The Relationship Between Sensory Loss and Health Literacy in Older Adults: A Systematic Review

Abstract

Objectives:

As sensory loss may impact the ability to receive and apply health information, a relationship between sensory loss and health literacy may exist. The purpose of this systematic review was to explore the relationship between hearing, vision and dual sensory loss and health literacy in older adults.

Methods:

Studies examining the relationship between sensory loss and health literacy in older adult populations using a validated health literacy instrument were included. The search was conducted in the CINAHL, PubMed, Scopus, AgeLine and REHABdata databases in May-June 2021.

Results:

Nine studies were included. Findings revealed a positive association between hearing and vision loss and low health literacy.

Discussion:

This review highlights a relationship between hearing and vision loss and low health literacy. The small number of studies and overall heterogeneity of study methods limits strength of this evidence. Individuals with sensory loss may benefit from additional clinician support in receiving and applying health information.

Introduction

Hearing, vision, and dual (combined hearing and vision) sensory loss are widely prevalent in older people. Hearing loss affects 68% of people over 70 years¹ and vision loss affects 24% of those 70–79 and 50% of those 80 years and over.² Dual sensory loss affects 11% of those over 80 years, and only 19% of those over 80 years do not have sensory loss.³ The incidence of sensory loss increases with age, leaving older people to bear the greatest burden of living with these far-reaching conditions.^1,3,4

As the population ages, the number of older adults with sensory loss is expected to grow. By 2050, it is estimated that there will be a 25% per decade increase in vision loss in people 40 and over.² By 2060, the number of people with hearing loss is projected to double.⁵ The current prevalence and projected growth of sensory loss necessitate a thorough understanding of hearing, vision and dual sensory loss’ impact on individual and population health outcomes for older adults. Hearing loss is associated with cognitive decline,⁶ increased risk of dementia,⁷ loneliness and social isolation,⁸ and mortality.⁹ Vision loss is associated with cognitive decline,¹⁰ dementia,¹¹ mortality,¹² depression,¹³ and falls.¹⁴ Dual sensory loss is associated with a greater risk of dementia,¹⁵ depression,^13,16 and poor quality of life¹⁷ than a single impairment alone. Hearing and vision loss are often undertreated^18,19 and continue to be associated with greater health care utilization and costs of care.^20–23 The reason for adverse health and utilization outcomes in this population is unclear. Still, effective communication between a clinician and patient is known to impact health outcomes and components of self-care management such as adherence to treatment.²⁴ However, hearing and vision loss creates communication challenges, and may impede an individual’s ability to see, hear, understand, and apply health information to support self-care. This is where sensory loss intricately intersects with health literacy.

Health literacy is defined as “people’s knowledge, motivation and competences to access, understand, appraise, and apply health information in order to make judgments and make decisions in everyday life concerning healthcare, disease prevention and health promotion to maintain or improve quality of life during the life course”.²⁵ Low health literacy results in poor outcomes such as higher mortality,^26,27 poorer ability in understanding health information,²⁸ greater use of health services and greater costs.^28,29 Due to challenges inherent in sensory loss, hearing and vision loss may impact the ability to adequately communicate with providers and understand health information, impeding the use of health information for self-care management. Identifying a relationship between sensory loss and health literacy may provide insight into the adverse health outcomes and greater healthcare utilization experienced by this population. Therefore, an investigation of the relationship between sensory loss and health literacy status is necessary. The purpose of this systematic review was to examine the evidence to answer the following question: “What is the relationship between hearing loss, vision loss, and dual sensory loss and health literacy status in older adults?”

Methods

This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement³⁰ and the National Institutes of Health (NIH) National Heart, Lung, and Blood Institute (NHLBI) Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies quality appraisal guidelines (2021). Study findings are presented in narrative format.

Eligibility Criteria

Studies were included if the sample had an older adult population (at least 65 years) or the mean or median age of general adult populations was at least 50 years. Quantitative studies investigating the relationship between hearing loss and health literacy, vision loss and health literacy, or dual sensory loss and health literacy were considered. Studies must have included an analytic comparison (to a group without sensory loss, across sensory loss severity groups, or by comparing sensory loss severity by health literacy status) to support examination of the relationship between sensory loss and health literacy. Solely descriptive studies were therefore excluded. No other limitation on study design was imposed. Only studies measuring health literacy with a validated instrument were included to examine health literacy as a concept most closely aligned with its definition. Original research was included, with reviews and case studies excluded. Only studies in English were included. Studies including deaf or blind populations were excluded.

Search Strategy

A health science librarian was consulted for assistance with the search strategy. In May and June of 2021, author LW searched the following databases: CINAHL, PubMed, Scopus, AgeLine, and REHABdata. LW conducted three searches per database to initially organize searches by impairment type. For instance, the first search included three primary keywords— “older adults,” “health literacy,” and “vision impairment” with related terms (e.g., vision loss). The keywords remained the same for each database search, but related terms were adapted for each database, and subsequent searches replaced “vision impairment” with “hearing impairment” and “dual sensory impairment.” The search was limited to articles published in the last 20 years. We also reviewed references of articles selected for full-text review to search for additional studies meeting criteria. An example of the complete search strategy for PubMed and CINAHL is available in Table 1.

