Abstract
Purpose.:
The use of patient-reported outcome (PRO) measures to assess self-reported difficulty in visual activities is common in patients with impaired vision. This study determines the visual and psychosocial factors influencing patients' responses to self-report measures, to aid in understanding what is being measured.
Methods.:
One hundred visually impaired participants completed the Activity Inventory (AI), which assesses self-reported, vision-related activity limitation (VRAL) in the task domains of reading, mobility, visual information, and visual motor tasks. Participants also completed clinical tests of visual function (distance visual acuity and near reading performance both with and without low vision aids [LVAs], contrast sensitivity, visual fields, and depth discrimination), and questionnaires assessing depressive symptoms, social support, adjustment to visual loss, and personality.
Results.:
Multiple regression analyses identified that an acuity measure (distance or near), and, to a lesser extent, near reading performance without LVAs, visual fields, and contrast sensitivity best explained self-reported VRAL (28%–50% variance explained). Significant psychosocial correlates were depression and adjustment, explaining an additional 6% to 19% unique variance. Dependent on task domain, the parameters assessed explained 59% to 71% of the variance in self-reported VRAL.
Conclusions.:
Visual function, most notably acuity without LVAs, is the best predictor of self-reported VRAL assessed by the AI. Depression and adjustment to visual loss also significantly influence self-reported VRAL, largely independent of the severity of visual loss and most notably in the less vision-specific tasks. The results suggest that rehabilitation strategies addressing depression and adjustment could improve perceived visual disability.
Patient-reported outcome (PRO) measures are of increasing importance in vision science and ophthalmology. Such assessments are used to determine the effect of interventions and to guide rehabilitation in the visually impaired by identifying areas of difficulty.
1,2 A wide range of PRO instruments is available to assess health-related or vision-related quality of life and vision-related difficulty in activities of daily living (ADL) (reviewed in Refs.
3,
4). In this study, we considered the aspect of self-report concerned with the perceived difficulties experienced in ADL as a result of vision loss. To better understand what PRO instruments are assessing, we asked how both visual and nonvisual factors influence self-reported, vision-related activity limitation (VRAL) of the visually impaired.
It has been shown that self-reported VRAL as measured by items in common visual function assessment instruments (or questionnaires), represents a unidimensional construct, or the measurement of a single attribute.
2,5,6 The Activity Inventory (AI) is an adaptive instrument designed to provide an individualized assessment of difficulties for a visually impaired respondent.
6 The AI consists of a hierarchal structure in which specific cognitive and motor visual tasks (e.g., pouring or mixing without spilling) underlie more global goals (e.g., preparing meals). Disabilities (or activity limitations, according to the World Health Organization's International Classification of Functioning [WHO ICF]
7 ) occur when an individual reports abnormal difficulties in achieving important goals and difficulties achieving a goal are said to depend on the difficulty experienced in the tasks that underlie each goal.
6
Although self-reported VRAL represents the functional limitations and resultant disability caused by visual impairment, only a modest relationship has been seen between self-report and clinically measured visual function (previously reviewed in Ref.
8). Approximately 50% of the variance in reported difficulty can be explained by clinical measures of visual function including acuity, contrast sensitivity, and visual fields.
8 –12
One possible explanation of the modest relationship between clinical and self-reported visual function may reflect that most instruments ask respondents to report their difficulties under their usual day-to-day conditions, which would include the use of any compensatory strategies such as low-vision aids (LVAs). However, clinical tests of visual function are usually performed under standardized conditions using only refractive correction (either habitual or best corrected). It is possible that despite a decline in clinical visual function, individuals can fully compensate for the decline by using strategies such as LVAs. These patients are said to exhibit preclinical disability as they are at risk of disability, but do not perceive difficulties due to their use of compensatory strategies.
13 However, it is not clear whether self-reported VRAL best reflects the severity of vision loss (clinical function without aids) or the visual function attained when using LVAs.
Factors other than clinical visual function, represented within the WHO ICF, have also been suggested to influence the self-reported VRAL of the visually impaired.
