Changes in vision, such as the inevitable arrival of the need for reading glasses in middle age (presbycusis) are expected as a part of the normal aging process (Haegerstrom-Portnoy et al., 2002); however, there are eye diseases associated with aging that can further impair the visual abilities of older adults (Wong et al., 2014). Some visual functions change as a result of visual pathologies, such as age-related macular degeneration (AMD), glaucoma or diabetic retinopathy, all of which can cause low vision (Wittich and Gagné, 2016). Low vision (LV) has been described as a decline in visual functions that alters the ability to complete visual tasks, and that cannot be treated with corrective or contact lenses, or other surgical or medical interventions (Corn and Erin, 2010). The World Health Organization (2019) predicts that the number of individuals with AMD will increase 1.2-fold from 2020 (roughly 195 million) to 2030 (roughly 243 million). Interestingly, research indicates that visual decline due to AMD, and vision loss in general, are correlated with age-related cognitive decline, and persons with AMD are at higher risk of developing dementia due to Alzheimer’s disease (Rogers and Langa, 2010; Zhou et al., 2016; Nagarajan et al., 2022). The link between visual and cognitive functioning and aging has a long-standing knowledge base (Lindenberger and Baltes, 1994; Lindenberger et al., 2001); however, the majority of correlational explorations of vision and cognition have been conducted with population-based data sets (Hong et al., 2016) or have focused on specific sub-populations with cognitive or visual diagnoses [e.g., vision in patients with Alzheimer’s disease (AD; Kirby et al., 2010), or cognition in persons with AMD (Zhou et al., 2016)] that have received treatment or are being treated. Low vision rehabilitation is a service that aims at improving daily living by providing techniques to use remaining intact vision. We are unaware of any studies on the effect of low vision rehabilitation on cognition that have been able to include participants with low vision (e.g., visual acuity below 20/60) that had not (yet) received rehabilitation services. A recent longitudinal study focused on functional improvement in activities of daily living in veterans with low vision, with or without cognitive impairment, but the study did not assess cognition pre- and post-rehabilitation (Whitson et al., 2020). The present pilot study aimed to explore the relationship among sensory and cognitive variables, specifically in older adults who had not yet received low vision rehabilitation, thereby presenting an opportunity to better understand the relationship among their pre-rehabilitation sensory-cognitive abilities. This understanding is required for future studies that will explore the effect vision rehabilitation may have on cognition in older adults with low vision (Wittich et al., 2021).

As a result of the normal aging of the visual system, near visual acuity is expected to decrease somewhat, making the reading of small print more challenging (Pierscionek and Weale, 1995). Similarly, aging affects cognitive abilities, such as memory and processing speed (Park and Gutchess, 2016), and a decline in cognitive function is expected. In addition, cognitive pathologies, such as AD and vascular dementia, are two of the most predominant forms of dementia, causing significant changes in cognition (World Health Organization, 2017).

Several studies have linked changes in visual function (e.g., visual acuity, reading acuity) to changes in cognitive function (Rogers and Langa, 2010; Dupuis et al., 2014; Zhou et al., 2016; Davies-Kershaw et al., 2018; Zheng et al., 2018; Ehrlich et al., 2021). For example, cognitive impairment, as measured by on a score of lower than 28 on the Mini Mental State Examination (MMSE), is related to slower reading speed on the Minnesota Low Vision Reading Test (MNRead; Swenor et al., 2016). Similarly, impairment in visual acuity has been linked to lower scores on the Montreal Cognitive Assessment (MoCA; Dupuis et al., 2014), a screening tool designed to identify persons at risk for mild cognitive impairment. Additionally, individuals with mild cognitive impairment and AD have higher rates of reduced reading acuity than individuals with subjective cognitive decline (Wittich et al., 2019). In a meta-analysis, the presence of AMD has been linked to lower scores on various cognitive tests (i.e., Mini-Mental State Examination, Mini-Cog test, Trail Making Test A; Zhou et al., 2016).

Several studies have found vision-related abnormalities in individuals with AD. Visual deficits (e.g., difficulty reading, loss of contrast sensitivity) are commonly found in AD (Lee and Martin, 2004), and visual complaints are often reported by AD patients in the early stages of the disease and may precede the memory decline (Ikram et al., 2012). In addition, a decrease in the visual field and/or contrast sensitivity, as well as fixation problems, are common in AD patients (Ikram et al., 2012). A longitudinal study found that self-reported low vision was a risk factor for AD (Davies-Kershaw et al., 2018). Moreover, this relationship between AD and visual deficits is also present in the brain at the structural level, whereby the topological organization of higher-level visual networks is altered in individuals with AD and mild cognitive impairment (Deng et al., 2016).

