Patient-Centered Outcome Measures to Assess Functioning in Randomized Controlled Trials of Low-Vision Rehabilitation: a Review

Patient (2017) 10:39–49 DOI 10.1007/s40271-016-0189-5

REVIEW ARTICLE

Patient-Centered Outcome Measures to Assess Functioning in Randomized Controlled Trials of Low-Vision Rehabilitation: A Review

1,2,3 4 2,5,6 1,2,3 Joshua R. Ehrlich • George L. Spaeth • Noelle E. Carlozzi • Paul P. Lee

Published online: 5 August 2016 Ó Springer International Publishing Switzerland 2016

Abstract Low-vision rehabilitation (LVR) aims to interventions across studies. Selecting valid outcome mea- improve the functioning of patients with chronic uncor- sures that are both relevant to LVR goals of specific patient rectable visual impairment. LVR is inherently a patient- populations and that measure functioning across a range of centered intervention since its approach and goals are dic- visually demanding tasks could improve the ability to detect tated by the needs and abilities of each individual patient. the effect of LVR and to compare rehabilitation strategies. Accordingly, it is essential to have patient-centered out- There are advantages and limitations to the use of both come (PCO) measures to assess and compare the efficacy patient-reported and performance-based outcome measures, and effectiveness of low-vision interventions; however, and additional work should be undertaken to explore the there is a lack of evidence on the effectiveness of LVR relationship between these modes of assessment, as well as interventions. We reviewed the literature in order to identify strategies for optimally integrating these approaches. randomized controlled trials (RCTs) in the field of LVR and Careful selection of outcome measures in the design of the outcome measures used to assess patient functioning in future RCTs in LVR may lead to improved understanding of these trials. We identified 15 RCTs of LVR that employed the effectiveness of LVR and, ultimately, to improved nine unique patient-reported, five unique performance- functioning of patients with low vision. based, and one hybrid (combined patient-reported and performance) outcome measures. Since these trials used distinct tools to assess patient functioning, it is difficult to Key Points for Decision Makers compare the effectiveness of competing rehabilitation Numerous outcome measures have been used in randomized controlled trials of low-vision rehabilitation (LVR) and this has made it difficult to & Joshua R. Ehrlich [email protected] compare competing rehabilitation interventions.

1 Department of Ophthalmology and Visual Sciences, Patient-reported and performance-based outcome University of Michigan, 1000 Wall Street, Ann Arbor, MI measures both have distinct advantages and 48103, USA limitations when used to assess functioning in LVR. 2 Institute for Healthcare Policy and Innovation, University of Additional work is needed to better understand the Michigan, Ann Arbor, MI, USA relationship between patient-reported and observed 3 Center for Eye Policy and Innovation, University of performance, and how these types of instruments Michigan, Ann Arbor, MI, USA may complement one another. 4 Glaucoma Research Center, Wills Eye Hospital, Existing outcome measures may not be relevant to Philadelphia, PA, USA the rehabilitation goals of some sizeable patient 5 Center for Clinical Outcomes Development and Application populations with low vision. Future work and (CODA), University of Michigan, Ann Arbor, MI, USA resources should be dedicated to ensuring that valid 6 Department of Physical Medicine and Rehabilitation, outcome measures exist for these groups. University of Michigan, Ann Arbor, MI, USA 40 J. R. Ehrlich et al.