Table 1:

Example of Search Strategy

Database	Topic	Search
PubMed	Health Literacy + Older Adults + Vision	(“Health Education”[Mesh] OR “Health Knowledge, Attitudes, Practice”[Mesh] OR “Health Education”[Mesh] OR “health literacy” OR “health literate”) AND (“Aged”[Mesh] OR “Health Services for the Aged”[Mesh] OR “elderly”[Title/Abstract] OR gerontology OR geriatr* OR “older adult*”[title/abstract]) AND (“lens diseases”[Mesh] OR “retinal diseases”[Mesh] OR “refractive errors”[Mesh] OR hemianopsia OR “vision, low” OR scotoma OR amblyopia OR “glaucoma” OR “macular degeneration” OR “cataract*” OR “vision impairment”[Title/Abstract] OR “vision loss”[title/abstract]) AND (1990:2021[pdat])
PubMed	Health Literacy + Older Adults + Hearing	(“Health Education”[MeSH Terms] OR “health knowledge, attitudes, practice”[MeSH Terms] OR “Health Education”[MeSH Terms] OR “health literacy”[All Fields] OR “health literate”[All Fields]) AND (“Age-Related Hearing Impairment 1”[Supplementary Concept] OR “hearing loss”[MeSH Terms] OR “hearing impair*”[Title/Abstract] OR “Persons With Hearing Impairments”[MeSH Terms] OR “hearing loss, bilateral”[MeSH Terms] OR “hearing loss, conductive”[MeSH Terms] OR “hearing loss, high frequency”[MeSH Terms] OR “hearing loss, mixed conductive sensorineural”[MeSH Terms] OR “mixed hearing loss”[All Fields] OR “hearing loss, sensorineural”[MeSH Terms] OR “hearing loss, unilateral”[MeSH Terms]) AND (“Aged”[MeSH Terms] OR “Health Services for the Aged”[MeSH Terms] OR “elderly”[Title/Abstract] OR (“geriatrics”[MeSH Terms] OR “geriatrics”[All Fields] OR “gerontology”[All Fields] OR “gerontologie”[All Fields] OR “gerontology s”[All Fields]) OR “geriatr*”[All Fields] OR “older adult*”[Title/Abstract]) AND 1990/01/01:2021/12/31[Date - Publication]
PubMed	Health Literacy + Older Adults+ Hearing AND Vision OR Dual Impairment	(((“Health Education”[MeSH Terms] OR “health knowledge, attitudes, practice”[MeSH Terms] OR “Health Education”[MeSH Terms] OR “health literacy”[All Fields] OR “health literate”[All Fields]) AND (“Age-Related Hearing Impairment 1”[Supplementary Concept] OR “hearing loss”[MeSH Terms] OR “hearing impair*”[Title/Abstract] OR “Persons With Hearing Impairments”[MeSH Terms] OR “hearing loss, bilateral”[MeSH Terms] OR “hearing loss, conductive”[MeSH Terms] OR “hearing loss, high frequency”[MeSH Terms] OR “hearing loss, mixed conductive sensorineural”[MeSH Terms] OR “mixed hearing loss”[All Fields] OR “hearing loss, sensorineural”[MeSH Terms] OR “hearing loss, unilateral”[MeSH Terms]) AND (“lens diseases”[MeSH Terms] OR “retinal diseases”[MeSH Terms] OR “refractive errors”[MeSH Terms] OR (“hemianopsia”[MeSH Terms] OR “hemianopsia”[All Fields] OR “hemianopsias”[All Fields]) OR “vision low”[All Fields] OR (“scotoma”[MeSH Terms] OR “scotoma”[All Fields] OR “scotomas”[All Fields]) OR (“amblyopia”[MeSH Terms] OR “amblyopia”[All Fields] OR “amblyopias”[All Fields]) OR “glaucoma”[All Fields] OR “macular degeneration”[All Fields] OR “cataract*”[All Fields] OR “vision impairment”[Title/Abstract] OR “vision loss”[Title/Abstract])) OR (“dual sensory impairment”[All Fields] OR ((“concurrent”[All Fields] OR “concurrently”[All Fields] OR “concurrents”[All Fields]) AND (“hearing”[MeSH Terms] OR “hearing”[All Fields] OR “hearings”[All Fields]) AND (“vision s”[All Fields] OR “vision, ocular”[MeSH Terms] OR (“vision”[All Fields] AND “ocular”[All Fields]) OR “ocular vision”[All Fields] OR “vision”[All Fields] OR “visions”[All Fields] OR “visioning”[All Fields])) OR “dual sensory loss”[All Fields])) AND (“Aged”[MeSH Terms] OR “Health Services for the Aged”[MeSH Terms] OR “elderly”[Title/Abstract] OR (“geriatrics”[MeSH Terms] OR “geriatrics”[All Fields] OR “gerontology”[All Fields] OR “gerontologie”[All Fields] OR “gerontology s”[All Fields]) OR “geriatr*”[All Fields] OR “older adult*”[Title/Abstract]) AND (1990:2021[pdat])
CINAHL	Health Literacy + Older Adults + Hearing	(MH “Health Literacy” OR “health literacy” OR MH “Health Knowledge” OR “health literate” OR MH “Health Education+” OR “health education” OR “health knowledge”) AND (MH “Aged+” OR “aged” OR MH “Gerontologic Nursing+” OR “elderly” OR geriatric* OR gerontolog* OR “older adult*”) AND (MH “Hearing Loss, Partial+” OR MH “Hearing Loss, Sensorineural+” OR MH “Hearing Loss, Noise-Induced” OR MH “Hearing Loss, High-Frequency” OR MH “Hearing Loss, Conductive” OR MH “Hearing Disorders+” OR “hearing loss” OR “hearing impairment” OR “persons with hearing impairment” OR “age related hearing impairment” OR “mixed hearing loss”)
CINAHL	Health Literacy + Older Adults+ Hearing + Vision OR Dual Impairment	(MH “Health Literacy” OR “health literacy” OR MH “Health Knowledge” OR “health literate” OR MH “Health Education+” OR “health education” OR “health knowledge”) AND (MH “Aged+” OR “aged” OR MH “Gerontologic Nursing+” OR “elderly” OR geriatric* OR gerontolog* OR “older adult*”) AND (MH “Hearing Loss, Partial+” OR MH “Hearing Loss, Sensorineural+” OR MH “Hearing Loss, Noise-Induced” OR MH “Hearing Loss, High-Frequency” OR MH “Hearing Loss, Conductive” OR MH “Hearing Disorders+” OR “hearing loss” OR “hearing impairment” OR “persons with hearing impairment” OR “age related hearing impairment” OR “mixed hearing loss”) AND (MH “lens diseases+” OR MH “retinal diseases+” OR MH “refractive errors+” OR hemianopsia OR MH “vision, subnormal” OR scotoma OR amblyopia OR “glaucoma” OR “macular degeneration” OR “cataract*” OR “vision impairment” OR “vision loss”) OR (“dual impairment” OR “dual sensory impairment” OR “dual sensory loss” or “concurrent hearing and vision”)
CINAHL	Health Literacy + Older Adults + Vision	(MH “Health Literacy” OR “health literacy” OR MH “Health Knowledge” OR “health literate” OR MH “Health Education+” OR “health education” OR “health knowledge”) AND (MH “Aged+” OR “aged” OR MH “Gerontologic Nursing+” OR “elderly” OR geriatric* OR gerontolog* OR “older adult*”) AND (MH “lens diseases+” OR MH “retinal diseases+” OR MH “refractive errors+” OR hemianopsia OR MH “vision, subnormal” OR scotoma OR amblyopia OR “glaucoma” OR “macular degeneration” OR “cataract*” OR “vision impairment” OR “vision loss”)