Furthermore, several studies focusing on functional outcomes explored the link between changes in vision (e.g., visual acuity, contrast sensitivity) and changes in cognition (e.g., global cognition, executive functions, psychomotor speed). Longitudinal studies have demonstrated an association between low vision and cognitive decline over time, whereby the severity of the decline in visual acuity over 8 years, as measured by the ETDRS chart (Early Treatment of Diabetic Retinopathy Study), is linked to the severity of the cognitive decline at the 8-year follow-up, as measured by the MMSE (Zheng et al., 2018). Another study showed that low vision is associated with the transition from normal cognition to cognitive impairment or dementia, using Digit Symbol Substitution Test and the Modified MMSE), to measure cognition (Ehrlich et al., 2021). A longitudinal study assessing multiple aspects of visual functioning (e.g., contrast sensitivity, visual acuity, and stereo acuity) found that impairments in these measures of vision were associated with increased risks of a decrease in psychomotor speed, worse executive functioning, and general cognitive decline over 9 years (Swenor et al., 2019). A risk factor for cognitive decline and AD is uncorrected self-reported low vision (Rogers and Langa, 2010), while wearing glasses and having good visual acuity can be protective against cognitive decline (Spierer et al., 2016).

Many mechanisms have been postulated to explain this link between sensory and cognitive decline. First, the information degradation hypothesis states that neurobiological processes (e.g., AMD) weaken the strength of the perceptual signal, which, in turn, negatively affect perceptual and cognitive processing (Monge and Madden, 2016). In the case of AMD, the visual decline may cause a decrease in the stimulation, thereby resulting in cognitive decline. Second, the sensory deprivation hypothesis states that a persistent absence of adequate sensory input will create neuronal atrophy and will later result in cognitive decline (Clay et al., 2009). In the case of AMD, the reduced visual input due to visual decline may create neuronal atrophy, meaning that cognitive decline may result later because of AMD. Third, the cognitive compensation hypothesis states that cognitive functions could be used to compensate for the visual decline, therefore monopolizing the cognitive resources and causing cognitive decline (Roberts and Allen, 2016). In the case of AMD, this could mean that cognitive resources, such as attention, could be used to compensate for vision loss. Therefore, not all cognitive functions are available for higher-level tasks. For example, as attention is a key function in the encoding process, this compensation could result in less in-depth encoding, leading to memory decline.

Another hypothesis is the common cause hypothesis, which states changes in sensory and cognitive ability are due to a single common cause, such as the aging brain (Kiely and Anstey, 2015). Other hypotheses have also been proposed to explain the relationship between concomitant changes in sensory and cognitive functions. Social participation has been proposed as a key factor in cognitive health. For example, individuals with vision loss might fear falls when going outside and prefer not to attend social event for this reason. This reduced participation might be followed by a reduction in cognitive capacities (Bourassa et al., 2015).

Recently, some anatomical studies have linked AMD and AD (Dentchev et al., 2003; Chang et al., 2014; Ratnayaka et al., 2015). The brain and the retina share many similarities, such as the same embryological origin, as well as some anatomical and physiological features (Ikram et al., 2012). Chang et al. (2014) presented evidence that the three well-known AD biomarkers—protein amyloid-ß, senile plaques, and neurofibrillary tangles, are also present in the retina of AD patients. Another study linked amyloid-ß deposits in the retina to AMD (Dentchev et al., 2003). These discoveries are an important step in understanding the critical link between AMD and AD.

According to the first three hypotheses, the degradation of the sensory input is proposed to be linked to cognitive decline. The first two hypotheses state that the degradation of the sensory input is causing the degradation of cognition. Therefore, focusing on ways to reinstate the visual input in AMD patients could theoretically preserve or potentially improve cognitive functioning. According to the third hypothesis, reducing the effort needed to see and read could reduce the cognitive demands for tasks involving reading, and more cognitive resources could be allocated to higher-level tasks. Therefore, in line with all three hypotheses, low vision rehabilitation should be a way to preserve or even improve cognitive functioning in patients with AMD. At present, little is known about any relationship among sensory and cognitive variables before the vision rehabilitation process in persons living with AMD.

In Quebec, individuals with vision loss have access to rehabilitation services and assistive devices provided by the government at no cost to the client (Government of Quebec, 2022). Eligible individuals can undergo low vision rehabilitation to maximize their residual vision and learn strategies to compensate for their vision loss (Gordon et al., 2015). These services can include adaptations of the client’s physical environment to ensure proper lighting and adaptive techniques for reading, instruction in the use of assistive devices to facilitate visual activities, and other considerations that might be appropriate for the client. Low vision rehabilitation has been linked to an improvement in quality of life and participation in activities of daily living (Binns et al., 2012). However, to our knowledge, there are currently no data available that evaluate the impact of low vision rehabilitation on cognition in older adults.