14,15 Depression has often been associated with worse self-reported function in the visually impaired, sometimes independent of the severity of vision loss as characterized by visual acuity.
16 Better social support has been associated with better ADL function in non–vision-specific research,
17,18 yet greater instrumental support from family members has correlated with worse reported VRAL in the visually impaired.
19 Better adaptation and adjustment to vision loss has been significantly associated with fewer reported functional limitations in ADL as a consequence of vision loss
19 and with greater improvement in reported VRAL after low vision rehabilitation.
20 Personality may also affect self-reported function. Individuals higher in the personality trait of neuroticism have been found to have significantly worse mobility function
21 and poorer self-reported function in ADL
18 in non–vision-specific research.
The purpose of this study was to characterize the relationship between self-reported VRAL as measured by the AI and not only a range of visual function measures, but also nonvisual psychosocial factors in a sample of adults with visual impairment. The purpose was to assess the relative roles of these factors in determining self-reported VRAL, such that what PROs are measuring can be better understood.
All data were double entered and corrected for errors before data analysis. Rasch analysis
42 was conducted using Winsteps version 3.69.1
43 on responses to all self-report instruments to provide person measure estimates for each construct. Person measures were derived from the AI for overall self-reported VRAL at goal and task level and for each functional domain.
Univariate analyses were first undertaken to explore the demographic, visual function, and psychosocial variables. Bivariate analyses in the form of linear correlation coefficients were then conducted to investigate the association between the predictor variables and self-reported VRAL. Next, significantly correlated variables were entered into separate demographic, visual function, and psychosocial factor stepwise regression analyses. Finally, the variables identified as significant predictors were entered into an overall multiple regression model. Conducting separate regression analyses initially and then together in overall regression analyses allowed the amount of unique variance of self-reported VRAL explained by visual and nonvisual factors to be calculated in addition to determining the degree of shared variance they explain.
The results of the study indicate that the nonvisual psychosocial factors of depression and adjustment can explain unique variance in self-reported VRAL not accounted for by the severity of vision loss as represented by clinical visual function. The visual factors that are associated with self-reported difficulties correspond to visual function without, as opposed to with, LVAs. Adjustment, but not depression, is significantly associated with the degree of vision loss but only when self-reported function is not considered.
The specific clinical visual functions best explaining self-reported VRAL are visual acuity and reading performance without LVAs, contrast sensitivity, and a measure of visual fields. These visual functions have all previously been seen to significantly correlate with self-reported function.
8 –12 As acuity without LVAs was the strongest predictor of self-reported VRAL in most instances, the findings of previous studies in which only visual acuity is considered to represent vision loss severity can be more strongly regarded.
16
The AI asks respondents about difficulty with tasks even when wearing glasses and using magnifiers or other LVAs. We hypothesized that visual acuity with LVAs would better predict reported activity limitation than standard clinical measures of acuity. Few participants used LVAs for distance tasks, also seen elsewhere,
51 and so we were able to test this prediction only for reading ability. Contrary to the hypothesis, self-reported VRAL in all domains was better predicted by visual function without LVAs.
It is understandable that reading performance with LVAs may not be a good representative of function in activities other than reading. However, this fails to explain why reading function with LVAs does not correlate well with reported habitual reading performance. As the study appointments followed low vision support with a separation of a minimum of 2 weeks, it is possible that participants were not accustomed to using any newly prescribed aids, affecting their perceived habitual limitations. Allowing a greater period to habituate with any aid may strengthen the relationship between self-reported VRAL and magnifier-aided visual function.
However, all participants regularly used some form of reading aid. In addition, magnifier-aided near reading performance was better than function without aids, suggesting proficiency of use (median x-height values with LVAs [
Table 4] correspond to print size of 0.49 logMAR [CPS] and 0.12 logMAR [acuity] viewed at 40 cm, smaller than the equivalent assessments without LVAs: 1.00 logMAR and 0.81 logMAR, respectively). Therefore, at least when considering responses to the AI, it may also be that despite the use of aids, difficulty is still reported, with the difficulties reflective of the severity of vision loss as represented by standardized clinical visual function, as opposed to function with LVAs. Further, although all participants were instructed and reminded when required to report their difficulties when using any LVAs such as magnifiers, it is possible that individuals are more often without their magnifiers than using them, and this is what is reflected in self-reported visual function.