MeSH= medical subject heading, MH= CINAHL subject heading

Study Selection

Author LW imported results from each search into the reference management software Mendeley Version 1.19.8 (Elsevier Inc., New York, NY). Results were first organized by database and sensory loss type. Results were then combined into one file so duplicates could be removed, and the articles could be collectively screened. LW performed the article screening by abstract, or title when abstracts were not available. Articles noted to potentially meet eligibility criteria were shortlisted to be reviewed in full text and were then closely reviewed in full text by LW. Questions about article eligibility were discussed between LW, CB, and PC until consensus was reached.

Data extraction

Author LW extracted data from each study into a table of evidence including sensory loss type, author, year, country, study design, setting, sample size, participant characteristics, mean age, measure and definition of sensory loss, measure of health literacy, comparison, results, and study quality (See Table 2). Authors CB and PC reviewed and confirmed extracted data.

Table 2:

Table of Evidence and Study Characteristics

Author/Year	Country	Study Design	Setting	Sample size/participant characteristics	Measure and definition of sensory loss	Measure of health literacy	Comparison	Results	Quality Rating
Vision Loss
Juzych et al., 2008	United States	Cross-sectional	Outpatient practice/clinic	N=204 Mean age (SD): 66 years (13)Age range not reported. Participants treated for glaucoma for at least 1 year at clinic	Vision loss measured by visual field parameters (PSD and MD), average RNFL thickness on OCT. No definition of vision loss provided. Visual field parameters were analyzed continuously. Visual field parameters were used to indicate glaucoma severity in participants treated for glaucoma. *Of note, participants excluded if best corrected visual acuity was less than 20/50 in better eye	Measure: Reading comprehension section of TOFHLA Definition: Low health literacy defined as reading comprehension TOFHLA score of 0–30Adequate health literacy defined as reading comprehension TOFHLA score of 31–50	Health literacy across continuous vision measures	Participants with low health literacy showed a greater visual field loss on initial presentation (mean deviation [SD], −10.58 [9.3] dB) compared with adequate health literacy group (mean deviation [SD], −7.79 [6.9] dB; P = .02). Participants with low health literacy showed worse visual field parameters when comparing pattern SDs on the recent and the initial visual fields (pattern SD change [SD], 0.19 [2.5] dB in the poor health literacy group vs −0.7 [2.2] dB in the adequate health literacy group; P = .02).	Good 9/14 QA items
Warren et al., 2016	United States	Cross-sectional	Outpatient rehabilitation center and community	N=100 Mean age (SD): 81 years (6)Age range: 65–94 Participants from center for low vision rehabilitation and throughout community	Vision loss measured by ETDRS distance visual acuity chart. Vision loss defined as documented AMD diagnosis and distance visual acuity between 20/60 and 20/400 in better eye per ETDRS chart	Measure: TOFHLADefinition: Low (inadequate) health literacy defined as TOFHLA score of 0–59, marginal health literacy (60–74), adequate health literacy (75–100)	Health literacy across groups with and without vision loss	Vision loss group scored lower on composite test for standard time (Vision loss group 77.9[16.33] versus without vision loss 93.2[7.2]) p<.001) and unlimited time (Vision loss group 91.3[6.5] versus without 94.7[5.2]).	Poor 3/14 QA items
Fortuna, 2020	United States	Cross-sectional	Outpatient practice/clinic	N= 15 Mean age: 86 years (SD not reported)Age range: 67–96 Participants from a non-profit low vision clinic	Vision loss measured by unspecified distance visual acuity chart. Vision loss defined as a diagnosis of AMD and visual acuity between 20/60 and 20/1000 per unspecified distance measurement	Measure: S-TOFHLA Definition: Low (inadequate) health literacy S-TOFHLA score of 0–16, marginal health literacy (17–22), adequate health literacy (23–36)	Health literacy across vision loss severity groups	No significant differences in S-TOFHLA scores between three vision severity categories for timed and untimed testing conditions F(2,12)=2.768, p=.103; and F(3,27) = 1.853, p=.199	Poor3/14 QA items
Press et al, 2013	United States	Cross-sectional in an ongoing prospective study	Inpatient	N= 893 Mean age: not reported, 29% age 65 years or older*Age range not reported Participants were general medicine inpatients	Vision loss measured by unspecified (distance or near) Snellen visual acuity chart. No vision loss defined as visual acuity of at least 20/50 in one eye as measured by unspecified Snellen chart	Measure: BHLS (3 Likert scale questions, 0–4 score for each item) Definition: Low health literacy defined as a score of 2 or less on any question	Health literacy across groups with and without vision loss	Among patients with low health literacy on the BHLS, those with vision loss were at greater risk of low health literacy (126/213, 59%) than those without vision loss (258/680, 38%; p<.001)	Poor3/14 QA items
