Re: Shang Et Al.: the Association Between Vision Impairment and Incidence of Dementia and Cognitive Impairment: a Systematic Review and Meta-Analysis (ophthalmology. 2021;128:1135–1149)

We read with interest the systematic review and meta-analysis by Shang et al,1Shang X. Zhu Z. Wang W. et al.The association between vision impairment and incidence of dementia and cognitive impairment: a systematic review and meta-analysis.Ophthalmology. 2021; 128: 1135-1149Abstract Full Text Full Text PDF Scopus (9) Google Scholar who investigated the association between vision impairment (VI) and incident dementia/cognitive impairment (CI). The authors found that the presence of VI was significantly associated with 1.47 and 1.35 times the risk of incident dementia and CI, respectively. We commend the authors on performing detailed subanalyses of their data, such as sensitivity analyses of the methods to assess vision (e.g., objective charts versus self-reported scales), length of follow-up and study quality based on the Newcastle-Ottawa Scale, and calculation of the population attributable risk of dementia associated with VI. We nevertheless seek a few clarifications on the definitions of the study’s outcome and exposure variables. First, the authors did not define VI in this article. The visual function system consists of many components, including visual acuity, visual field, contrast sensitivity, color vision, and stereopsis.2Committee on Disability Determination for Individuals with Visual Impairments. Tests of visual functions.in: Lennie P. Hemel S.B.V. Visual Impairments: Determining Eligibility for Social Security Benefits. National Academies Press, Washington, DC2002: 51-125Google Scholar This information is important, because different pathologies of dementia/CI may present with distinct ocular symptoms,3Vu T.A. Fenwick E.K. Gan A.T.L. et al.The bidirectional relationship between vision and cognition: a systematic review and meta-analysis.Ophthalmology. 2021; 128: 981-992Abstract Full Text Full Text PDF Scopus (10) Google Scholar and it is possible that the associations between different aspects of the visual function system and incident dementia/CI may differ and therefore should be meta-analyzed separately. Indeed, in a systematic review and meta-analysis conducted by Vu et al3Vu T.A. Fenwick E.K. Gan A.T.L. et al.The bidirectional relationship between vision and cognition: a systematic review and meta-analysis.Ophthalmology. 2021; 128: 981-992Abstract Full Text Full Text PDF Scopus (10) Google Scholar on a similar topic published in Ophthalmology, the authors explicitly defined VI based on visual acuity and visual field in agreement with the International Classification of Diseases, 11th Revision, criteria of VI and blindness. Second, although the primary study outcome reported by Shang et al—dementia —was based on the internationally accepted criteria from the Diagnostic and Statistical Manual of Mental Disorders, the definition of the study’s secondary outcome—CI—is debatable. According to the National Institute of Aging–Alzheimer’s Association Research Framework, CI is an umbrella term that encompasses preclinical, mild CI, and dementia stages.4Jack Jr., C.R. Bennett D.A. Blennow K. et al.NIA-AA Research Framework: toward a biological definition of Alzheimer's disease.Alzheimers Dement. 2018; 14: 535-562Abstract Full Text Full Text PDF PubMed Scopus (2623) Google Scholar Although brief cognitive screening questionnaires such as the Mini-Mental Status Examination and the Telephone Interview for Cognitive Status can be used to screen for CI, CI diagnosis, and further classification of CI into mild CI or dementia stages require the gold standard clinical evaluation performed by physicians in agreement with international consensus criteria.5National Institute for Health and Care ExcellenceNational Institute for Health and Care Excellence: Clinical Guidelines.Dementia: Assessment, management and support for people living with dementia and their carers. 97. National Institute for Health and Care Excellence (UK), London2018Google Scholar Therefore, cognitive screening questionnaires are less accurate as compared with clinical evaluation and tend to overestimate the incidence of CI in visually impaired individuals. Consequently, it may not be appropriate to combine these outcomes into a single meta-analysis to examine the association between VI and incident CI. Overall, the findings by Shang et al1Shang X. Zhu Z. Wang W. et al.The association between vision impairment and incidence of dementia and cognitive impairment: a systematic review and meta-analysis.Ophthalmology. 2021; 128: 1135-1149Abstract Full Text Full Text PDF Scopus (9) Google Scholar are very encouraging; VI may be a modifiable risk factor of both dementia and CI in older adults. This is clinically important and supports the notion that early vision screening and interventions may be an effective risk-reduction strategy for dementia and CI . Nevertheless, these findings will need to be interpreted with some caution due to unclear definitions of VI and CI used in the study. We seek further information from the authors on how VI and CI were defined along with any potential implications of not performing separate meta-analyses to account for different visual function and CI outcomes. The Association between Vision Impairment and Incidence of Dementia and Cognitive Impairment: A Systematic Review and Meta-analysisOphthalmologyVol. 128Issue 8PreviewThe magnitude and direction of the association between vision impairment and incident dementia and cognitive impairment in prospective cohort studies was estimated by systematic review and meta-analysis. The global burden of dementia associated with vision impairment then was estimated. Full-Text PDF ReplyOphthalmologyVol. 128Issue 8PreviewWe appreciate the comments by Vu et al on our systematic review and meta-analysis regarding vision impairment and incidence of dementia and cognitive impairment. Full-Text PDF