The Institutional Review Board approval for this study was obtained from the Centre de recherche interdisciplinaire en réadaptation du Montréal métropolitain (CRIR #1284-1217). Additional details about the larger protocol context, within which these pilot data were collected, have been published elsewhere (Wittich et al., 2021).

All tests were selected because they are suited for individuals with vision impairment (i.e., they do not depend on vision), are available and validated in French and in English, and have acceptable psychometric properties. Most testing sessions took place in the participants’ home. A demographic questionnaire was used to collect basic information about the participants, such as their age, level of education and living circumstances. The questionnaire also contained items about their reading habits, both before and after the onset of their visual impairment. In addition, the Depression, Anxiety and Stress Scale (DASS 21; Lovibond and Lovibond, 1995) was used to assess the mental health of participants over the past week (Henry and Crawford, 2005) because it has good psychometric properties when used with older adults (Gloster et al., 2008).

Prior to the analysis, the data were thoroughly screened for any missing or extreme values. When possible and/or suitable, the missing values were replaced by the mean of the sample or the mean of the participant (for questionnaires with multiple items). Two extreme values were removed from the data: one from the CDTT test, whereby the results indicated that the participant had an extremely severe hearing impairment that did not correspond to the communication experience with the participant and was, therefore, more likely a headphone malfunction. The second extreme value was a MoCA score of 4. Since the participant fell asleep during the MoCA, we judged that his result was not an adequate representation of his cognitive capacities. As for the other tests completed by this participant, they were included in the analysis as he was fully awake during this part of the testing, and his scores did not fall more than three SD from the group mean. Sample sizes for all available measures are provided in Table 2. Small samples (e.g., scores on the IReST) are explained by the participants’ inability to read because they had not yet received any vision rehabilitation. Missing data play a potentially important role in the assessment of cognition in persons with sensory impairment (Abraham et al., 2023); however, we did not observe any noteworthy patterns in missing cognitive measures, given that they were all chosen to accommodate the presence of visual impairment.

Correlations among cognition and demographic variables can be found in Table 4. Age was significantly negatively correlated with the full MoCA score (r = −0.365, p < 0.05), the RAVLT acquisition (r = −0.656, p < 0.001), the RAVLT delayed recall (r = −0.595, p < 0.001) and the RAVLT recognition (r = −0.461, p < 0.01). There was also a significant positive correlation between education and RAVLT – acquisition (r = 0.409, p < 0.05).

The purpose of the present pilot study was to characterize the sensory and cognitive status of adults with AMD referred for visual rehabilitation. Our first objective was to assess the correlations between sensory and cognitive functions in our participants before controlling for variables known to be important in the context of cognition. The second objective was to examine which of these correlations would remain significant once established variables that influence cognition are statistically removed (i.e., age and education).

First, the association between contrast sensitivity and word recognition, as measured by the RAVLT, remained significant after controlling for age and education. This result was surprising given our limited sample size, given the reduction in statistical power by controlling for additional variables. This finding emphasizes the importance of contrast sensitivity as a variable in sensory-cognitive relationships in aging, which has previously been highlighted in the scientific literature. Globally, lower contrast sensitivity has been associated with a higher risk of mild cognitive impairment and dementia in older women, as assessed by an expanded neuropsychological tests battery and a panel of clinical experts (Ward et al., 2018). Contrast sensitivity has also been identified as a measure that is likely to detect early AD-associated changes in groups with subjective cognitive decline, amnestic mild cognitive impairment, and AD (Risacher et al., 2013). Moreover, impairments in contrast sensitivity as measured by the Pelli–Robson chart (similar in its structure to the MLCS used in the present study) are associated with a decline in global cognition as measured by the Modified Mini-Mental State Examination (Swenor et al., 2019).

Furthermore, episodic memory is an important cognitive function in sensory-cognitive aging, as it tends to decline both in normal and pathological aging. Our result is also particularly interesting in that sense, as word recognition processes are usually the ones that are the most preserved in normal aging (Perlmutter, 1979). Compared to free recall and cued recall, recognition facilitates information retrieving by presenting all the encoded information within distractors. Therefore, the recognition process helps differentiate between difficulties in encoding in comparison to difficulties retrieving information. Our results replicate studies that indicate that contrast sensitivity could be sensitive to subtle changes in cognition, specifically in the encoding process, in non-demented older adults (Risacher et al., 2013; Ward et al., 2018; Swenor et al., 2019).

