Development of a battery of functional tests for low vision

Performance on clinical outcomes, activities of daily living and user experience on head-mounted displays for people with vision impairment

PURPOSE

To compare the objective performance, acceptance and usability of head-mounted displays (HMDs) to provide evidence-based data that could be used to increase the efficiency of device referrals based upon a person's vision loss and functional needs.

METHODS

A cross-sectional, counterbalanced, individually controlled crossover study was performed on 15 adults with various eye conditions. Performance was measured when using four HMDs: eSight4, Eyedaptic EYE3, Eyedaptic EYE4 and IrisVision Inspire. Performance on clinical visual acuity tests and contrast were assessed, as well as vision-related activities of daily living (ADL) which were divided into three categories: Reading, Searching & Identifying and Eye-hand Coordination. User-experience was also assessed. Logistic regression analyses, Friedman one-way repeated measure analyses of variance by ranks and multivariate permutation testing were used for analysis.

RESULTS

There was a significant improvement in visual acuity when using all devices. For contrast tasks, only the eSight4 and Eyedaptic EYE3 improved performance relative to baseline. For most Reading and Searching & Identifying tasks, the odds of being able to perform the tasks were significantly higher while using the devices. However, the actual performance with most devices (e.g., number of words read or reading speed) did not improve significantly over baseline for most tasks. For the Eye-hand Coordination tasks, participants performed equivalent to or significantly poorer than baseline when using the devices. No demographic or clinical predictors of outcomes were identified. Participants expressed dissatisfaction with the devices' effectiveness, acceptability and usability.

CONCLUSIONS

While performance on clinical tests was better when using the devices, performance on most real-world ADLs was equal to or worse than baseline. No single device improved performance on all tasks, and performance on any one task was not improved with all the devices. The overall dissatisfaction with the devices paralleled the lack of objective improvement in the performance of real-world tasks.

Gaze and behavioural metrics in the refractive correction of presbyopia

PURPOSE

To investigate gaze and behavioural metrics at different viewing distances with multifocal contact lenses (MFCLs), single vision contact lenses (SVCLs) and progressive addition lenses (PALs).

METHODS

Fifteen presbyopic contact lens wearers participated over five separate study visits. At each visit, participants were randomly assigned to wear one of five refractive corrections: habitual PAL spectacles, delefilcon A (Alcon Inc.) MFCLs and three separate pairs of delefilcon A single vision lenses worn as distance, intermediate and near corrections. Participants wore a Pupil Core headset to record eye and head movements while performing three visual tasks: reading, visual search and scene observation. Data were investigated using linear regression and post-hoc testing. Parameters of interest included gaze (fixation duration, head movement) and behavioural (reading speed, reading accuracy, visual search time) metrics.

RESULTS

Reading speed in SVCLs was significantly faster than in MFCLs and PAL spectacles (F = 16.3, p < 0.0001). Refractive correction worn did not influence visual search times (F = 0.16, p = 0.85). Fixation duration was significantly affected by the type of visual task (F = 60.2, p < 0.001), and an interaction effect was observed between viewing distance and refractive correction (F = 4.3, p = 0.002). There was significantly more horizontal and vertical head movement (F = 3.2, p = 0.01 and F = 3.3, p = 0.01, respectively) during visual search tasks when wearing PAL spectacles compared to SVCLs or MFCLs.

CONCLUSION

This work showed that the type of refractive correction affects behavioural metrics such as reading speed and gaze behaviour by affecting horizontal and vertical head movements. The findings of this study suggest that under certain conditions, wearers of MFCLs make fewer head movements compared to PAL spectacles. Gaze behaviour metrics offer a new approach to compare and understand contact lens and spectacle performance, with potential applications including peripheral optical designs for myopia management.

Effect of low luminance on face recognition in adults with central and peripheral vision loss

PURPOSE

To investigate the effect of low luminance on face recognition, specifically facial identity discrimination (FID) and facial expression recognition (FER), in adults with central vision loss (CVL) and peripheral vision loss (PVL) and to explore the association between clinical vision measures and low luminance FID and FER.

METHODS

Participants included 33 adults with CVL, 17 with PVL and 20 controls. FID and FER were assessed under photopic and low luminance conditions. For the FID task, 12 sets of three faces with neutral expressions were presented and participants asked to indicate the odd-face-out. For FER, 12 single faces were presented and participants asked to name the expression (neutral, happy or angry). Photopic and low luminance visual acuity (VA) and contrast sensitivity (CS) were recorded for all participants and for the PVL group, Humphrey Field Analyzer (HFA) 24-2 mean deviation (MD).

