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Prevalence of visual impairment in older people living with dementia and its impact: a scoping review
BMC Geriatrics volume 23, Article number: 63 (2023)
Abstract
Background and objectives
Visual impairment (VI) and dementia both increase with age, and it is likely that many older people are living with both conditions. This scoping review aims to investigate the prevalence and types of VI among older people living with dementia, and the impact of VI on older people living with dementia and their caregivers.
Methods
This scoping review used Arksey and O’Malley’s methodological framework. Studies in any setting involving people living with dementia and some assessment of either VI, eye diseases causing VI or the impact of VI were included.
Results
Thirty-six studies were included. Thirty-one studies reported the prevalence of VI in older people living with dementia, while ten studies reported on impacts of VI on people living with dementia. Only one study reported on impacts on caregivers. The prevalence of VI or specific eye diseases among older people living with dementia ranged from 0.2 to 74%. The impacts of VI on older people living with dementia included increased use of hospital services, increased disability and dependency, reduced social engagement, negative emotions, increased abnormal behaviours, loss of hobbies, difficulty in using visual aids or memory aids, and greater Neuropsychiatric Inventory symptoms. And the impacts on caregivers included increased conflict and physical exhaustion.
Conclusion
VI is common in older people living with dementia and is associated with negative impacts on those with dementia and their caregivers. However, heterogeneity between studies in terms of setting and method for assessing and defining VI make it difficult to compare findings among studies. Further research is needed, particularly assessing the impact on caregivers.
Introduction
Globally there were an estimated 43.8 million older people living with dementia in 2016 [1] and 173 million persons with severe or moderate visual impairment (VI) in 2010 [2]. Age is a risk factor for both conditions, meaning that the prevalence of both conditions increases with more advanced age. This also means that many older people are likely to be living with both conditions, with a likely increased impact on independence and quality of life.
As well as increasing the risk of harmful events such as falls, VI could increase the incidence of disorientation, confusion, inability to perform tasks of daily living, poor mental health and social isolation [3, 4].The presence of dementia in those with VI may hinder both the identification and management of vision impairment, leading to the exacerbation of both conditions [5]. It may also negatively impact on the self- management of chronic disease, leading to a higher utilization of healthcare services [6,7,8]. There is also an increased risk of family and carers experiencing feelings of exhaustion and depression [9]. Despite the expected increase in frequency of concurrent dementia and VI and the likely impact of concurrent VI on those living with dementia and their carers, there has been limited research describing the prevalence of VI in those living with dementia and its impact on quality of life and function in those living with dementia and their caregivers.
A previous scoping review by Bunn et al. explored the extent, range and nature of research in relation to dementia and comorbidity, with a specific focus on the comorbidities of diabetes, stroke and VI [10]. However, the literature search for this review was conducted in 2013 and only five studies that assessed the prevalence of VI were located, with four of the studies focusing on particular causes of VI such as glaucoma. In addition, there was minimal discussion of the impact of VI on those living with dementia apart from the impact on quality of care received. Finally, the impact of concurrent VI and dementia on caregivers was not assessed as part of the review. Our aim was to conduct a scoping review of the literature to identify and describe research about the prevalence and types of VI in older people living with dementia, and the impact of VI on older people living with dementia and their caregivers.
We aimed to answer three research questions: 1) What is the prevalence of VI in those living with dementia; 2) What is the impact of comorbid VI in those living with dementia; and 3) What is the impact of comorbid VI and dementia on caregivers of those living with dementia.
Methods
This scoping review was conducted based on Arksey and O’Malley’s methodological framework [11]. A protocol for the study was developed and a comprehensive search conducted in electronic databases.
Inclusion and exclusion criteria
We included studies involving people with any type of dementia in any setting with some measure of VI or eye diseases. In addition to studies on those living with dementia, studies of caregivers of people living with dementia and VI that measured the impact of combined dementia and VI on caregivers were included. We accepted any definition of VI including formally assessed visual acuity and self-reported VI. We also included studies that assessed the presence of common eye diseases in older people living with dementia such as age-related macular degeneration, glaucoma, cataract and diabetic retinopathy. Studies that examined visual symptoms or disorders of visual perception that were considered part of the dementia process, as opposed to a separate comorbidity, were excluded. We included all study types including cross-sectional, case-control, cohort, randomised controlled trials and qualitative studies in line with the broad scope of a scoping review.