Schwennesen et al., 2019	Denmark	Cross-sectional	Outpatient practice/clinic	N=1425 Mean age: Overall mean age not reported. Mean age for group with vision loss: 63 years Mean age for group without vision loss: 53 years Age SD and range not reported Participants with type I diabetes from outpatient clinic	Vision loss measured by unspecified (distance or near) Snellen visual acuity chart. Vision loss defined as visual acuity of less than 0.5 as measured by unspecified Snellen chart	Measure: HLQ (includes 9 independent scales) Definition: Low health literacy not defined, but each scale produced a mean score with lower scores indicating lower health literacy	Health literacy across groups with and without vision loss	Participants with vision loss had a significantly lower mean score on ‘Ability to find good health information’ (3.52 versus 3.88, p<0.001) and ‘Understanding health information well enough to know what to do’ domains (3.48 versus 3.91, p<0.001) compared with the sighted respondents. Other domains not significant.	Poor 3/14 QA items
Jaffee et al., 2016	United States	Prospective Cohort	Inpatient	N= 1900 Mean age (SD): 54 years (19)Age range not reported Participants hospitalized on general medicine service	Vision loss measured by Snellen near visual acuity chart. No vision loss defined as at least 20/40 visual acuity in one eye as measured by near vision Snellen chart	BHLS (3 Likert scale questions, 0–4 score for each item) Definition: Low health literacy defined as a score of 2 or less on any question	Health literacy across groups with and without vision loss	Participants with vision loss were significantly more likely to have low health literacy than those without vision loss (34% versus 53.5%, p<.001)	Fair7/14 QA items
Hearing Loss
Tolisano et al., 2020	United States	Cross-sectional	Outpatient practice/clinic	N= 300 Mean age: not reported, Median age: 60Age range: (18–91) Participants evaluated at otology clinic practice	Hearing loss measured by PTA and word recognition scores (WRS)Hearing loss defined as: Class A: ≤30 dB pure-tone threshold and ≥70% speech discrimination Class B: >30dB, ≤50dB pure-tone threshold and ≥50% speech discrimination Class C: >50dB pure-tone threshold and ≥50% speech discrimination Class D: Any level pure-tone threshold, <50% speech discrimination	Measure: BHLS (3 Likert scale questions, 1–5 score for each item)Definition: Low (inadequate) health literacy defined as a score of less than 3 for each question, or a composite score of less than 9.	Health literacy across hearing loss severity groups	Class C or D hearing had higher risk of inadequate health literacy compared with Class A or B hearing (8.15 OR (3.42–19.37) p<0.0001)	Fair 6/14 QA items
Tran et al., 2021	United States	Cross-sectional	Tertiary academic medical center	N= 1376 Mean age (SD): 55 (17)Age range not reported Participants underwent audiometric testing at investigators institution	Hearing loss measured by PTA Hearing loss defined as PTA > 25dB. (Mild, 26–39dB; Moderate, 40–54dB; Moderate-Severe, 55–69 dB; Severe, 70–89 dB; Profound ≥90dB) *Although hearing loss is described categorically, hearing loss was analyzed continuously using PTA	Measure: BHLS (3 Likert scale questions, 1–5 score for each item)Definition: Low (inadequate) health literacy defined as a composite score ≤9	Health literacy across continuous hearing measures	Multivariable analysis: inadequate health literacy significantly associated with more severe hearing loss at initial presentation (adjusted mean PTA difference 5.38 dB, 95% CI 2.75 to 8.01) after adjusting for age, gender, marital status, education level, Medicaid coverage, language, and employment status	Fair7/14 QA items
Wells et al., 2020	United States	Cross-sectional	Phone survey to residents across New Jersey, Missouri, Texas and Washington	N= 19,223 Mean age: Not reported, All participants 65 years and older. Age range: Exact range not reported, although 65 to >85 Participants older adults with AARP Medicare Supplement plan by UnitedHealthcare Insurance Company	Hearing loss measured and defined by self-report questions: Which statement best describes your hearing without a hearing aid?  • Excellent or good and no hearing aid indicate no hearing loss  • A little trouble with no hearing aid indicates unaided mild hearing loss, and with hearing aid indicates aided mild hearing loss  • Moderate or a lot of trouble with no hearing aid indicates unaided severe hearing loss, and with hearing aid indicates aided severe hearing loss. In the past 12 months, have you worn a hearing aid at least 5 hours a week?	Measure: Single-item BHLS How confident are you filling out medical forms by yourself? Definition: Low health literacy defined as responses of a little bit, and not at all Adequate health literacy defined as extremely, quite a bit, and somewhat responses	Health literacy across hearing loss severity groups	Participants with unaided severe hearing loss 80% more likely to report low health literacy (OR 1.80 [CI 1.51, 2.15]), with unaided mild hearing loss (46%) (OR1.46 [CI 1.25, 1.71]), and aided severe hearing loss (41%) (OR 1.41 [CI 1.19, 1.69]). while those with aided mild hearing loss were not at increased risk for low health literacy	Fair 6/14 QA items