RESULTS

FID accuracy in CVL, and to a lesser extent PVL, was reduced under low compared with photopic luminance (mean reduction 20% and 8% respectively; p < 0.001). FER accuracy was reduced only in CVL (mean reduction 25%; p < 0.001). For both CVL and PVL, low luminance and photopic VA and CS were moderately to strongly correlated with low luminance FID (ρ = 0.61-0.77, p < 0.05). For PVL, better eye HFA 24-2 MD was moderately correlated with low luminance FID (ρ = 0.54, p = 0.02). Results were similar for low luminance FER. Together, photopic VA and CS explained 75% of the variance in low luminance FID, and photopic VA explained 61% of the variance in low luminance FER. Low luminance vision measures explained little additional variance.

CONCLUSION

Low luminance significantly reduced face recognition, particularly for adults with CVL. Worse VA and CS were associated with reduced face recognition. Clinically, photopic VA is a good predictor of face recognition under low luminance conditions.

Differences between high and low performers in face recognition in electrophysiological correlates of face familiarity and distance-to-norm

Valentine's influential norm-based multidimensional face-space model (nMDFS) predicts that perceived distinctiveness of a face increases with its distance to the norm. Occipito-temporal event-related potentials (ERPs) have been recently shown to respond selectively to variations in distance-to-norm (P200) or familiarity (N250, late negativity), respectively (Wuttke & Schweinberger, 2019). Despite growing evidence on interindividual differences in face perception skills at the behavioral level, little research has focused on their electrophysiological correlates. To reveal potential interindividual differences in face spaces, we contrasted high and low performers in face recognition in regards to distance-to-norm (P200) and familiarity (N250). We replicated both the P200 distance-to-norm and the N250 familiarity effect. Importantly, we observed: i) reduced responses in low compared to high performers of face recognition, especially in terms of smaller distance-to-norm effects in the P200, possibly indicating less 'expanded' face spaces in low compared to high performers; ii) increased N250 responses to familiar original faces in high performers, suggesting more robust face identity representations. In summary, these findings suggest the contribution of both early norm-based face coding and robust face representations to individual face recognition skills, and indicate that ERPs can offer a promising route to understand individual differences in face perception and their neurocognitive correlates.

The effects of induced optical blur on visual search performance and training

Visual search is a task often used in the rehabilitation of patients with cortical and non-cortical visual pathologies such as visual field loss. Reduced visual acuity is often comorbid with these disorders, and it remains poorly defined how low visual acuity may affect a patient’s ability to recover visual function through visual search training. The two experiments reported here investigated whether induced blurring of vision (from 6/15 to 6/60) in a neurotypical population differentially affected various types of feature search tasks, whether there is a minimal acceptable level of visual acuity required for normal search performance, and whether these factors affected the degree to which participants could improve with training. From the results, it can be seen that reducing visual acuity did reduce search speed, but only for tasks where the target was defined by shape or size (not colour), and only when acuity was worse than 6/15. Furthermore, searching behaviour was seen to improve with training in all three feature search tasks, irrespective of the degree of blurring that was induced. The improvement also generalised to a non-trained search task, indicating that an enhanced search strategy had been developed. These findings have important implications for the use of visual search as a rehabilitation aid for partial visual loss, indicating that individuals with even severe comorbid blurring should still be able to benefit from such training.

Reliability and validity of the Canadian-French ecological adaptation of the weighted version of the Melbourne low-vision ADL Index

Background: The Mesure de l'impact de la déficience visuelle dans les activités quotidiennes (MIDVAQ) is the Canadian-French adaptation of the Melbourne Low-Vision ADL Index. It measures performance, personal importance and handicap situation in 16 instrumental activities requiring near vision (standardized material, part A) and in 9 self-care and domestic activities (self-report questionnaire, part B). This study aimed at measuring the MIDVAQ reliability and its relationship with measures of visual functions and functional vision.Methods: The MIDVAQ was administered twice to 100 visually impaired participants, at home, with their personal visual and non-visual aid. A second rater was present at T1. Two different versions of part A were used alternately at T1 and T2.Results: The total Handicap scale demonstrates good internal reliability (Cronbach's alpha coefficient = 0.82) and very high inter-rater and test-retest reliability (ICCs = 1.00 and 0.86). Part A alternative versions are highly comparable. Vision function measures are significantly correlated with total Handicap score, for which 48% of the variance is explained by functional vision estimates, age, and education.Conclusions: The MIDVAQ is highly valid and reliable. It can be useful to measure the functional impact of the visual impairment, its progression, and the outcomes of low vision rehabilitation services.Implications for rehabilitationEven if administered at home in an ecological way, this measure of the impact of the visual impairment in daily activities is very reliable.Given its good metric properties, this tool can be confidently used to assess the functional impact of visual impairment, outcomes of the low vision rehabilitation services, etc.This measurement tool provides complementary information to those obtained from clinical measures of visual functions, by reflecting the interaction between the functional abilities with the requirements of the environment.