Search strategy
A comprehensive literature search strategy (see Additional file 1) was developed in partnership with a medical librarian. We searched for published and unpublished literature with no date or language restrictions. Literature in languages other than English were translated using google translate or with the assistance of native speakers (see acknowledgement). Searches were conducted in Ovid MEDLINE, Embase, PsycINFO, CINAHL, Scopus, Web of Science, Google Scholar and Open Grey. The search was conducted on 13th April, 2020.
Selecting studies and charting the data
Two authors (WZ, FFS) screened titles and abstracts independently to select studies for inclusion. The full text of articles selected by either author in the initial screening stage were reviewed to select the final list of articles. Disagreements were resolved by discussion between WZ and FFS. Data were extracted independently by two authors (WZ, FFS) and checked for errors by comparing extracted data between both authors. Data extraction templates included information on authors, year of publication, country, study design, research question, inclusion/ exclusion criteria, representativeness, sample size, type of dementia, type of VI, how dementia/ VI were assessed, type of impact, how the impact was measured, size of effect and prevalence. Extracted data was reported narratively and summarized in tables. When a single study was published as several papers, these papers were grouped together and the one with the more complete data was considered the primary source. The quality of included studies was not formally assessed as this is a scoping review. However, data on study type, sample representativeness, sample size and the methods of diagnosing dementia and VI or other eye diseases was collected. We assessed the representativeness of study samples based on sampling methods and participation rates. Sampling methods considered representative included recruiting over a number of different sites to capture diverse populations in the community, or using insurance databases that have wide population coverage.
Results
A total of 5094 studies were identified after removal of duplicates (Fig. 1). After exclusion of non-relevant results by title and abstract screening, 165 articles were screened by full text and 37 studies (36 articles) included. Reasons for study exclusion included incorrect study population and no outcome data (no data on prevalence or impact of VI).
Overview of study characteristics
Of the 37 studies included, 34 studies were quantitative studies, three studies were qualitative studies, and one study provided both quantitative and qualitative data. Thirty-one provided data on prevalence and ten provided data on the impact of VI on older people living with dementia (Table 1). Only one qualitative study and one quantitative study provided data on the impact of comorbid VI on caregivers. Most studies were from the United States of America (USA) (nine studies) [13, 19, 23, 25, 28, 35, 38, 41, 43] and the United Kingdom (UK) (ten studies) [12, 16, 17, 22, 26, 27, 37, 44, 47]. Three studies were from China [21, 31, 33] and one global study [40] reported data from low- and middle-income countries (Table 1). The majority of studies recruited samples from the community (59%). Eight studies (22%) recruited participants from nursing homes and seven (19%) were conducted in hospitals or other health-care settings.
Among the prevalence studies, 18 (58%) studies were cross-sectional and 12 (39%) were case-control studies. Sixteen studies reported the prevalence of general VI. General VI was measured in different ways across studies including self-report [13, 23, 28, 36, 40], medical records [18, 19, 21, 22, 25,26,27, 30,31,32, 39, 41]or ophthalmologist assessment [14, 15, 17, 20, 24, 29, 33,34,35, 42, 44,45,46]. Fourteen studies [14, 15, 17,18,19, 21, 26, 31, 32, 34, 39, 41, 42, 46] reported the prevalence of glaucoma in various settings. Seven studies [17, 18, 24, 34, 41, 44, 46] reported the prevalence of aged-related macular degeneration (AMD). There was substantial variation among the seven studies in how the presence of AMD was determined. Three studies [17, 18, 34] measured the presence of AMD by optometric eye examination (prevalence 5 to 23%), three [24, 44, 46] studies through review of retinal photography by an experienced ophthalmologist (prevalence 17 to 41%), and one [41] study by autopsy and pathological diagnosis (prevalence of 53%). Only six studies [12, 17, 19, 27, 32, 46] reported the prevalence of cataract in which two studies were cross-sectional studies and reported a prevalence of cataract of 59% [17] and 21% [32].
