Definition of childhood visual impairment: A systematic overview of reviews and authoritative sources across clinical, research, and policy contexts

AIMS: To identify, synthesize, and compare current terminologies and definitions of cerebral visual impairment (CVI) in children across clinical, research, educational, and policy settings. METHOD: We conducted a systematic overview of systematic reviews and authoritative documents registered in PROSPERO (CRD420251025233) and reported in accordance with the PRISMA 2020 guidelines. We searched PubMed, Embase, CINAHL, Scopus, ProQuest Health and Medical, Web of Science, and the Cochrane Library for records published from 1st January 2015 to 10th April 2025, without language restrictions. Records were screened independently by pairs of reviewers. We performed manual searches of websites from governmental organizations, national health authorities, CVI societies, and international professional bodies. RESULTS: Forty-eight systematic reviews and 26 authoritative documents were included. CVI was most commonly defined using World Health Organization-based or International Classification of Diseases-based distance visual acuity thresholds, typically defining visual impairment as a visual acuity worse than 6/12 in the better-seeing eye and blindness as visual acuity worse than 3/60. Visual field loss and near visual impairment were incorporated less consistently. Systematic reviews tended to prioritize measurable criteria, typically visual acuity in the better-seeing eye, whereas authoritative documents more frequently linked visual impairment to functional consequences for learning and daily activities. CVI was described in a subset of sources as brain-based visual dysfunction not fully explained by ocular pathology, but definitions and severity criteria varied widely. Few documents included structured functional vision assessment. INTERPRETATION: CVI definitions remain heterogeneous and incompletely reflect real-world visual functioning, especially for CVI and functional vision. Consensus is needed on child-centred, multidimensional definitions integrating ocular and brain-based causes, multiple visual functions, and functional impact across sectors. A working definition of CVI is needed and has been proposed in this review.