Occupational performance in the basic and instrumental daily activities of persons with low vision who received rehabilitation services

Introduction

The objective was to describe the occupational performance in basic and instrumental daily activities of persons living in the community who have received comprehensive interdisciplinary low vision rehabilitation services.

Method

The Mesure de l'impact de la déficience visuelle dans les activités quotidiennes (a measure of the impact of visual impairment in daily activities) was administered at home to 102 individuals who participated in a comprehensive low vision rehabilitation program. Performance in 16 near-vision activities was measured with the person's aids and strategies; nine more global tasks were questionnaire-based. Handicap scores were obtained by multiplying performance × importance ratings.

Results

Average performance was satisfactory or very satisfactory for 21/25 items, even if 92% of the participants had a moderate or severe visual impairment. A severe or total handicap was present in at least one activity for 79% of the subjects. The most handicapping activities required visual searches of finely printed information on a complex or visually crowded document, or shopping and mobility.

Conclusion

People with low vision who took part in a comprehensive rehabilitation program generally face no or slight handicap situations in their basic and instrumental daily activities. However, major handicap situations may remain in some important activities.

Visual Search Performance in Patients with Vision Impairment: A Systematic Review

PURPOSE

Patients with visual impairment are constantly facing challenges to achieve an independent and productive life, which depends upon both a good visual discrimination and search capacities. Given that visual search is a critical skill for several daily tasks and could be used as an index of the overall visual function, we investigated the relationship between vision impairment and visual search performance.

METHODS

A comprehensive search was undertaken using electronic PubMed, EMBASE, LILACS, and Cochrane databases from January 1980 to December 2016, applying the following terms: "visual search", "visual search performance", "visual impairment", "visual exploration", "visual field", "hemianopia", "search time", "vision lost", "visual loss", and "low vision". Two hundred seventy six studies from 12,059 electronic database files were selected, and 40 of them were included in this review.

RESULTS

Studies included participants of all ages, both sexes, and the sample sizes ranged from 5 to 199 participants. Visual impairment was associated with worse visual search performance in several ophthalmologic conditions, which were either artificially induced, or related to specific eye and neurological diseases.

CONCLUSIONS

This systematic review details all the described circumstances interfering with visual search tasks, highlights the need for developing technical standards, and outlines patterns for diagnosis and therapy using visual search capabilities.

The Experience of a Randomized Clinical Trial of Closed-Circuit Television versus Eccentric Viewing Training for People with Age-Related Macular Degeneration

Introduction

In addition to optical devices, closed-circuit televisions (CCTVs) and eccentric viewing training are both recognized interventions to improve reading performance in individuals with vision loss secondary to age-related macular degeneration. Both are relatively expensive, however, either in the cost of the device or in the amount of time personnel need to provide training. In this randomized trial, we compared the effectiveness of these two interventions.

Methods

Participants with age-related macular degeneration and visual acuity between 6/48 (20/160) and 6/120 (20/400) first received basic low vision care, including optical devices. At the subsequent baseline visit, they undertook a battery of measures including logMAR visual acuity; reading speed and accuracy for text in 1.3M and 1M fonts; reading information on medicine bottles, utility bills, and food packages; the NEI-VFQ; the Geriatric Depression Scale; and a reading inventory questionnaire. They were then randomized to either obtaining a CCTV for home use or eccentric viewing training over the following six weeks.