1 Introduction 2 Methods of the Literature Review

Low vision is defined as a chronic, uncorrectable visual A search of the PubMed/MEDLINE database was per- impairment that impacts daily life [1]. Unlike individuals formed in May 2016. The Medical Subject Heading with blindness, those with low vision have remaining sight (MeSH) term ‘randomized controlled trial’ was searched in that can be used for planning or executing tasks [2]. The combination with the following terms or groups of terms: number of adults in the US who are blind or have low (1) vision, low; (2) blindness; (3) vision, ocular and reha- vision is expected to reach 5.5 million by 2020 [3]. Low- bilitation; and (4) vision, ocular and activities of daily vision rehabilitation (LVR) aims to improve patients’ living (ADLs). There were no restrictions on publication functional abilities and may involve the use of assistive dates and only English-language articles were included. devices, occupational therapy and/or education. Notably, in We identified RCTs of LVR that employed patient-re- addition to improving functioning, LVR has also been ported or directly observed task performance as a study shown to improve health-related quality of life (QOL) and outcome measure. References were first selected from psychosocial well-being [4]. search results based on a review of search titles. Abstracts Standard measures of visual function, such as visual were then reviewed and relevant articles were reviewed in acuity (how well a patient can see the eye chart) and visual full. Studies were included if they had a control group; fields (the extent of a patient’s peripheral vision), remain randomly assigned participants to two or more study arms; the mainstay of eye care professionals; however, patients, sought to determine the effectiveness of a low-vision funding agencies, and the vision research community have device or rehabilitation strategy; and had as a primary and/ begun to demand the inclusion of patient-centered outcome or secondary outcome a survey-based patient-reported or (PCO) measures in research, including as outcomes of performance-based functional assessment. RCT study clinical trials and comparative effectiveness studies [5]. In protocols that met the inclusion criteria were reviewed fact, Healthy People 2020, the US population health pri- even if their results were not yet available. Additionally, a orities, includes promoting the health and well-being of prior systematic review of research in the field of LVR people with disabilities and improving health-related QOL published in 2012 [4] was consulted, and RCTs identified among its objectives [6]. Along with the establishment of by this publication were also considered for inclusion. the Patient-Centered Outcomes Research Institute in 2010 Studies were excluded if a full description of their outcome under the Affordable Care Act [5], this signals increasing measure(s) was not available in the scientific literature. recognition of the importance of understanding how Studies employing QOL instruments were also excluded; patients are personally affected by illness and disability. In however, a QOL instrument was included if it contained low-vision research, this is particularly relevant. Since the questions that explicitly probed functioning (e.g. National functional needs and abilities of individual patients dictate Eye Institute Visual Functioning Questionnaire-25 [NEI the goals of rehabilitation, it is important to have outcomes VFQ] [9]). We extracted information pertaining to each for LVR interventions that capture changes in function. outcome measure’s domain(s) and the RCT(s) in which it To date, there is little evidence on the effectiveness of was utilized. When available, we reviewed the validation different LVR strategies for populations with low vision studies of PCOs in order to determine their psychometric [7]. This was underscored by a systematic review of the properties and responsiveness to LVR. literature in 2012 that identified only seven randomized controlled trials (RCTs) in the field of LVR [4]. Rigorously evaluating the effectiveness of rehabilitation strategies 3 Results depends, in part, on the selection of appropriate outcome measures from among the many instruments available to Overall, 470 unique articles matched our search criteria, of researchers [8]. Accordingly, we sought to identify all which 13 met our inclusion criteria. An additional two patient-reported and performance-based functional assess- studies meeting the inclusion criteria were identified by ments that have been employed as outcome measures in review of a publication from 2012 that summarized the RCTs of LVR, including those published since the most literature at that time [4]. A total of 15 RCTs of LVR were recent review of the literature [4]. We have identified the identified that together employed nine unique patient-re- advantages and disadvantages of these functional outcome ported, five unique performance-based, and one hybrid measures in order to suggest future directions for instru- (combined patient-reported and performance-based) func- ment selection and development, which may enable the tional assessment tools. Table 1 summarizes these outcome generation of high-quality evidence and, ultimately, the measures, the domains tested by each instrument, and improved functioning of individuals with low vision. whether the instrument had undergone validation in Patient-Centered Outcomes in Low-Vision Rehabilitation Trials 41

Table 1 Functional outcome measures in randomized controlled trials of low-vision rehabilitation Outcome measure RCT(s) Domain(s) Validated in low vision with Rasch/ IRT modeling

