Performance Comparison of Smartphone-Based Portable Slit Lamp Microscopes: A Narrative Review of Medical Devices Applicable to Telemedicine in Ophthalmology

Smartphone-based portable slit lamp microscopes are increasingly used as low-cost tools for anterior segment imaging in teleophthalmology, yet the literature combines heterogeneous study designs, comparator standards, and deployment contexts. Because the evidence base spans engineering reports, basic science, clinical validation studies, implementation research, and case-based telemedicine, we structured a narrative review rather than a pooled meta-analysis. We searched PubMed/MEDLINE, Embase, Scopus, Web of Science, Google Scholar, Cochrane Library, ScienceDirect, and DOAJ for literature available on or before 28 February 2026, supplemented by manual reference list screening and targeted retrieval of relevant technical standards. Peer-reviewed English original studies formed the core evidence base; contextual non-English and gray literature sources were retained only when explicitly labeled as non-core. To improve interpretability, the results were grouped by synthesis domain, clinical task, comparator standard, telemedicine scenario, and artificial intelligence (AI) dataset/validation characteristics. The highest-confidence evidence concerned nuclear cataract grading, tear film breakup time and corneal staining assessment, anterior chamber depth screening, tear meniscus height measurement, allergic conjunctival grading, and selected corneal disorders. Agreement with conventional slit lamp examination or anterior segment optical coherence tomography was generally moderate to high within task-specific comparisons, and telemedicine deployment was feasible for screening, follow-up, remote consultation, emergency triage, house visits, and outreach. However, illumination reporting remains inconsistent, explicit ISO-aligned dosimetry is sparse, and most AI studies remain retrospective, single-center, and device family-specific. Current evidence, therefore, supports smartphone-based portable slit lamp microscopes primarily as adjunctive teleophthalmology tools rather than replacements for comprehensive in-clinic microscopy. The synthesis clarifies where conclusions are supported by comparative validation data, where they remain exploratory, and which methodological gaps should be prioritized in future multicenter studies.