One other correlation remained significant after controlling for age and education: the association between the use of visual aids and global cognition, as measured by the blind version of the MoCA. Even though our data were collected before the beginning of the low vision rehabilitation process, many participants were proactive in looking for devices that could facilitate reading and were already using various visual aids, the most popular being a magnifier. Therefore, this result may indicate that individuals already using visual aids, even before the beginning of the formal rehabilitation process, may have better global cognition, as measured by the MoCA (blind version). However, as our data are correlational, this could also mean that individuals with better baseline global cognition are more proactive, seeking out the use of visual aids even before the beginning of the formal rehabilitation process. This is also in line with the current literature, as a recent study demonstrated that the use of visual aids demonstrated a potential effect on slowing cognitive decline in a long-term care facility environment (Kwan et al., 2022).

Finally, our results corroborate findings in the scientific literature regarding the association between low vision and cognitive decline. We found that older adults with low vision have significantly poorer cognitive functions (e.g., episodic memory, processing speed, global cognition) compared to normative values. In line with previous research (Zhou et al., 2016; Zheng et al., 2018; Lee et al., 2020), these results indicate that the occurrence of vision loss in non-demented individuals is associated with poorer global cognition, memory, and executive functions.

The present results are in concordance with some postulated mechanisms explaining the link between sensory and cognitive processes. Our results could be explained by the information degradation hypothesis, which states that neurobiological processes, such as vision loss, diminish the strength of the perceptual signal, which negatively affect the perceptual processing and, therefore, cognitive processing (Monge and Madden, 2016). As this hypothesis does not postulate an association over time, it is possible to examine it using cross-sectional data like ours. It appears in our sample that, as compared to normative data, our low vision participants have significantly lower scores in global cognition, memory (acquisition and delayed recall), and executive functions (processing speed). Moreover, our results show that only 7.9% of our sample passed the MoCA, and 34.2% passed the MoCA-Blind. These results indicate that roughly 66% of our sample could be at risk for cognitive impairment, whereas the estimated prevalence of cognitive impairment in the Canadian population is 25% in adults 85 years old and older (Canadian Institute for Health Information, 2021).

The sensory deprivation hypothesis states that a persistent absence of adequate sensory input creates neuronal atrophy and later results in cognitive decline (Clay et al., 2009). The cognitive compensation hypothesis states that cognitive functions could be used to compensate for the visual decline, therefore monopolizing the cognitive resources and causing cognitive decline (Roberts and Allen, 2016). However, both these hypotheses require prospective data. Thus, we cannot speculate using our cross-sectional results. Our data indicate that individuals that are already using visual assistive devices before their visual rehabilitation have significantly better global cognition scores (both versions of the MoCA) and better delayed recall than those who do not already use assistive devices. As of now, our results align with only one of these proposed mechanisms, as our participants may have self-protected their cognition by initiating the rehabilitation process. Eventual prospective data are needed to assess the effect of time and rehabilitation services on cognitive functions, as planned in our larger protocol (Wittich et al., 2021).

The results of this pilot study clearly emphasize the importance of assessing the sensory abilities of older adults with low vision together with evaluating their cognitive abilities. Our participants with AMD demonstrated lower cognitive abilities than what would be expected from their sighted counterparts, even when choosing testing materials that did not rely on functional vision. A larger sample and prospective data are needed to assess the potential effect of low vision rehabilitation on cognition in older adults with AMD. The next step will be to implement the full protocol of this research project (Wittich et al., 2021), thereby expanding our understanding of sensory-cognitive aging and the role sensory rehabilitation can play in preserving cognitive function.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Centre de recherche interdisciplinaire en réadaptation du Montréal métropolitain (CRIR #1284-1217). The patients/participants provided their written informed consent to participate in this study.

GA contributed to conceptualization, formal analysis, investigation, methodology, validation, writing the original draft, and writing—review and editing. NP, AtJ, AaJ, SJ, VB, and EK contributed to conceptualization funding acquisition, formal analysis and data interpretation, investigation, methodology, resources, writing—original draft, and writing, review, and editing. WW led the conceptualization, data curation, funding acquisition, investigation, methodology, project administration, resources, supervision, validation, writing, review and editing. All authors contributed to the article and approved the submitted version.

This study was financially supported by the Fonds de recherche du Québec—Santé (Programme DMLA #252235), in partnership with the Fondation Antoine-Turmel and the Réseau de recherche en santé de la vision, and the Canadian Institutes for Health Research #169713 with a patient-oriented project grant for early career investigators.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.