Patient-reported outcome measures Activity Inventory [19] Dunbar et al. [27] Reading; mobility; visual motor; visual Yes Pearce et al. [26] information Rovner at al. [25] Canadian Occupational Atasavun and Du¨ger [72] Self-care; productivity; leisure No Performance Measure [13] Functional Assessment McCabe et al. [28] Self-care; home care; travel; writing; Yes Questionnaire [20] reading; recreation; use of various tools or machines Groningen Activity Ballemans et al. [73] ADLs; instrumental ADLs; mobility No Restriction Scale [14] Impact of Vision Christy et al. [31] Reading and accessing information; mobility Yes Impairment and independence; emotional well-being Questionnaire [21] Katz’ Index of ADL Eklund et al. [74] Cleaning; shopping; transportation; cooking; No [15] personal care Low Vision Quality of Burggraaff et al. [35] Distance vision, mobility and lighting; Yes Life Questionnaire [22] adjustment; reading and fine work; ADLs NEI Visual Functioning Brody et al. [38] General health; general vision; near vision; Yes Questionaire-25 [9] Rovner at al. [25] distance vision; driving; peripheral vision; color vision; ocular pain; role limitations; Scanlan and Cuddeford [39] dependency; social function; mental health Smith et al. [41] Veterans Affairs Low LOVIT I [7] Reading; mobility; visual information Yes Vision Visual LOVIT II [44] processing; visual motor skills Functioning Questionnaire [23] Performance-based outcome measures Activity Card Sort [16] Girdler et al. [75] Activity participation levels Functional Vision McCabe et al. [28] Reading; object identification Performance Test [48] Minnesota Low Vision LOVIT II [44] Reading acuity; reading speed; critical print size Reading Test [45] Pepper Visual Skills for Scanlan and Cuddeford [39] Reading speed; reading accuracy Reading Test [46] Radner Reading Charts Burggraaff et al. [53] Reading acuity; reading speed; critical print size [47] Hybrid outcome measures Melbourne Low-Vision Smith et al. [41] Basic self-care ADLs (patient-reported); Yes ADL Index [54] complex instrumental ADLs (performance-based) ADL activities of daily living, IRT item-response theory, LOVIT Low Vision Intervention Trial, NEI National Eye Institute, RCTs randomized controlled trials patients with low vision using item-response theory (IRT) (PRO) measures in low vision ask patients to assess their or Rasch modeling (a form of IRT), the gold-standard capacity to do specific tasks (e.g. how well are you able to methods for validating a scaled outcome measure [10]. read?). In contrast, performance measures rely on direct observation of patients attempting to complete tasks (e.g. 3.1 Patient-Centered Outcome (PCO) Measures how many words per minute can a patient read correctly?) of Functioning and are often scored with an emphasis on the time required to complete a task and/or the number of errors made. Both Two main types of PCOs—patient-reported [8] and per- types of PCOs may assess ADLs such as self-care and formance-based [11] measures—have been used to assess mobility, or more demanding instrumental ADLs (IADLs) functioning in RCTs of LVR. Patient-reported outcome such as balancing a check book [11]. 42 J. R. Ehrlich et al.