Results

Recruitment was more difficult than expected for this population. Of 145 patients referred, 29 met the inclusion-exclusion criteria, 14 were willing to enroll, and 10 completed the trial. For the primary outcome (reading speed for 1.3M print), there was a significant improvement between baseline and outcome for the CCTV group (p = 0.005), but not for the eccentric viewing training group (p = 0.28), and the CCTV group showed significantly greater change (p = 0.04). There was a nonsignificant improvement in reading speed for 1M text and a decrease in the amount of time taken to read utility bill information in the CCTV group. There was a significant improvement in near visual acuity with current glasses with eccentric viewing training. The other measures did not reach statistical significance.

Discussion

Randomized clinical trials for low vision rehabilitation, particularly in the elderly population with vision loss, are challenging, but such trials are important for the allocation of resources. This trial showed early indications of more impact on reading performance from CCTV than eccentric viewing training.

Effect of reduced visual acuity on precision of two-dimensional tracing movements

PURPOSE

We intended to assess consequences of reduced visual acuity for performance in a natural simple motor task (tracing) using objective kinematic performance measures. Specifically, we intended to elucidate the kind of relationship between the task performance and best corrected binocular visual acuity and to determine the threshold of visual acuity when task performance starts to deteriorate.

METHODS

Ninety-five individuals with different best corrected visual acuity participated in the study (age 49±12 years, mean±SD, 27 men and 68 women). The participants manually traced maze-like visual patterns of different spatial complexity presented on the screen of a portable notebook computer using Clinical Kinematic Assessment Tool software. Tracing error was computed as performance measure in each trial with a spatial pattern matching technique - rigid point set registration method.

RESULTS

The segmented linear regression analysis showed that the relation between visual acuity and tracing errors was best described with a regression function having a break point between two data segments. Tracing performance was unaffected by values of visual acuity below 0.2 on logMAR scale, but when logMAR values increased above this critical limit (i.e. when visual acuity is further reduced), tracing errors linearly increased. The rate of the increase of the tracing error correlated with the complexity of visual stimulus shape.

CONCLUSION

Testing of fine motor functions with objective kinematic measures during visuomotor tasks may help differentiating between actual effects of reduced visual acuity on eye-hand coordination in individuals with similar levels of impairment of visual acuity.

Random word recognition chart helps scotoma assessment in low vision

Purpose

To evaluate the use of SKread, a vision test based on random word sequences that prevents the prediction of upcoming words by linguistic criteria and is simple to score in a clinical setting.

Methods

SKread combines the standardized format of the MNread test with sequences of random words and letters like the Pepper Visual Skills for Reading test. A total of 231 subjects (aged 16 to 97 years) participated. We report data from 136 eyes of subjects with a maculopathy and 65 with normal or near-normal vision. Test reliability was investigated on an additional 30 eye-healthy subjects. We tested visual acuity and reading performance for continuous text and random words monocularly. Reading speed and all errors made are reported.

Results

Reading speed was always higher for continuous text than for random word sequences, even in normally sighted subjects for whom the median reading times per paragraph were 2.4 s (MNread) vs. 6.8 s (SKread). In patients with maculopathies, the medians were 4.2 s vs. 12.25 s. These differences were statistically significant. Number and type of errors made depended only negligibly on age and visual acuity. Patients with a dense scotoma right of fixation made more “right errors” by missing letters at the end of words, whereas those with a scotoma left of fixation made more “left errors” by missing letters at the beginning of words. The SKread test showed good test-retest repeatability.

Conclusions

The unpredictability of random word and letter sequences renders reading performance highly dependent on eyesight and less dependent on reading skill and educational level. Recurrent right or left errors can indicate the presence and location of a scotoma without expensive equipment. This knowledge can be used to teach patients about how the scotoma can interfere with their vision.

Characterizing functional complaints in patients seeking outpatient low-vision services in the United States

PURPOSE

To characterize functional complaints of new low-vision rehabilitation patients.

DESIGN

Prospective observational study.

PARTICIPANTS

The Low Vision Rehabilitation Outcomes Study recruited 819 patients between 2008 and 2011 from 28 clinical centers in the United States.

METHODS

New patients referred for low-vision rehabilitation were asked, "What are your chief complaints about your vision?" before their appointment. Full patient statements were transcribed as free text. Two methods assessed whether statements indicated difficulty in each of 13 functional categories: (1) assessment by 2 masked clinicians reading the statement, and (2) a computerized search of the text for specific words or word fragments. Logistic regression models were used to predict the influence of age, gender, and visual acuity on the likelihood of reporting a complaint in each functional category.

MAIN OUTCOME MEASURES

Prevalence and risk factors for patient concerns within various functional categories.