Among the studies on the impact of VI, five (50%) studies were cross-sectional, two were cohort studies (20%) and three (30%) were qualitative studies. Lawrence et al. [47] published three papers (in 2009, 2010 and 2011) which presented results from one individual study. Bowen et al. [17] carried out two separate studies on different samples. One was a cross-sectional quantitative study on a large sample while the other one was a qualitative study on a small number of participants. Two studies were on the impact of VI on caregivers, in which one was a cross-sectional quantitative study [13] and the other one was a qualitative study [3]. Five of the quantitative studies were cross-sectional [17, 28, 29, 38, 40] and only two were longitudinal [16, 23]. Two of the qualitative studies [37, 47] only included participants with both dementia and VI, with no comparison with those living with dementia alone.
Prevalence
Thirty-one studies provided data on the prevalence of VI or specific eye diseases in older people living with dementia in various settings (Table 2). Sixteen studies reported the prevalence of general VI with prevalence rates ranging from 0.4 to 52% [12, 13, 17, 19, 20, 22, 23, 25, 28,29,30, 33, 35, 36, 40, 45].
Fourteen studies [14, 15, 17,18,19, 21, 26, 31, 32, 34, 39, 41, 42, 46] reported the prevalence of glaucoma in various settings with prevalence ranging from 0.2 to 26%. Prevalence was substantially higher in studies in nursing homes [14, 15, 18, 42]. Seven studies [17, 18, 24, 34, 41, 44, 46] reported the prevalence of aged-related macular degeneration (AMD) in various settings, which ranged from 5 to 53%. Only six studies [12, 17, 19, 27, 32, 46] reported the prevalence of cataract with prevalence ranging from 0.2 to 74%. As well as variation in settings, there was variation in how the presence of cataract was assessed including an eye exam by an optometrist (prevalence of 59%) [17], review of medical records (prevalence of 23 and 21%) [27], review of retinal photographs by an ophthalmologist (prevalence of 74%) [46], and review of death certificates (prevalence of 0.2%) [18]. As death certificates only list major diseases, some minor diseases such as cataract may be missed leading to the low prevalence of VI when using this method to measure the presence of cataract. The prevalence of diabetic retinopathy was reported in only two studies [17, 46], with a prevalence of 19% in a hospital-based study in Singapore [46] and 2% in a community-based study in the UK [17]. In addition to prevalence, Bowen et al. also commented on the proportion of VI or eye diseases that were potentially reversible [17]. They found that much VI was due to refractive error that could be remediated by corrective lenses and eye diseases such as cataract that are amenable to surgical correction [17].
Impact of VI in older people living with dementia
Ten studies (seven quantitative and three qualitative) provided data on the impact of VI in older people living with dementia (Table 3 and Table 4). There were a range of impacts examined in the studies including use of hospital services, level of disability and dependency, social engagement, negative emotions, abnormal behaviors, loss of hobbies, difficulty in using visual or memory aids, and Neuropsychiatric Inventory (NPI) symptoms.
Two cohort studies [16, 23] investigated increased use of hospital services by those with comorbid dementia and VI. Deardorff et al. [23] found that people with concurrent VI and dementia had a higher risk of inpatient admission when compared to older people living with dementia without VI or hearing impairment (HI) (Odds Ratio (OR) =1.82, 95% Confidence Interval (CI) = 1.17–2.82). However, there was no significant difference in odds of inpatient admission in older people living with dementia who had HI only or both VI and HI compared to those with no VI or HI. Hence, in this particular study the effect of VI was differentiated from the effect of HI and it appears that VI had an impact on hospital admission, whereas HI did not. There was also an increased likelihood of hospice use in those with comorbid visual and hearing impairment and dementia compared to those living with dementia alone (OR = activity limitation, 95%CI 1.05–4.21). But, there was no significant difference in older people living with dementia who had HI only or VI only compared to those with no VI or HI. Therefore, for this outcome it is difficult to differentiate between the effect of VI and HI but the effects do appear to be additive.
In regards to health costs, no differences were observed in total annual health costs and annual medical fee-for-service costs between those living with dementia with and without sensory impairment. Bennett et al. [16] found increased inpatient visits in those living with dementia and VI compared to those with VI alone (Cognitive Function and Ageing Study (CFAS))(CFAS I: OR = 3.5, 95%CI = 1.1–11.5; CFAS II: OR = 1.7, 95%CI = 0.9–3.2).