It is important to distinguish between surveys of noted when a patient is more easily able to perform tasks vision-related or health-related QOL and patient-reported and goals that he or she identifies as important. performance/functioning. Thefocusofthisreviewwas Rovner et al. derived a measure termed ‘targeted vision on instruments that assess functioning, not health-related function’ (TVF) from the AI for use in an RCT to compare QOL. Although improved functioning may result in the effectiveness of problem-solving therapy and support- greater health-related QOL, thisisacomplexmetricthat ive therapy for patients with age-related macular degen- also incorporates other constructssuchasemotionaland eration (AMD) [25]. They found that TVF scores improved social well-being [12]. In LVR, observed and reported for both study arms but that neither intervention was function are optimal outcomes since they are subject to superior. In another RCT, Pearce et al. employed the AI fewer confounding and modifying inputs than health- [26] to compare task difficulty for patients receiving a low- related QOL, and they are the explicit targets of vision device during a single visit with an optometrist rehabilitation. compared with patients receiving additional device train- A variety of instruments have been used to measure the ing. They found no difference in functioning between outcomes of LVR in RCTs [8]; however, many of these, groups, but note that this could be due to the simple nature such as general ADL assessments [13–16] and vision-re- of the devices provided in their study. Additionally, Dun- lated QOL instruments [9], were not developed for this bar et al. published a study protocol in which they used the purpose. Additionally, many past studies have reported AI to test the effectiveness of standard LVR compared with summaries of Likert scores across items, an approach with delayed intervention for individuals with diabetic eye dis- poor psychometric validity [8, 10]. In fact, relatively few ease [27]. PCOs have been developed and rigorously validated to assess the functional outcomes of LVR. We focused our 3.2.2 The Functional Assessment Questionnaire detailed review on instruments that meet these criteria since these are more likely to be directly relevant to the The Functional Assessment Questionnaire (FAQ) [20] was outcomes of LVR [17, 18]. developed through consultation with LVR experts who identified key functional domains. They then devised a list 3.2 Patient-Reported Functional Outcome of activities to populate each domain, and Rasch analysis Measures was performed on expected difficulty ratings assigned by LVR experts to each task. Misfit and redundant items were We identified nine unique PROs that have been used as eliminated and remaining items were administered to a outcomes in RCTs of LVR. Three of these are general ADL group of patients. Following a second round of Rasch assessments [13–15] that have not been validated for analysis, the final questionnaire contained 74 items. How- patients with low vision, while the remaining six instru- ever, individuals with low vision were not consulted in the ments consist of questionnaires designed to assess general instrument development process and this could impact the vision-related functioning [9] or functioning in patients relevance of the FAQ to patients’ LVR goals. with low vision [19–23]. McCabe et al. employed the FAQ in an RCT to test whether there was a benefit to incorporating families in 3.2.1 The Activity Inventory low-vision interventions [28]. Although the investigators found that FAQ scores improved for both groups after The Activity Inventory (AI) [19] takes an innovative LVR, they concluded that their sample size was not large approach to surveying patient functioning. To develop the enough to show a difference between study arms. AI, a chart review was performed to determine the functional limitations and rehabilitation aims of patients pre- 3.2.3 Impact of Vision Impairment senting for LVR. Investigators identified over 450 tasks (e.g. writing a check) that they categorized under 50 goals The Impact of Vision Impairment (IVI) questionnaire [21] (e.g. managing finances), and three common objectives was developed through a combination of focus groups and (e.g. daily living). The AI is administered adaptively by a review of existing measures for items that targeted computer-assisted interview [24]. Since asking patients restriction of ADLs. Lamoureux et al. used Rasch analysis about performance of more than 450 tasks would be to refine and validate the original 32-item questionnaire, onerous, if a patient rates a goal ‘not difficult’ or not which resulted in the final 28-item IVI [29]. The same something that he or she wants to do, they do not receive group of researchers found a modest but significant questions related to that goal and its corresponding tasks. improvement in patient-reported functioning following An advantage of the AI is that it provides an individualized rehabilitation in a heterogeneous group of patients with low assessment wherein an improvement in functioning is vision [30]. They attribute the smaller than expected effect Patient-Centered Outcomes in Low-Vision Rehabilitation Trials 43 size to the uncontrolled design of their study and variation the rehabilitation goals of patients with low vision [17]. in the low-vision services and devices that subjects utilized. This finding is not surprising since the NEI VFQ was Christy et al. published a protocol for an RCT comparing designed to be a general vision-related QOL assessment various combinations of center- and home-based LVR and not a functional assessment of LVR goals. Notwith- using the IVI as an outcome measure [31]; results of this standing some concerns about the use of the NEI VFQ as trial have not yet been reported. The advantages and an outcome measure in RCTs of LVR, it has been more drawbacks of the IVI as an RCT outcome are not yet commonly employed in this capacity [25, 38–41] than apparent; however, this instrument and the related IVI- other PCOs identified in this study. Very Low Vision questionnaire [32] were developed with Brody et al. evaluated the efficacy of a health education input from multiple members of the care team and have program to improve problem solving skills for patients been rigorously validated. They represent promising out- with AMD and found a significantly greater improvement come measures for future RCTs in the field. in NEI VFQ scores in the intervention group compared with controls [38]. However, data were not Rasch analyzed 3.2.4 Low Vision Quality-of-Life Questionnaire and the study did not report whether the VFQ domains that