Quality Assessment

We assessed study quality using the NIH NHLBI Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies (2021). The tool provides 14 items for examination, with each item requiring an answer from the following options: yes, no, not reported (NR), or cannot determine (CD). Item results are not summed for an overall total; the appraiser determines overall study quality by considering potential bias based on item answers. This quality appraisal tool was selected as the group of studies meeting inclusion criteria were largely observational, analytical cross-sectional studies.

Results

Study Selection

We identified 2,745 articles from the database searches and 1 article through reference searching. 787 duplicate articles were removed prior to screening. We screened 1798 articles by abstract and 161 articles by title that did not have an abstract. Of the 1959 articles screened, we reviewed 46 full-text articles for eligibility. We excluded 37 of the 46 articles as the articles did not meet inclusion criteria—9 articles were not original quantitative research, 2 included the wrong population, 3 lacked a validated health literacy measure, and 23 did not evaluate the relationship between sensory loss and health literacy, including 15 descriptive only studies. Therefore, nine studies met inclusion criteria. Figure 1 includes a detailed PRISMA diagram.

Figure 1:

PRISMA Diagram of Search

Study Description: General Study Characteristics

Characteristics of included studies can be found in Table 2. Six articles examining the relationship between vision loss and health literacy^31–36 and 3 articles examining hearing loss and health literacy^37–39 were included. No articles were located examining the relationship between dual sensory loss and health literacy. Three studies included an exclusively older adult population of 65 years and older,^31,36,39 and the remaining studies had a mean or median age over 50 years as described in Table 2. Sample sizes ranged from 15 to 19,223 and settings varied. Four studies reported majority white participants,^31,36–38 three reported a Black or African American majority^32–34 and two did not report race in demographics.^35,39 Not all studies explicitly reported study design, however, based on the reported study methods, 8 of the 9 appear to be cross-sectional analyses and 1 was a prospective cohort study.³²

Of the 6 articles examining the relationship between vision loss and health literacy, 3 limited study populations to those with vision-related diagnoses,^31,33,36 1 focused on unspecified vision loss within a population of people with diabetes,³⁵ and 2 investigated general vision loss.^32,34 All articles examining hearing loss and health literacy evaluated general hearing loss without specifying hearing loss-related diagnosis. Most of the studies also included other primary study objectives.

Study Description: Health Literacy

The measurement of health literacy domains varied depending on the instrument used; some measured performance-based reading comprehension and numeracy,^31,33,36 another comprehensively measured a variety of domains³⁵ and the remaining articles measured the self-reported need for reading help and confidence with medical forms. The following instruments were used in the included articles: Test of Functional Health Literacy in Adults (TOFHLA),³⁶ the Short-TOFHLA,³¹ reading comprehension section only of TOFHLA,³³ Brief Verbal Screen Questions or the Brief Health Literacy Screen (BHLS),^32,34,37,38 single item BHLS,³⁹ and the Health Literacy Questionnaire.³⁵ Importantly, the 3 studies examining hearing loss and health literacy used an instrument that assesses health literacy related to the self-reported need for reading help and confidence with medical forms, and not verbal communication.⁴⁰ The scoring and categorization of health literacy status differed across the studies based on instrument scoring and analysis. Three studies categorized health literacy scores binarily as adequate and inadequate (also termed poor or limited),^33,38,39 and two studies included 3 health literacy categories as inadequate, marginal, and adequate.^31,36 Three studies only categorized a low literacy group and did not categorize those scoring above the low literacy level,^32,34,37 and one study did not use health literacy status categories.³⁵ The analysis of health literacy varied across the studies depending on categorical or continuous measurement. The definition of low health literacy varied significantly. For instance, Wells et al., (2020) used the single-item BHLS, and defined low health literacy based on a self-report response to a single question asking about confidence in filling out medical forms. Conversely, Fortuna et al., (2020) used the S-TOFHLA and defined health literacy status based on scores from a numeracy and a reading comprehension test.