Decreased Activities of Daily Living (ADLs) was reported in three cross-sectional studies [17, 38, 47]. In a large study of community-dwelling people living with dementia in the UK, comorbid VI (defined as Visual acuity (VA) < 6/12) compared to dementia without VI was significantly associated with less independence in ADLs (P < 0.05) [17]. Patel et al. [38] found that people with possible dementia and VI had more activity limitation compared to those with no dementia and no sensory impairments (OR = 1.97, 95%CI 1.72–2.21) and that this was greater than the activity limitation observed in those with possible dementia alone compared to those with no dementia and no sensory impairments (OR = 1.24, 95%CI 1.14–1.33). Conversely, there did not seem to be a greater association of VI and probable dementia on activity limitations compared to probable dementia alone, which suggests that VI may not lead to any additional limitations on the activities of older people living with dementia.
A further three studies reported the impact of comorbid VI on increased dependence in older people living with dementia [16, 37, 47]. In a longitudinal study, Bennet et al. [16] found that use of care workers was about six times greater in older people living with dementia and VI in two samples (CFA I: OR = 5.8, 95%CI = 1.8–19.2; CFA II: OR = 6.4, 95% CI = 2.6–15.5) compared to those with VI without dementia. In addition, the use of home help in the previous 4 weeks before the interview was three to four times greater (CFA I: OR = 4.4, 95%CI = 1.3–15.0; CFA II: OR = 3.4, 95% CI = 1.3–8.5). A global study on the impact of VI in those living with dementia found a cross-sectional association with disability in some settings [40]. Participants living with dementia and VI in Latin America (Mean difference = 6.5, 95% CI = 3.3–9.6) and India (Mean difference = 12.3, 95% CI = 5.4–19.3) had a significantly higher score on the World Health Organization Disability Assessment Schedule than those living with dementia without VI.
Lawrence et al. [47] carried out a qualitative study in people with both dementia and VI and found that they experienced disorientation due to an inability to see the clock or read the date, increasing their dependency on others. Further, they were unable to compensate for poor memory using visual cues or compensate for poor vision with cognitive strategies, resulting in a greater impact of both conditions. Caregivers’ increased concerns over their safety meant that there were often increased restrictions placed on their activities. Another community-based qualitative study in the UK of people with VI and dementia also found greater dependence [37]. However, similar to the previous study, there was no comparison with people living with dementia alone.
The qualitative study by Lawrence et al. [47] also found that people with dementia and VI felt lonely and isolated. They suffered from difficulties in initiating social contact and identifying when conversation was directed at them. This added to the burden of engaging in group conversations, leading to decreased social engagement. A South Korean cross-sectional study [28] also found a statistically significant association between VI and reduced social engagement (P = 0.021) in a group of older people living with dementia.
A negative emotional impact was reported in two qualitative studies [37, 47]. Nyman et al. [37] found that older people living with dementia and VI felt bored and lacked daily stimulation as reported by themselves and their caregivers. However, the study did not include any older people living with dementia alone to enable comparison of the added impact of VI. Lawrence et al. [47] found that older people living with dementia and VI who felt distressed sometimes manifested this distress as agitated and aggressive behavior. In a cross-sectional analysis, Kiely et al. [29] also found that VI was associated with greater NPI symptoms in those living with dementia (Incidence rate ratio (IRR) = 7.08, 95% CI = 1.41–35.43) compared to those without VI or dementia. Those living with dementia alone did not demonstrate significantly greater NPI symptoms (IRR = 1.63, 95%CI = 0.73–3.63).
The loss of hobbies is another important impact which was reported in two qualitative studies [17, 47] where respondents reflected on experiences before and after developing VI. For example, Bowen et al. [17] reported a caregiver who stated that his wife living with dementia had to give up her hobby of reading due to VI. Participants in the study by Lawrence et al. [47] also reported that joint VI and memory loss restricted interests and hobbies and meant that those living with dementia and VI needed to be stimulated by others.