contributed to the findings related more closely to vision- Wolffsohn and Cochrane created the Low Vision Quality- related QOL or patient functioning. In another RCT, of-Life Questionnaire (LVQOL) [22]. Questions on this Rovner et al. compared several educational interventions to survey assess task performance and were selected based on improve functioning in patients with AMD [25]. They did interviews with a multidisciplinary team of LVR profes- not detect a change in total Rasch-modified NEI VFQ sionals. Classical test theory was used to select items for scores in either arm of the trial (although the vision-related inclusion in the final measure. The LVQOL has since been QOL domains improved), and the authors suggest that this validated using Rasch analysis [33], and a multi-level IRT instrument may be insensitive to interventions meant to model was used to illustrate its longitudinal sensitivity to address individually valued goals. Scanlan and Cuddeford change with visual deterioration [34]. However, like the also employed the NEI VFQ in their trial comparing basic FAQ, the LVQOL did not utilize the perspectives of indi- rehabilitation and a prolonged educational intervention for viduals with low vision in its development. patients with AMD [39]. They found a greater improve- In an RCT, Burggraaff et al. compared LVQOL scores ment for the prolonged education arm of the study com- for a heterogeneous group of patients who were random- pared with controls, although data were not Rasch ized to receive a closed-circuit television (CCTV) with or analyzed. Finally, Smith et al. employed the NEI VFQ as without hands-on outpatient training [35]. They found that an outcome measure in an RCT that tested the effectiveness both study arms reported less difficulty with reading and of prism glasses to relocate the retinal image for patients fine work after the intervention, but they did not find a with AMD [41]. This trial was unique in LVR in that it was difference between the two groups. placebo controlled, with one arm receiving spectacles matched in weight and thickness but containing no prism. 3.2.5 National Eye Institute Visual Functioning The study did not show an improvement on any of its Questionnaire outcome measures, including the NEI VFQ, for patients receiving prism glasses compared with conventional The NEI VFQ was initially developed as a 51-item ques- spectacles. The authors cite prior studies that advocated the tionnaire [36] but was later shortened to the 25-item ver- use of prisms in this patient population, but assert that their sion [9] that has been frequently employed in functional rigorous study design demonstrates that prism spectacles assessments and studies of vision-related QOL. The NEI are not effective in improving clinical outcomes or PCOs VFQ was developed through a series of focus groups with for patients with low vision due to AMD. individuals with a wide spectrum of eye conditions [36]. Although it was not initially validated with Rasch or IRT 3.2.6 Veterans Affairs Low-Vision Visual Functioning modeling, Marella et al. subsequently used Rasch modeling Questionnaire to assess its psychometric properties for a low-vision population [37] and suggested scoring the instrument on The Veterans Affairs Low-Vision Visual Functioning separate visual functioning and socioemotional scales to Questionnaire-48 (LV VFQ) [42] was designed to measure improve its validity. Stelmack et al. used the NEI VFQ plus outcomes of low-vision services. Stelmack et al. derived supplement (34 items total) to measure the longitudinal the instrument’s 48 items from three sources: question- effect of LVR on visual ability. They found that only seven naires that the authors had previously developed to evalu- items were sensitive to change after LVR, which led them ate navigation, resolution, peripheral detection finding, and to question whether this instrument adequately represents general function; interviews with rehabilitation specialists 44 J. R. Ehrlich et al. about the tasks they commonly taught; and closed-ended an individual’s reading speed and accuracy. Use of this test interviews that asked patients if they could perform tasks has been advocated in the design of LVR training programs independently or with a low-vision device. The instrument [51]. The Rader Charts and MNread both use short simple has been appropriately validated with Rasch modeling [23] sentences (third-grade level) in varying print sizes [50]to and was shown to be sensitive to the effect of LVR [43]. measure reading acuity, speed and critical print size; An advantage to this instrument is the large number of however, the third-grade reading level of the Radner and well-described evaluations of its psychometric properties. MNread tests may be too simple for many individuals who Drawbacks include the use of closed-ended patient inter- would like to read at a higher level and this may induce a views for instrument development and its questionable ceiling effect. Additionally, each of these tests consists of relevance to patients with causes of visual impairment single words or sentences that may not accurately represent other than macular disease [23]. the demands of everyday reading or the rehabilitation goals The LV VFQ served as the primary outcome in the Low of some patients. More recently, Calabre`se et al. developed Vision Intervention Trial (LOVIT) [7], which showed a The Reading Accessibility Index, which accounts for mean significant improvement in functioning for patients with reading speed across various print sizes and normalizes this macular disease undergoing low-vision therapy compared relative to the average reading speed of normally sighted with controls. In their systematic review of the literature, adults [52]; this metric however has not yet been used in Binns et al. concluded that the LOVIT showed the least RCTs. potential for bias out of all RCTs they identified in the field In an RCT, Scanlan and Cuddeford [39] used the Pepper [4]. More recently, LOVIT II [44] completed enrollment Test and found that LVR combined with a prolonged and will report on the impact of competing LVR strategies educational intervention was beneficial compared with using the LV VFQ as its primary outcome. standard rehabilitation. In another trial, Burggraaff et al. [53] employed Radner Charts (along with the LVQOL) to 3.3 Performance-Based Functional Outcome compare the effect of CCTV with and without hands-on Measures outpatient training. As with the LVQOL, no difference between groups was detected with this instrument. Finally, We identified three measures of reading ability [45–47] and Stelmack et al. utilized the MNread as an outcome, along