Study Description: Vision Loss Definition and Measures

The measurement of vision loss varied as listed in Table 2; however, all studies used an objective measure. Vision measurement included: visual field parameters such as pattern standard deviation, mean deviation, Humphrey SITA-Fast, and retinal nerve fiber layer thickness;³³ distance visual acuity using the ETDRS acuity chart;³⁶ distance visual acuity using unspecified instrument;³¹ unspecified near or distance visual acuity measured by a Snellen eye chart;^34,35 and, near vision measured by the Snellen eye chart. Four articles evaluated health literacy between participants with and without vision loss, one article evaluated health literacy across vision loss severity groups,³¹ and another evaluated visual field parameters between health literacy groups.³³ The definition and categorization of vision loss varied depending upon methods and analysis. Most articles categorized vision binarily as sufficient and insufficient, one trichotomized vision loss as moderate, severe, and profound³¹ and one analyzed vision loss continuously based on vision measurements.³³ Of the 4 articles categorizing vision binarily, the definition of sufficient and insufficient varied. For instance, insufficient vision was defined as a distance visual acuity between 20/60 and 20/400 in the better eye as measured with the EDTRS chart,³⁶ and visual acuity of 0.5 or less measured with the Snellen chart.³⁵ Two articles only defined the cutoff for sufficient vision—including 20/40 in one eye measured with the near vision Snellen eye chart³² and at least 20/50 in one eye with the Snellen chart.³⁴ Fortuna (2020) defined the three VI categories based on distance visual acuity scores—moderate (20/70 to 20/160), severe (20/200 to 20/400), and profound (20/500 to 20/2000). Vision loss definitions are listed in Table 2.

Study Description: Hearing Loss Definition and Measures

Hearing loss was measured through objective measures such as pure tone audiometry,^37,38 word recognition scores³⁷ and subjective measures such as a self-report questionnaire.³⁹ Two articles compared health literacy across degree of hearing loss^37,39 and one evaluated health literacy across continuous audiologic scores.³⁸ One study classified hearing into 6 hearing loss severity groups (normal through profound hearing loss) based on pure-tone averages³⁸ while another classified hearing loss severity into 4 groups (Class A through Class D per the American Academy of Otolaryngology-Head and Neck Surgery) using pure-tone averages and word recognition scores.³⁷ The study using a subjective measure classified hearing loss into five hearing loss severity groups based on answers to two survey questions.³⁹ As an example of the different parameters for study categories, Tran et al. (2021) defined mild hearing loss as pure-tone averages of 26–39dB in the better ear; Tolisano et al. (2020) defined Class A hearing loss as a pure-tone threshold of less than or equal to 30dB and a speech discrimination percentage greater than or equal to 70% (this parameter was retrieved from the article’s references);^37,41 and, Wells et al. (2020) defined unaided mild hearing loss as the participant survey responses of a little trouble hearing and no reported hearing aid use. All 3 studies classified hearing loss by severity, however, severity classification differed. Study definitions of hearing loss are listed in Table 2. Two of the studies analyzed hearing loss categorically ^37,39 and one study analyzed hearing loss continuously based on pure-tone averages.³⁸

Quality Assessment

Using the NHLBI Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, 4 of the 6 vision studies were determined to be poor quality,^31,34–36 one of fair quality³² and one of good quality.³³ All 3 hearing studies were determined to be of fair quality. The cross-sectional design in most studies resulted in lower quality scores. Those rated as poor quality generally omitted methodological detail, and most did not report participation rate, provide sample size justification, examine different levels of exposure, or measure exposure more than once.

Relationship Between Vision Loss and Health Literacy

Of the 6 studies examining the relationship between vision loss and health literacy, 4 found a positive relationship between vision loss and low health literacy,^32–34,36 1 study found a positive relationship between vision loss and low health literacy in select health literacy domains³⁵ and the remaining study did not find evidence of a relationship between vision loss and low health literacy.³¹ As the methods and measurement of variables differed across studies, analysis and results varied. Juzych et al. (2008) found participants with low health literacy had more visual field loss on presentation compared to those with adequate health literacy (mean deviation [SD] (greater visual field loss) −10.58[9.3] dB vs −7.79 [6.9] dB, p=.02) and worse visual field parameters through pattern SD comparison on recent and initial visual fields (pattern SD change [SD], 0.19 [2.5] dB low health literacy group vs. −0.70 [2.19] dB in adequate health literacy group; p=.02).³³ Warren et al. (2016) found participants with vision loss had lower composite health literacy scores compared to those without vision loss under standard time (vision loss group 77.9 [16.3] vs non vision loss group 93.2 [7.2], p=<.001). Similarly, Jaffee et al. (2016) found participants with vision loss were more likely to have low health literacy than those without vision loss (53.5% vs. 34.0%, p<.001). Press et al. (2013) found that among participants with low health literacy, patients with vision loss were at greater risk of low health literacy compared to those without vision loss (126/213, 59% vs. 258/680, 38%, p<.001). Results from Schwennesen et al., (2019) found participants with vision loss had lower mean health literacy scores than those without vision loss in the domains ‘Ability to find good health information’ and ‘Understanding health information well enough to know what to do’ (3.52 vs 3.88, p<.001, and 3.48 vs 3.91, p<.001, respectively). Of note, Schwennesen et al. (2019) used a comprehensive health literacy assessment measuring several individually validated domains, therefore the detailed, domain-specific assessment may represent more precise information regarding the health literacy of those with vision loss. Results from Fortuna (2020) did not find any relationship between vision loss and health literacy but used a considerably smaller sample size of 15 participants with inconsistent use of optical assistive devices across severity groups.

