitions of a prevention-centered “intervention” for any of the eye diseases/visual impairments examined in our review. Perhaps only with respect to the question of preventing the development/progression of advanced ARMD is there some suggestive evidence, which is underscored by it being a strong public health problem, to allow researchers to consider conducting an RCT. At the same time, a single study reporting adverse event data likely does not permit laying to rest all possible concerns regarding the short- or long-term safety of omega-3 fatty acid interventions. It is therefore our view that much more research will need to be conducted before anything conclusive can be asserted with respect to the effects of omega-3 fatty acids on eye health. It is also our understanding that sorting out the possible benefits of the intake of omega-3 fatty acids in eye health might profit from taking into consideration the impact of the concurrent intake of omega-6 fatty acids and, by definition, the omega-6/omega-3 fatty acid intake ratio.
Contents
- Preface
- Acknowledgments
- 1. Introduction
- Metabolism and Biological Effects of Essential Fatty Acids
- Metabolic Pathways of Omega-3 and Omega-6 Fatty Acids
- U.S. Population Intake of Omega-3 Fatty Acids
- Dietary Sources of Omega-3 Fatty Acids
- Eye Health: An Increasingly Important Public Health Issue
- Economic Burden of Visual Impairment
- Vascular Diseases of the Retina
- Degenerative Retinal Diseases
- Cataracts
- Omega-3 Fatty Acids and the Eye
- 2. Methods
- 3. Results
- Results of Literature Search
- Report and Study Design Characteristics of Included Studies
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Preventing Age-related Macular Degeneration?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Slowing the Progression of Age-related Macular Degeneration?
- What is the Evidence that Omega-3 Fatty Acids Decrease the Rate of Progression to Advanced Forms of Age-related Macular Degeneration?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Slowing the Progression of Retinitis Pigmentosa?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Slowing the Progression of Proliferative Retinopathy in Patients with Diabetic Retinopathy?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Slowing the Progression of Clinically Significant Macular Edema in Patients with Diabetic Retinopathy?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Preventing Age-related Cataracts?
- What is the Evidence for Efficacy of Omega-3 Fatty Acids in Slowing the Rate of Progression of Age-related Cataracts?
- What is the Evidence for the Risk of Short and Longterm Adverse Events Related to the Intake of Omega-3 Fatty Acids?
- 4. Discussion
- Summary Matrix
- Summary Table
- Abbreviations
- Appendixes
- References and Included Studies
- Listing of Excluded Studies at Level 2 Screening
- Listing of Included Studies for Evidence Tables
Prepared for: Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services.1 Contract No. 290-02-0021. Prepared by: University of Ottawa Evidence-based Practice Center at The University of Ottawa, Ottawa, Canada.
Suggested citation:
Hodge W, Barnes D, Schachter H, Pan Y, Lowcock E, Zhang L, Sampson M, Morrison A, Tran K, Miguelez M, Lewin G. Effects of Omega-3 Fatty Acids on Eye Health. Evidence Report/Technology Assessment No. 117 (Prepared by University of Ottawa Evidence-based Practice Center under Contract No. 290-02-0021.) AHRQ Publication No. 05-E008-2. Rockville, MD: Agency for Healthcare Research and Quality. July 2005.
This report is based on research conducted by the University of Ottawa Evidence-based Practice Center (EPC), under contract to the Agency for Healthcare Research and Quality (AHRQ), Rockville, MD (Contract No. 290-02-0021). The findings and conclusions in this document are those of the authors, who are responsible for its contents; the findings and conclusions do not necessarily represent the views of AHRQ. Therefore, no statement in this report should be construed as an official position of AHRQ or of the U.S. Department of Health and Human Services.
The information in this report is intended to help health care decisionmakers, patients and clinicians, health system leaders, and policymakers make well-informed decisions and thereby improve the quality of health care services. This report is not intended to be a substitute for the application of clinical judgment. Anyone who makes decisions concerning the provision of clinical care should consider this report as they would any medical reference and in conjunction with all other pertinent information, i.e., in the context of available resources and circumstances presented by individual patients.
This report may be used, in whole or in part, as the basis for development of clinical practice guidelines and other quality enhancement tools, or as a basis for reimbursement and coverage policies. Neither AHRQ’s nor the U.S. Department of Health and Human Services' endorsement of such derivative products may be stated or implied.
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540 Gaither Road, Rockville, MD 20850. www
.ahrq.gov
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