one battery of performance tests [48] that have been with the LV VFQ, in the LOVIT II trial. employed as performance-based outcome measures in RCTs of LVR. An additional outcome measure, the 3.3.2 Functional Vision Performance Test Activity Card Sort [16], is most commonly used in occupational therapy to assess patient participation levels in The Functional Vision Performance Test (FVPT) [48] various activities but has not been fully validated in indi- measures performance on four standardized tasks, includ- viduals with low vision. ing spot reading, short-term text reading, identifying cur- rency, and clock reading. Scores for each item are binary 3.3.1 Measures of Reading Ability (correct/incorrect) rather than using an interval scale based on standard descriptive criteria or a linear scale that com- Since difficulty reading tends to be the most common bines speed and accuracy. A drawback of this instrument is complaint of patients with low vision [49], it is not sur- that binary scoring may result in reduced measurement prising that trials have used reading speed and/or accuracy precision and may create floor or ceiling effects that result as an outcome measure. Nonetheless, it can be challenging in an underestimation of effect size. Additionally, interval to measure performance of tasks such as reading since scoring with standardized descriptive criteria could there is often a trade-off between speed and accuracy. improve measurement validity and precision by matching Commonly tested reading parameters include the smallest the abilities of subjects to item difficulties through Rasch or print size that can be read (reading acuity); the number of IRT modeling. McCabe et al. employed the FVPT in their words read correctly per minute (reading speed); and the aforementioned RCT, which they state was underpowered smallest print size that can be read at maximum reading to show a benefit to including families in LVR [28]. speed (critical print size) [50]. Several tests of reading performance have been 3.4 Hybrid Functional Outcome Measures employed as outcomes in RCTs, including the Pepper Visual Skills for Reading Test [46], Radner Reading Charts Little work has been undertaken to determine the value of [47], and the Minnesota Low-Vision Reading Test combining PROs and performance-based outcome mea- (MNread) [45]. The Pepper Test contains 13 lines of print, sures. One exception is the Melbourne Low Vision ADL increasing from single letters to compound words, and tests Index (MLVAI), which contains nine survey questions to Patient-Centered Outcomes in Low-Vision Rehabilitation Trials 45 assess basic self-care ADLs, along with direct observation and patient-reported functioning, as well as the advantages of 16 complex IADL tasks [54]. Items for MLVAI were and disadvantages of each of these (Table 2). chosen based on the frequency with which they appeared in There is suggestion that observed and patient-reported existing outcome measures and their relevance to visual functioning do not always agree and this was shown in the impairment and LVR. The performance-based items are Salisbury Eye Evaluation (SEE) [57]. Patients in SEE scored by observers from 0 to 4 using standardized answered questions about difficulty executing various tasks descriptive criteria. To validate the MLVAI, researchers and completed a performance assessment that included used Rasch modeling in a population of patients with mobility, facial recognition, and reading. The study showed predominantly central vision loss. They found that clinical that 10 % of subjects did not read at a rate compatible with measures of vision were more strongly correlated with sustained reading but reported minimal or no difficulty observed task performance than with the self-reported reading. In another investigation, Szlyk et al. found items, and that MLVAI scores improved significantly in agreement between patient-reported and observed func- patients with macular degeneration undergoing LVR [55]. tioning for most tasks among patients with retinitis pig- In a subsequent study, the authors developed a modified mentosa [58]; however, they noted that patients tended to version of the MLVAI in which items were weighted based overestimate their capacity to perform peripheral detection on the importance of each task to the individual being tasks and to underestimate their mobility. Further evidence tested [56]. In the previously cited RCT, Smith et al. of the discrepancy between observed and reported function employed the MLVAI as one of several outcome measures comes from outside ophthalmology, where researchers to test the effectiveness of prism glasses that relocate the found that performance measures were better predictors of retinal image for patients with AMD [41]; they did not find mortality than proxy- or self-reported function among any clinical or functional benefit to this intervention. geriatric patients [59]. As mentioned, performance measures carried out in a controlled setting may not reflect tasks performed under everyday conditions [60]. However, 4 Discussion in SEE, West et al. found that performance of visually intensive tasks in the clinic was highly correlated with The large number of outcome measures that has been uti- performance in the home [61]. Another possibility is that lized in studies of LVR has been an impediment to discrepancies between patient-reported and performance understanding and comparing the effectiveness of rehabil- measures may be a reflection of the importance that an itation strategies and devices. For example, both Rovner el individual attributes to a given task. Notwithstanding, the al. [25] and Brody et al. [38] performed interventions to results of these studies suggest the possibility of differen- test the effectiveness of different problem-solving strate- tial measurement error and/or different latent constructs gies for patients with AMD; however, since each study underlying performance-based and patient-reported per- employed different outcome measures, their results cannot formance. Future work should be undertaken to establish be compared and no conclusion can be made about the performance testing standards that mimic conditions found relative effectiveness of the interventions. To promote outside of the laboratory or clinic and to understand better comparability of rehabilitation strategies and to strengthen the factors that mediate the relationship between patient- research in the field of low vision, it will be important to reported and directly observed performance. adopt agreed-upon outcome measures that are valid, reliable, precise and sensitive to the effect of LVR. 4.2 Measurement Issues in PCOs