Relationship between Hearing Loss and Health Literacy

All 3 studies examining hearing loss and health literacy found a positive relationship between hearing loss and low health literacy. Variation in study methods and variable measurement yielded differences in reported results. Tolisano et al. (2020) found participants with more severe hearing loss experienced an eight-fold higher risk of low health literacy compared to participants with less severe or mild hearing loss (28.6% vs 4.7%, p<.001). Tran et al. (2021) found low health literacy was significantly associated with greater hearing loss (adjusted mean pure tone audiometry difference 5.38 dB [95% CI 2.75 to 8.01]). Lastly, Wells et al. (2020) found participants with unaided severe hearing loss were more likely to report low or inadequate health literacy (OR 1.80, CI [1.51, 2.15]) as well as those with unaided mild hearing loss (OR 1.46, CI [1.25, 1.71]) and aided severe hearing loss (OR 1.41 CI [1.19, 1.69]). Importantly, Wells et al. (2020) found the use of hearing aids reduced the odds of low health literacy. In the hearing loss articles, the use of hearing loss severity classification and continuous audiologic values permitted the observation of graded associations, providing more robust evidence of empirical association.

Discussion

This systematic review is the first known to examine the evidence on the relationship between sensory loss and health literacy status. Overall, 6 of the 8 studies found a positive relationship between sensory loss and low health literacy,^{33,34,36–39} and 1 additional study found a positive relationship in select health literacy domains.³⁵ Findings suggest a positive relationship between sensory loss and low health literacy, which may provide insight into the role of low health literacy as a contributor to adverse health outcomes and increased healthcare utilization in older adults with sensory loss. The design and quality of studies, along with heterogeneity of evidence limits the understanding of this relationship and prevents causal inference. Despite study differences, our findings remain broadly consistent in supporting a positive relationship. Moreover, as the studies varied in setting and population characteristics such as race, this review’s findings may be considered generalizable.

Vision Loss and Health Literacy

Four of the 6 studies examining the relationship between vision loss and health literacy found a positive relationship between vision loss and low health literacy,^32–34,36 and 1 study found a positive relationship in select health literacy domains.³⁵ The reason for the positive relationship between vision loss and health literacy is likely complex due to the multifaceted nature of health literacy and ubiquitous effects of vision loss. At a fundamental level, people with vision loss are required to navigate a health care system largely dependent on adequate sight—from paperwork to self-care regimens. Compounding these difficulties, clinicians may not have the time or knowledge to sufficiently assist people with vision loss or provide accessible informational material.⁴² The use of written healthcare forms and limited time schedules have been found to influence health literacy amongst women with vision loss.⁴³ Broad cultural and societal factors extending beyond the physical impairment, including available support services and pervasive messages of disability affecting accommodations, may also impact health literacy for those with vision loss.^43,44 Furthermore, physiological factors may play a role; vision loss through reduced contrast sensitivity is a risk factor for cognitive decline,⁴⁵ and health literacy is also an indicator of cognitive function in older adults.⁴⁶ Thus, a link between vision loss and cognitive decline may affect health literacy in older adults with vision loss.

Notably, three studies included vision diagnosis-specific populations^31,33,36 which provide specific evidence for those populations but may not be as generalizable to the broad population of individuals with vision loss. Conversely, the studies with general vision loss populations do not discern visual differences between participants and may lack specificity. Most studies only measured one type of visual function—visual acuity—as the proxy measure for vision loss, with several studies only using distance acuity measures. This may provide an incomplete picture of the participants’ vision loss; especially as written health information is often provided to individuals requiring near vision. Additionally, the parameters defining sufficient versus insufficient vision categories varied considerably, which represents the challenge of measuring vision loss in research without a standard definition.⁴⁷

Hearing Loss and Health Literacy

All 3 studies examining the relationship between hearing loss and health literacy found a positive relationship between hearing loss and low health literacy.^37–39 The relationship between hearing loss and low health literacy is also likely complex. Adequate health literacy is dependent on the receipt of health information, frequently communicated verbally by health care providers. In qualitative studies examining the experience of individuals with hearing loss in primary care and hospital settings, participants reported significant health care communication difficulties with health care providers.^48,49 These difficulties likely present barriers to receiving, comprehending, and acting on health information. Older adults with hearing loss also reported feelings of frustration, embarrassment, and a desire to avoid inconveniencing staff.⁴⁸ Such feelings may reduce health knowledge and care abilities due to disengagement in care. Physicians also reported communication barriers, and the use of various communication approaches, at times misaligned with the desires of patients, signaling a lack of standard accommodations to support individuals with hearing loss.⁴² Feelings of shame, a desire to avoid burdening clinicians, and not receiving preferred accommodations further support the notion that cultural and societal factors such as disability perception may impact health literacy.

Furthermore, like vision loss, cognitive decline may mediate the relationship between hearing loss and health literacy. Studies have linked age-related hearing loss and cognitive decline,^6,7 and health literacy has been found to be an indicator of cognitive function in older adults.⁴⁶ Therefore, impaired cognitive processing—in addition to communication barriers—may affect health literacy in older adults with hearing loss. This point is underscored by the hearing loss studies’ use of a health literacy instrument assessing health literacy related to written health information, thus not capturing difficulties in verbal communication due to a hearing loss. However, Wells et al. (2020) found the use of hearing aids reduced the risk of low health literacy, indicating the use of hearing aids may play a role in improving health literacy of this population.

The methodological dissimilarities across the hearing studies are representative of the hearing loss literature. For instance, the hearing loss studies used both audiologic measures and self-report measures. Self-report measures have benefit in research regarding feasibility, however have been shown to lack accuracy and sensitivity compared to audiometric testing.⁵⁰ Moreover, age has been identified as a factor for failing to report moderately severe to severe hearing loss.⁵⁰ Thus, comparison of results between the studies should be interpreted accordingly.

