Conducting a Literature Review

Think of this as a scholarly essay. The author gathers existing research on a topic and weaves it into a cohesive story. It’s great for providing context or a broad overview, but it can be prone to "cherry-picking" since there isn't a strict protocol for which studies are included.

• Best for: Educational overviews and general updates.
• Key Feature: Qualitative and broad in scope.
• Example: Grewal BK, Britten-Jones AC, Metha AB, Bedggood PA, Ayton LN. Integrating adaptive optics imaging into inherited retinal disease treatment trials: a narrative review. Expert Review of Ophthalmology. 2026;21(3):203-218. doi:10.1080/17469899.2026.2645147
• Estimated time for completion: 1-4 weeks

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Think of this as a systematic review lite. It follows the same rigorous steps as a systematic review but simplifies certain stages (like limiting the search to the last five years or using only one reviewer) to produce information quickly.

• Best for: Policymakers or clinicians who need an answer now (e.g., during a public health crisis).
• Key Feature: Speed over absolute exhaustiveness.
• Example: Oxford Centre for Evidence-Based Medicine. Rapid Review: Diabetic Retinopathy Screening During the COVID-19 Pandemic. COVID-19 Evidence Service; 2020. Accessed June 26, 2026. https://www.cebm.net/covid-19/diabetic-retinopathy-screening-during-the-covid-19-pandemic/
• Estimated time for completion: 3-8 weeks

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If you aren’t sure how much research actually exists on a topic, you do a scoping review. It’s used to "map" the available evidence, identify key concepts, and spot gaps in the literature. It’s less about "quality appraisal" and more about extending the boundaries of a field.

• Best for: New or emerging fields where a systematic review might be premature.
• Key Feature: Focuses on the "breadth" rather than the "depth."
• Example: Chen AM, Salzano AD, Burgher AP, et al. Scoping review: Intervention for ocular motor disorders in children and adults with mild traumatic brain injury. Optometry and vision science : official publication of the American Academy of Optometry. 2025;102(4):204-214. doi:10.1097/OPX.0000000000002237
• Estimated time for completion: 3-6 months

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This is the gold standard for evidence-based research. Unlike the narrative review, a systematic review follows a strict, pre-defined protocol to find, appraise, and synthesize every single relevant study on a specific question. It’s designed to be transparent and reproducible to minimize bias. Simply put: they are a massive undertaking.

• Best for: Answering specific clinical or technical questions.
• Key Feature: High rigor and exhaustive search strategy.
• Example: Malkin A, Deemer A, Contreras M, et al. Self-management interventions for quality of life in adults with visual impairment. The Cochrane database of systematic reviews. 2025;2. doi:10.1002/14651858.CD015790.pub2
• Estimated time for completion: 9-18 months

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Often performed alongside a systematic review, a meta-analysis uses statistical methods to combine data from multiple independent studies. By "pooling" the results, it creates a much larger sample size, which provides a more definitive answer than any single study could.

• Best for: Determining the overall effect size of a treatment or phenomenon.
• Key Feature: Quantitative and data-driven.
• Example: Lange CA, Qureshi R, Pauleikhoff L. Interventions for central serous chorioretinopathy: a network meta-analysis. The Cochrane database of systematic reviews. 2025;6. doi:10.1002/14651858.CD011841.pub3
• Estimated time for completion: 12-18 months

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• When a topic has been researched so much that there are already multiple systematic reviews available, researchers conduct an umbrella review. It synthesizes the findings of other reviews into one high-level document.
• Best for: Compiling the highest level of evidence available in a field.
• Key Feature: The unit of analysis is the "review," not the "primary study."
• Example: Shen RY, Zhang Y, Chen LJ, et al. Ocular and Systemic Risk Factors and Biomarkers for Primary Glaucoma: An Umbrella Review of Systematic Reviews With Meta-Analyses. Investigative ophthalmology & visual science. 2025;66(12):35. doi:10.1167/iovs.66.12.35
• Estimated time for completion: 12+ months

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