Impact of VI on caregivers of older people living with dementia
There were only two studies (one qualitative and one quantitative) that specifically investigated the added impact of VI to dementia on caregivers, both in a community setting [43, 47] (Tables 3 and 4). A UK qualitative study reported negative impacts on caregivers of those living with dementia and VI including negative emotions and loss of hobbies [17]. However, there was no comparison group of caregivers of those living with dementia alone. Caregivers also reported conflict when taking care of older people living with both dementia and VI due to concerns about safety resulting in greater restrictions of valued activities and roles of those living with dementia. Caregivers also reported physical exhaustion due to the high dependency level of those with dementia and preventing them from leaving the older person with dementia alone. The second study was a cross-sectional quantitative study comparing experiences of caregivers of older people living with dementia and VI, with dementia only, VI only or no dementia or VI. Results demonstrated that caregivers of older people living with concurrent dementia and VI had less time to participate in activities such as: visiting friends and family, going out for enjoyment, attending religious services, and participating in club meetings or group activities. Moreover, caregivers of people living with dementia and VI spent 1.7 times more hours on caregiving (95% CI = 1.4–2.2) than caregivers of those without either dementia or VI. In contrast caregivers of those living with dementia only spent 1.3 times more hours of caregiving (95% CI = 1.1–1.6) compared to caregivers of those with no dementia or VI.
Discussion
In this scoping review we found that VI is common in older people living with dementia with the prevalence varying based on the setting and method of measurement of VI. Glaucoma, AMD, cataract and diabetic retinopathy were also common. Concurrent VI resulted in multiple different impacts on older people living with dementia and their caregivers. However, research on the impacts of concurrent VI on caregivers was quite limited.
Despite being able to locate a few studies reporting the prevalence of VI in older people living with dementia, a clear understanding of the prevalence of VI and common eye diseases in this population based on current research is not possible given the heterogeneity between studies in terms of setting, age of participants, and how VI and eye diseases were defined and measured. How VI is measured is a particularly important consideration, given that VI in older people living with dementia is likely to be under-diagnosed [17] with measurement based on of self-report, medical records, claims data and death certificates likely to underestimate prevalence. In addition, the use of definitions that include the use of glasses to define VI do not adequately capture the likely differential impact of having VI adequately corrected or not. The study by Bowen et al. [17] was the only study that carried out formal visual acuity assessments in a large cohort recruited from 20 National Health Service sites in six English regions. Participants from both a community and nursing home setting were included and the prevalence estimates of 32.5% (with spectacles and VA < 6/12) and 16.3% (with spectacles and VA < 6/18) are likely to be the most accurate estimates of prevalence of VI in older people living with dementia.
Many of the studies that provided data on the prevalence of different eye conditions were case-control studies of very small sample size that were primarily conducted to determine causal relationships between particular eye diseases and dementia rather than to estimate prevalence [14, 15, 24, 27]. In many of these studies it was unclear how representative the cases of dementia were and, as a result, the reported data are unlikely to provide an accurate estimate of prevalence. There was also surprisingly little data on the prevalence of cataract in those living with dementia and the studies that were conducted had different study designs, were in different settings and used different methods for assessing the presence of cataract resulting in a wide range of prevalence estimates (0.2 to 74%). Similar to VI, the best estimate of cataract prevalence is that of 59% (95%CI 55.2 to 62.7%) reported by Bowen et al. [17] which measured cataract with an eye exam by an optometrist in a representative sample of people living with dementia living in the community or nursing homes. Surprisingly only two studies reported on the prevalence of diabetic retinopathy among older people living with dementia [17, 46].
Our results demonstrate that despite the seemingly high prevalence of VI and eye diseases in older people living with dementia, there is a significant unmet need with limited research done to accurately estimate this prevalence. In particular, there is a need for research that includes assessments by optometrists and/or ophthalmologists to more accurately determine VI and eye diseases. Given that the study by Bowen et al. [17] found that much VI was due to refractive error that could be remediated by corrective lenses, or eye diseases such as cataract that are amenable to surgical correction, identifying the presence of these common and treatable eye conditions in older people living with dementia is of clear importance to public health. Preventable vision loss due to cataract (reversible with surgery) and refractive error (reversible with spectacle correction) continue to cause most cases of blindness and moderate or severe vision impairment in adults aged 50 years and older [48].