4.1 Survey and Performance Measures Compared In order to assess the functional abilities of patients, measures need to account for both the difficulty of tasks Patients undergo LVR in order to improve their capacity to and the abilities of subjects. Functional capacity may be perform specific tasks. Thus, outcome measures in RCTs rated on an ordinal Likert scale with response categories must be able to assess how well a patient can perform a matched to numerical values, for example ranging from task at the start and completion of a trial in order to ‘impossible’ to ‘not difficult’. To score these instruments, a compare study arms and measure efficacy. Direct obser- patient’s responses can be summed across items. This vation provides objective information about an individual’s approach assumes that the difference between any two capacity to perform a given task; however, PROs may response categories is equal, although this is rarely the better capture patients’ everyday experiences compared case. Additionally, Likert scoring does not match the dif- with performance in a controlled setting. Accordingly, to ficulty of items to patients’ abilities and this can result in an select the most appropriate set of outcome measures, it is underestimation of effect size due to floor and ceiling crucial to understand the relationship between observed effects. 46 J. R. Ehrlich et al.

Table 2 Limitations of patient-reported and performance measures in low-vision rehabilitation Limitation Patient-reported performance Observed performance

Questionable face validity 4 Confounded by patient mood 4 Impacted by culture, language, education, cognitive function 44 Hawthorne effect 44 Longer test time 4 Trade-off between speed and accuracy 4 Need for special equipment 4 Impacted by ﬂuctuation in vision 4 Not representative of everyday experiences 4