RESULTS

Reading was the most common functional complaint (66.4% of patients). Other functional difficulties expressed by at least 10% of patients included driving (27.8%), using visual assistive equipment (17.5%), mobility (16.3%), performing in-home activities (15.1%), lighting and glare (11.7%), and facial recognition and social interactions (10.3%). Good agreement was noted between the masked clinician graders and the computerized algorithm for categorization of functional complaints (median κ of 0.84 across the 13 categories). Multivariate logistic regression models demonstrated that the likelihood of reading difficulties increased mildly with age (odds ratio, 1.4 per 10-year increment in age; 95% confidence interval, 1.3-1.6), but did not differ with visual acuity (P = 0.09). Additionally, men were more likely to report driving difficulties and difficulties related to lighting, whereas women were more likely to report difficulty with either in-home activities or facial recognition or social interaction (P<0.05 for all). Mobility concerns, defined as walking difficulty and out-of-home activities, showed no relationship to gender, age, or visual acuity.

CONCLUSIONS

Reading was the most commonly reported difficulty, regardless of the patient's diagnosis. Neither visual acuity nor gender were predictive of reading concerns, although, age showed a small effect. Addressing reading rehabilitation should be a cornerstone of low-vision therapy.

A standardized obstacle course for assessment of visual function in ultra low vision and artificial vision

We describe an indoor, portable, standardized course that can be used to evaluate obstacle avoidance in persons who have ultralow vision. Six sighted controls and 36 completely blind but otherwise healthy adult male (n=29) and female (n=13) subjects (age range 19-85 years), were enrolled in one of three studies involving testing of the BrainPort sensory substitution device. Subjects were asked to navigate the course prior to, and after, BrainPort training. They completed a total of 837 course runs in two different locations. Means and standard deviations were calculated across control types, courses, lights, and visits. We used a linear mixed effects model to compare different categories in the PPWS (percent preferred walking speed) and error percent data to show that the course iterations were properly designed. The course is relatively inexpensive, simple to administer, and has been shown to be a feasible way to test mobility function. Data analysis demonstrates that for the outcome of percent error as well as for percentage preferred walking speed, that each of the three courses is different, and that within each level, each of the three iterations are equal. This allows for randomization of the courses during administration.

Clinical Tests of Ultra-Low Vision Used to Evaluate Rudimentary Visual Perceptions Enabled by the BrainPort Vision Device

PURPOSE

We evaluated whether existing ultra-low vision tests are suitable for measuring outcomes using sensory substitution. The BrainPort is a vision assist device coupling a live video feed with an electrotactile tongue display, allowing a user to gain information about their surroundings.

METHODS

We enrolled 30 adult subjects (age range 22-74) divided into two groups. Our blind group included 24 subjects (n = 16 males and n = 8 females, average age 50) with light perception or worse vision. Our control group consisted of six subjects (n = 3 males, n = 3 females, average age 43) with healthy ocular status. All subjects performed 11 computer-based psychophysical tests from three programs: Basic Assessment of Light Motion, Basic Assessment of Grating Acuity, and the Freiburg Vision Test as well as a modified Tangent Screen. Assessments were performed at baseline and again using the BrainPort after 15 hours of training.

RESULTS

Most tests could be used with the BrainPort. Mean success scores increased for all of our tests except contrast sensitivity. Increases were statistically significant for tests of light perception (8.27 ± 3.95 SE), time resolution (61.4% ± 3.14 SE), light localization (44.57% ± 3.58 SE), grating orientation (70.27% ± 4.64 SE), and white Tumbling E on a black background (2.49 logMAR ± 0.39 SE). Motion tests were limited by BrainPort resolution.

CONCLUSIONS

Tactile-based sensory substitution devices are amenable to psychophysical assessments of vision, even though traditional visual pathways are circumvented.

TRANSLATIONAL RELEVANCE

This study is one of many that will need to be undertaken to achieve a common outcomes infrastructure for the field of artificial vision.

The effects of visual degradation on face discrimination

PURPOSE

People with reduced visual acuity (VA) and/or contrast sensitivity have difficulty recognizing faces and facial expressions. We have quantified these difficulties, using a synthetic face discrimination task employing both normal and artificially degraded vision.