We found evidence of a range of negative impacts of VI in people living with dementia and two studies suggesting negative impacts on their caregivers. Similar to prevalence, we observed large heterogeneity in how VI and eye diseases were measured and defined and we would recommend that future studies of the impact of VI on those living with dementia should have a clear definition of VI, confirmed by a comprehensive visual assessment rather than being self-reported. There is also a need for more longitudinal studies as most studies examining the impact of comorbid VI on those living with dementia were cross-sectional, which makes it harder to establish a causal relationship. Moreover, several studies examining the impact of comorbid VI and dementia either had inappropriate or no comparators to adequately examine the additional impact of having VI in people living with dementia. For example, a longitudinal study found that use of care workers was six times greater in older people living with dementia and VI in two samples [16]. However, this was compared to those with VI without dementia rather than those living with dementia without VI. A few qualitative studies reported a range of negative impacts, including on ADL function, social isolation and psychological health. These qualitative studies only included older people living with concurrent dementia and VI and no comparison group. Hence, it is difficult to be sure what negative impacts are due to the added presence of VI and what impacts are the result of dementia itself.
There are also many potential impacts that have not been assessed, such as the impact of VI in those living with dementia on the risk of falls. Although both VI and dementia are known falls risks factors [49, 50], it is not known whether the combined presence of these two conditions greatly multiplies this risk. Our scoping review also found only a limited number of studies looking at the impact of concurrent VI and dementia on caregivers, with only one qualitative study and one quantitative study addressing this topic [43, 47]. Many studies reporting comments from caregivers were about the impact of VI on those living with dementia, rather than the impact of VI on themselves as part of their caring role. Therefore, an important area of further study would be to investigate the impact of VI on caregivers of those living with dementia, including consideration of health outcomes of caregivers. Impact on health service use and health expenditure is another key area that requires more research. Again, we found only one study that examined use of health and support services [17], but the lack of an appropriate comparator group prevented assessment of the added impact of VI on health service use in those living with dementia. Given population ageing, the number of people with concurrent dementia and VI will sharply grow over coming years, and assessment of the impact of these comorbid conditions on health expenditure and research into interventions aimed at reducing this expenditure by better management of VI in those living with dementia is crucial.
To our knowledge, this is the first scoping review to examine specifically the prevalence of VI in people living with dementia and the impact of VI on people living with dementia and their caregivers. We have identified important gaps in the evidence-base that should be addressed by future research. A limitation of our approach is that as we conducted a scoping review, we did not conduct a formal assessment of the quality of included studies. However, we did consider the representativeness and setting of studies, study design and definition of VI due to the enormous variation in these aspects between studies.
Conclusions
In conclusion, VI is common in older people living with dementia and is associated with negative impacts on those living with dementia and their caregivers. We conducted a systematic search across a large number of electronic databases identifying important gaps in the literature., The heterogeneity between studies in terms of setting and method for assessing VI make it difficult to compare findings between studies. Research is limited, particularly in terms of impacts on caregivers and longitudinal research. This review emphasizes the importance of managing vision problems in older people living with dementia and provides directions for future targeted research on this relatively neglected topic.
Availability of data and materials
All data generated or analyzed during this study are included in this published article (and its supplementary information files).
Abbreviations
- ADLs:
-
Activities of Daily Living
- AMD:
-
Aged-related macular degeneration
- CFAS:
-
Cognitive Function and Ageing Study
- CI:
-
Confidence interval
- IRR:
-
Incidence rate ratio
- NPI:
-
Neuropsychiatric Inventory
- OR:
-
Odds Ratio
- UK:
-
The United Kingdom
- US:
-
The United States
- VA:
-
Visual acuity
- VI:
-
Visual impairment
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Acknowledgements
The authors are indebted to the support from Dr. Naomi Noguchi who helped translate one Japanese paper.
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WZ, TR, CP and FS were responsible for the idea for the study and development of the research questions. FS and WZ developed the research proposal, screened the results and extracted the data. WZ drafted the manuscript. TR, CP and FS contributed to critical revision of the manuscript. WZ, TR, CP and FS all approved the final version of the completed manuscript.
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Zhang, W., Roberts, T.V., Poulos, C.J. et al. Prevalence of visual impairment in older people living with dementia and its impact: a scoping review. BMC Geriatr 23, 63 (2023). https://doi.org/10.1186/s12877-022-03581-8
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DOI: https://doi.org/10.1186/s12877-022-03581-8