IRT and Rasch analysis, a form of IRT, seek to address walking or reading speed, nor do all desire improvement of these issues by modeling the relationship between a latent these tasks. These kinds of personal and cultural differ- trait (e.g. a patient’s functional visual ability) and the items ences should be accounted for; however, personalization of being used to measure that trait. The Rasch model has been outcome measures introduces operational and statistical widely employed in vision research to estimate an interval challenges since outcomes must also be standardized and scale for a population and a set of items, to detect misfit of comparable between patients and studies. One method of items, and to evaluate the unidimensionality of a measure, a addressing this is with computer-adaptive testing (CAT), key assumption when calculating composite scores. While a which has been widely used in other areas of medicine. more detailed discussion of measurement theory and psy- However, Massof has noted that CAT can produce inac- chometrics is beyond the scope of this article, Massof curacies and inefficiencies in assessing rehabilitation out- provided an extensive review of these topics as they relate comes [62]. Instruments can also be made adaptive, such as to vision research [10]. Importantly, there is growing con- the AI [24] or the MLVAI [56], by weighting goals or sensus that item response models should be employed to items based on their importance to the patient. Addition- evaluate the validity of scaled outcome measures. ally, task difficulty could be varied in order to determine An additional methodological concern is how to best the threshold beyond which performance is impaired for a combine patient-reported and performance-based out- given individual [63]. Nonetheless, since some patients comes, an approach that is appealing since it could draw on will select ‘harder’ or ‘easier’ rehabilitation goals, this may the advantages of each type of instrument. However, cer- impact their scores. Consideration should be given to how tain measurement issues should be kept in mind that may these theoretical issues can be addressed, as doing so could require innovative solutions in order to take full advantage help to bring outcome measure personalization and preci- of this complex approach. First, patient-reported and per- sion medicine to the field of LVR. formance measures are likely to have different sources of variance and this may result in distortion of measurements. 4.3 Relevance to Patients Additionally, observations for different tasks may be in different units and this requires the use of complex models Outcome measures should include items that are designed with decreased measurement precision. One approach to to match the impairments and goals of their target patient this limitation is to score tasks using standard descriptive population, as doing so will improve their validity [64] and criteria, as the MLVAI does; however, this approach can their ability to detect the effect of an intervention [18]. result in decreased measurement reliability since it depends Currently, the relationship between the rehabilitation pri- on the assessments of trained observers. Future method- orities and perceived functional limitations of patients, ological work may seek to address some of these theoret- their caretakers, and clinicians is not well understood. ical issues. However, understanding the perspectives of each member Attention should also be directed toward how to best of the care team could result in future outcome measures individualize outcome measures to match patients’ unique that are more relevant to patients, their rehabilitation goals abilities and rehabilitation goals. To achieve this, it is and the delivery of LVR. necessary to understand the ease or difficulty of performing Additionally, as many existing instruments were devel- certain tasks for an individual patient, as well as the level oped and/or validated predominantly among adult patients of importance that that individual places on performing the with central vision loss [19, 21, 23, 48, 54], they may not task. All individuals do not have the same potential be relevant to children or to individuals with peripheral Patient-Centered Outcomes in Low-Vision Rehabilitation Trials 47 vision loss or physical disabilities. In fact, there is evidence 5 Conclusions that some well-designed and validated instruments may not be suited to patients with low vision resulting from There have been few RCTs in the field of LVR. Conse- peripheral vision loss. In one study, Noe et al. tested the quently, the effectiveness of many rehabilitation strategies association between peripheral vision loss due to glaucoma for different groups of patients with low vision remains and IVI scores, and only found a positive association with unknown. Past RCTs have employed an array of different the instrument’s mobility domain [65]. Additionally, the patient-reported and performance-based instruments as trial LV VFQ investigators noted that some items they expected outcomes. A number of these have been shown to be to be sensitive to visual field loss were ‘misfit’ and had to psychometrically valid and sensitive to the effect of LVR be removed to improve the validity of the final question- [19–23, 45–47, 54]. Future RCTs in LVR should look to naire [23]. The researchers suggested that this may have these instruments as potential outcome measures while occurred since their study population consisted of only a considering the baseline abilities and goals of participants small number of patients with peripheral vision loss, and and the intervention(s) being studied. Additionally, exam- these patients are likely to experience low vision differ- ining the psychometric properties of an instrument and its ently than patients with central vision loss. For example, development process can help to ensure that a chosen there is evidence that individuals with peripheral vision instrument is relevant and valid for a trial’s target popu- loss are more likely to experience impaired mobility [66]. lation. Adequate outcome measures may still not exist for Future efforts should focus on developing and validating some rehabilitation strategies or low-vision patient popu- relevant multi-task outcome measures for patients with lations. In such cases, instrument development should be severe peripheral vision loss since comparatively little undertaken with attention to the qualitative insights of work [67] has been carried out in this area. affected individuals. Additionally, investigators may con- sider strategies to make outcomes adaptive to the patients’ 4.4 Bias and Confounding varied rehabilitation goals. Future work should also focus on better understanding the relationships between patient- It is essential to recognize the unique set of biases and con- reported and performance-based assessments as this will founders that impact patient-reported and performance- provide important information for both clinical practice based outcomes. When used to measure effectiveness of an and research in LVR. Evidence-based progress in the field intervention, surveys can be susceptible to social desirability of LVR depends on the design of rigorous RCTs and their bias [68], wherein patients may report functional improve- adoption of reliable, valid and highly relevant PCO ment in order to please their rehabilitation team. This bias measures. can result in overestimation of effect size. Additionally, mood can impact survey responses. In the Collaborative Author Contributions Each author meets the criteria for authorship laid out by the International Committee of Medical Journal Editors. Initial Glaucoma Treatment Study, subjects who were Each author has given final approval for the manuscript to be sub- depressed reported that they had worse visual function, even mitted for consideration for publication. All authors agree to be though their measured visual acuity and visual fields did not accountable for all aspects of the work and Dr. Ehrlich will act as the demonstrate worsening [69]. This phenomenon, termed overall guarantor. The individual contributions of each author are listed: Joshua Ehrlich: Conception and design of the study, writing of operational confounding, could alter trial outcomes in an the manuscript. George Spaeth: Conception and design of the study, unpredictable manner since mood may vary from test to test. critical revision of the manuscript. Noelle Carlozzi: Critical revision Traits other than visual impairment may also affect perfor- of the manuscript. Paul Lee: Conception and design of the study, mance outcomes but often in a more predictable manner. For critical revision of the manuscript. This submission has not been previously published elsewhere and is not simultaneously being example, a patient with low vision and Parkinson disease is considered for any other publication. more likely to have mobility problems than a similar patient without Parkinson disease. However, prior work has also Compliance with Ethical Standards shown that language, cognitive ability, education, and culture may influence the results of both survey and perfor- Grants This work was supported by the Heed Ophthalmic Founda- tion through an unrestricted Grant to Joshua Ehrlich (no Grant mance measures [70]. Finally, the clinical setting may bias a Number). patient to try harder or longer at a task than they would at home, and the Hawthorne effect may cause individuals to Conflict of interest Joshua Ehrlich, George Spaeth, Noelle Carlozzi, modify their responses or behavior in reaction to being and Paul Lee have no conflicts of interest that impacted or are likely to be perceived as impacting their contribution to this work. Paul Lee observed [71]; both of these phenomena could result in better is a consultant to the Centers for Disease Control and Prevention. All performance in the clinic compared with in the home. money goes to his institution. 48 J. R. Ehrlich et al.

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