METHODS

VA and contrast thresholds were measured using an optimised staircase procedure [Freiburg acuity Test (FrACT)] in 25 young adults (aged 18-24 years) with corrected visual acuity of 0.0 logMAR or better and with four levels of vision degraded with Bangerter occlusion foils. For face discrimination, male face images were synthesised from 37 cardinal points (position of eyes, width of nose, head shape etc) derived from frontal face photographs and manipulated by altering the points as a fraction of the mean head radius. Face discrimination thresholds (% difference) were measured from a simultaneous four-alternative forced choice of 'odd one out' from three identical faces and one that differed. Psychometric functions were measured for four participants with normal and degraded vision. Subsequently, the difference between faces was fixed at twice the discrimination thresholds and the size of the faces manipulated using the FrACT threshold procedure in 25 participants. Data were converted to equivalent face discrimination distances for realistic face dimensions.

RESULTS

With normal vision, face discrimination thresholds ranged from 2.7% to 5.6%; these increased systematically and were more variable with visual degradation. When manipulating face size, face discrimination distance was highly correlated with both acuity and contrast sensitivity (r(2) = 0.77 and 0.80 respectively, p < 0.01). The mean distance with normal vision was 15.3 m (14.5-16.2 ± S.E.M.). With vision degraded to 0.6 logMAR (6/24 Snellen, contrast threshold 15%) the mean face discrimination distance was reduced to 3.9 m (3.7-4.1, ±S.E.M.).

CONCLUSIONS

Poor face discrimination has a profound impact on real-life social communication. Here we report that artificial visual degradation also adversely impacts a synthetic face recognition task. As a rule of thumb, reduction in VA of 0.3 logMAR (halving the decimal VA) reduces the face recognition distance by a factor of 0.6 times. The FrACT-based face discrimination task provides an efficient new tool to quantify and monitor face discrimination ability.

Comparison of scoring approaches for the NEI VFQ-25 in low vision

PURPOSE

The aim of this study was to evaluate different approaches to scoring the National Eye Institute Visual Functioning Questionnaire-25 (NEI VFQ-25) in patients with low vision including scoring by the standard method, by Rasch analysis, and by use of an algorithm created by Massof to approximate Rasch person measure. Subscale validity and use of a 7-item short form instrument proposed by Ryan et al. were also investigated.

METHODS

NEI VFQ-25 data from 50 patients with low vision were analyzed using the standard method of summing Likert-type scores and calculating an overall average, Rasch analysis using Winsteps software, and the Massof algorithm in Excel. Correlations between scores were calculated. Rasch person separation reliability and other indicators were calculated to determine the validity of the subscales and of the 7-item instrument.

RESULTS

Scores calculated using all three methods were highly correlated, but evidence of floor and ceiling effects was found with the standard scoring method. None of the subscales investigated proved valid. The 7-item instrument showed acceptable person separation reliability and good targeting and item performance.

CONCLUSIONS

Although standard scores and Rasch scores are highly correlated, Rasch analysis has the advantages of eliminating floor and ceiling effects and producing interval-scaled data. The Massof algorithm for approximation of the Rasch person measure performed well in this group of low-vision patients. The validity of the subscales VFQ-25 should be reconsidered.

Assessing visual activities of daily living in the visually impaired

PURPOSE

Visual function assessment questionnaires ask people to rate the difficulty they have performing visual activities of daily living (ADLs). This study examines the relationship between self-reported difficulty and actual performance in such ADLs.

METHODS

Twenty four subjects with established bilateral visual impairment initially self-reported their difficulty with 4 ADLs (reading newsprint, reading medicine labels, identifying coins and entering a PIN). Subjects' performance in variants of these ADLs was then assessed by measuring the time taken; by an observer rating subjects' performance; and by the subject rating their perceived difficulty with each specific task. Clinical visual function parameters were also assessed.

RESULTS

Varying the assessed ADL task changed how well the task correlated with self-reported difficulty. Clinical visual function, rate of task completion and observer rating of difficulty all correlated significantly with self-reported difficulty, explaining up to 69% of the variance in self-reported difficulty. However, despite replicating the ADLs as closely as possible in the clinical environment the perceived difficulty of the clinic tasks was rated as being less than the initial self-reported difficulty of the real-world task.

CONCLUSIONS

The task variant used is important when assessing functional visual performance directly. Timed and observer-rated methods of assessment can be appropriate for assessing functional vision. In this small study, the disconnect between self-reported visual difficulty and perceived or assessed difficulty suggests that functional performance is not the only factor influencing self-report, and responses to visual function assessment questionnaires should be interpreted in this light.