It should be noted that in the present study and others,
11,52 clinical visual function was best associated with self-reported VRAL in more vision-specific items, notably reading tasks (50% unique variance explained;
Table 9). Reading items include tasks such as reading newspaper articles, which are closely reflected by clinical assessments such as reading performance and as a result there is perhaps less chance of individual interpretation and influence from psychosocial factors (6% unique variance explained). A greater influence of nonvisual psychosocial factors was seen when self-report included fewer vision-specific items, which may be open to greater individual interpretation, such as many of the mobility and visual motor items (up to 17% unique variance explained). Examples of such items include arranging and using transportation (mobility), and listening to the radio and using a computer (both visual motor). The visual requirements for these tasks are at face value less comparable to the clinical assessments of visual function resulting in a weaker relationship with clinical visual function (28%–33% unique variance explained). Therefore, when using PROs of ADLs the choice of questions or instrument should be driven by its intended purpose, depending on whether the aim is to reflect visual function (use vision specific tasks) or to give an overview of perceived disability (use less vision-specific tasks).
With reference to the psychosocial factors, depression has been significantly associated with self-reported VRAL,
16,19,53 explaining up to 20% variance after regression analyses.
54,55 The results of the present study demonstrate that, except for reported reading function, depression explains variance in self-reported responses not accountable for by visual impairment severity, including as much as 17% of variance in self-reported mobility function.
Adjustment to vision loss depends on the psychosocial profile of an individual, although the exact process of adjustment is still largely unknown
40,56 and individuals can vary enormously in their reactions to vision loss.
57,58 Adjustment in the context of the present study refers to the unidimensional latent construct that involves aspects of self-esteem, acceptance, locus of control, attitudes, and self-efficacy, as measured by the 19-item AS-WAS.
40 The results indicate, consistent with previous studies,
19,59 that adjustment to vision loss is significantly associated with self-reported VRAL. The association between adjustment and self-reported limitation is not entirely independent of the severity of vision loss, but is only apparently related to the severity of vision loss due to the functional limitations caused by the visual impairment rather than with the degree of vision loss itself, since the significant relationship between adjustment and clinical visual function is lost when self-reported VRAL is controlled. Therefore, greater vision loss does not necessarily indicate poorer adjustment. Clinically this is important as although greater vision loss may be related to poorer adjustment the effects could be limited by reducing the functional limitations through rehabilitation.
Despite being significantly associated with self-reported VRAL (
Table 6), the effect of social support is lost when the levels of depression and adjustment are also considered (
Table 8). Together with the findings of others,
60 it appears that social support does not directly influence self-reported activity limitation; rather it is depression and adjustment to which social support is related.
59,61 Similarly, and in agreement with other studies,
62,63 the significance of personality, namely neuroticism, in influencing self-report is also lost when depression and adjustment are considered. However, neuroticism may be related to depression
64,65 which does predict self-reported VRAL.
Although low vision rehabilitation often seeks to improve visual function with the use of optical and adaptive devices,
66 the results of the present study suggest that difficulty in ADL may still be perceived despite implementing compensatory strategies such as LVAs. As vision loss is generally irreversible, and since depression and aspects in the adjustment process such as self-esteem and self-efficacy are dynamic,
67 it may be advisable to also target psychosocial functioning to help alter perceptions of visual function with rehabilitation. Indeed, improvements in depression and adjustment post rehabilitation have paralleled improvements in self-reported VRAL.
68 –71 Nonetheless, it appears the next step in research is to study multiple time points, including the impact of different interventions
72 and structural equation modeling techniques,
73 to further investigate the importance of depression, adjustment, and severity of vision loss on self-reported limitations as identified in the present study.