Health Literacy

Similar to the measurement of hearing and vision loss, the variation in health literacy measurement limits conclusions and is representative of existing literature. Six health literacy instruments were used in the reviewed studies; thus, “health literacy” may vary substantially. The results of this review cannot be interpreted with a singular idea of health literacy as the concept was operationalized in a variety of ways. Moreover, the variation in administration and offered accommodations represent the lack of a standardized approach in administering health literacy assessments in populations with sensory loss.

Limitations

This systematic review has several notable limitations. Only 9 articles met the inclusion criteria resulting in a small body of evidence. Most articles were cross-sectional designs of poor to fair quality thus study bias may have impacted the collective results. Several of the studies had other primary objectives, thus were not designed to primarily examine the relationship between sensory loss and health literacy. Additionally, the review’s study question was specific to older adults and results were synthesized in this population context. However, few studies were exclusively limited to older adult populations, thus eligibility criteria included an expanded age criterion. Therefore, findings lack absolute specificity for the population of interest. Moreover, how vision and hearing loss were defined and measured differed, yielding results not directly comparable. This review also did not include studies published in languages other than English or in nonhealthcare databases.

Conclusions and Implications

This is the first known systematic review to evaluate the relationship between health literacy and sensory loss. Findings support a positive relationship between sensory loss and low health literacy in older adults and suggests the likelihood of low health literacy increases with the severity of hearing loss. As the number of older adults with sensory loss is expected to increase dramatically over the next four decades,^2,5 it is imperative for health care professionals to competently provide person-centered, quality care to this growing population. Older adults are disproportionately affected by chronic disease and have greater use of health services^51,52 requiring the navigation and comprehension of large amounts of health information. With sensory loss also widely prevalent in older adults, findings indicate a critical need for health care providers to be increasingly aware of sensory loss and its association with health literacy, to support effective health care communication practices. Providing suitable accommodations for those with vision or hearing loss is vital for imparting health information. Simple and effective strategies appropriate for sensory loss and low health literacy—such as facing a person when speaking, ensuring the space is well lit with reduced background noise, and verifying patient understanding after teaching—can improve health care communication. Basic devices, such as over-the-counter amplifiers and magnifiers, as well as more advanced technology, such as amplification and transcription apps on tablets or smartphones, also have the potential to enhance communication. Clinician knowledge of supportive communication strategies, assistive devices, and technological approaches coupled with intervention accessibility in the clinical setting may provide notable benefit. However, health care professionals must also consider that addressing low health literacy in older adults with sensory loss may require a more nuanced approach. Low health literacy in this population may be a result of, or complicated by, changes in cognition, resulting in a need for individualized approaches considering cognitive performance. A health literacy assessment—appropriately selected considering sensory loss, administration method, and relevant domains—can guide clinicians to provide targeted assistance to individuals.

This review supports future research. Well-designed longitudinal studies are recommended to better understand causality between sensory loss and health literacy and potential mediators such as cognitive function, as even mild cognitive impairment could impact health literacy measurement. Future research should also consider factors such as education level, socioeconomic position, and other social determinants of health. Studies evaluating the impact of sensory loss treatment on health literacy status are also recommended, extending the work of Wells et al. (2020). Lastly, research is needed to examine the impact of clinical interventions on low health literacy in older adults with sensory loss, addressing low health literacy as a modifiable determinant of health.⁵³

Table 3: Quality Appraisal.

National Institutes of Health (NIH) National Heart, Lung, and Blood Institute (NHLBI) Quality Assessment for Observational Cohort and Cross-Sectional Studies

	Research question/objective clearly stated	Study population (including time frame) clearly specified	Participation rate of eligible persons at least 50%	Subjects recruited from similar populations/Inclusion and exclusion	Sample size justification/power/variance and effect estimates	Exposure of interest measured prior to outcomes being measured	Timeframe sufficient to expect association between exposure and outcome	Different levels of the exposure as related to the outcome	Exposure measures clearly defined, valid, reliable, and implemented consistently	Exposure assessed more than once over time	Outcome measures clearly defined, valid, reliable, and implemented consistently	Outcome assessors blinded to the exposure status of participants	Loss to follow-up after baseline 20% or less?	Confounding variables measured and adjusted statistically for impact	Quality Rating
Vision Loss
Fortuna, 2020	Yes	No	NR	Yes	No	No	No	Yes	No	No	No	No	NA	No	Poor 3/14
Jaffee et al., 2016	Yes	No	NR	Yes	No	Yes	Yes	No	Yes	No	Yes	No	No	Yes,	Fair 7/14
Juzych et al 2008	Yes	Yes	Yes	Yes	Yes	No	No	Yes	No	Yes	Yes	Yes	NA	No	Good 9/14
Press et al., 2013	Yes	Yes	CD	CD	No	No	No	No	No	No	Yes	No	NA	No	Poor 3/14
Schwennesen et al., 2019	Yes	No	No	Yes	No	No	No	No	No	No	Yes	No	NA	No	Poor 3/14
Warren et al., 2016	Yes	No	NR	No	No	No	No	No	Yes	No	Yes	No	NA	No	Poor 3/14
Hearing Loss
Tolisano et al., 2020	Yes	Yes	NR	Yes	No	No	No	Yes	No	No	Yes	No	NA	Yes	Fair 6/14
Tran et al., 2021	Yes	Yes	NR	Yes	No	No	No	Yes	Yes	No	Yes	No	NA	Yes	Fair 7/14
Wells et al. 2020	Yes	Yes	No	Yes	No	No	No	Yes	No	No	Yes	No	NA	Yes	Fair 6/14

^*CD, cannot determine; NA, not applicable; NR, not reported