Assessment of functional vision and its rehabilitation

Abstract

. This article, based on a report prepared for the International Council of Ophthalmology (ICO) and the International Society for Low Vision Research and Rehabilitation (ISLRR), explores the assessment of various aspects of visual functioning as needed to document the outcomes of vision rehabilitation. Documenting patient abilities and functional vision (how the person functions) is distinct from the measurement of visual functions (how the eye functions) and also from the assessment of quality of life. All three areas are important, but their assessment should not be mixed. Observation of task performance offers the most objective measure of functional vision, but it is time‐consuming and not feasible for many tasks. Where possible, timing and error rates provide an easy score. Patient response questionnaires provide an alternative. They may save time and can cover a wider area, but the responses are subjective and proper scoring presents problems. Simple Likert scoring still predominates but Rasch analysis, needed to provide better result scales, is gaining ground. Selection of questions is another problem. If the range of difficulties does not match the range of patient abilities, and if the difficulties are not distributed evenly, the results are not optimal. This may be an argument to use different outcome questions for different conditions. Generic questionnaires are appropriate for the assessment of generic quality of life, but not for specific rehabilitation outcomes. Different questionnaires are also needed for screening, intake and outcomes. Intake questions must be relevant to actual needs to allow prioritization of rehabilitation goals; the activity inventory presents a prototype. Outcome questions should be targeted at predefined rehabilitation goals. The Appendix cites some promising examples. The Low Vision Intervention Trial (LOVIT) is an example of a properly designed randomized control study, and has demonstrated the remarkable effectiveness of vision rehabilitation. It is hoped that further similar studies will follow.

Relationship between functional vision and balance and mobility performance in community-dwelling older adults

“…how the eye functions, and functional vision, i.e. how vision deficits may affect functioning in daily and social activities (Colenbrander 2010).…”

Visual task performance in the blind with the BrainPort V100 Vision Aid

“…Acuities were found to average 20/ 430 in a group of 6 untrained, blind subjects [47], corresponding to a minimum angle of resolution (logMAR) of 1.34. A visual acuity of 20/430 can be considered a 'moderate-tosevere vision loss,' according to the International Classification of Diseases (ICD) [46]. However, the field of view (FOV) of the camera was not reported in this study.…”

“…Visual acuity tests based on Snellen charts are the gold standard to determine visual function in the clinic [46]. However, current artificial vision devices produce only rudimentary visual percepts, making the use of resolution acuity tasks somewhat problematic.…”

“…The study group of 15 blind subjects received 10 min of task-specific training. The average acuity was 2.31 logMAR (20/4120 Snellen equivalent), which classifies as 'near-blindness' according to the ICD [46]. The term 'ultralow vision' has recently been introduced to describe such rudimentary forms of visual function [16].…”

“…As a result, tactile visual acuities could often not be determined due to the stimulus size reaching the maximum available size in the software [16]. The largest optotypes used corresponded to 2.59 logMAR (20/7800) and all subjects had thresholds at, or above this angle in the Landolt C test after training, which corresponds to ultralow vision [16], or near-blindness on the ICD scale [46]. On the tumbling 'E' test, subjects scored slightly better, and the median acuity was 2.57 logMAR (20/7400) after training.…”