August Colenbrander

Assessment of functional vision and its rehabilitation

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.

Aspects of vision loss – visual functions and functional vision

To promote consistency in terminology, this paper explores the distinction between Visual Functions, which describe how the eye functions, and Functional Vision, which describes how the person functions in vision-related activities. Adequate assessment of Functional Vision is essential to measure outcomes of vision rehabilitation. Consistent measurement will require the development of a unified set of criteria, better suited to use in rehabilitation than the current ‘participation’ categories in International Classification of Functioning (ICF). Whether vision tests are used to explore the underlying causes of eye disease or their functional consequences affects the ways in which they are administered and interpreted. This is explored in detail for letter-chart acuity (the most common visual function test) and reading (the most common functional vision test). At the group level a statistical relationship between visual functions and functional vision can be shown, but individual variations are too great t...

The historical evolution of visual acuity measurement

This review aims at uncovering certain aspects of the historical evolution of a subject that is so familiar that we rarely stop to think about its background. That subject is Visual Acuity Measurement. The history will show how innovative ideas that were ignored when first proposed were eagerly adopted when they were reintroduced later. It will also show the role of vision rehabilitation in preparing the way for the current standards.

Contrast sensitivity and visual hallucinations in patients referred to a low vision rehabilitation clinic.

Contrast sensitivity and visual hallucinations have significant consequences for the patient The paper on contrast sensitivity and visual hallucinations by Jackson et al 1 ( see page 296 ) in this issue draws attention to the fact that we will never detect correlations among factors to which we do not pay attention or that we are not interested in. Both contrast sensitivity and visual hallucinations are items that are too often omitted from the medical history and the eye examination. One of the reasons probably is that neither finding can contribute much to the differential diagnosis. However, both conditions have significant consequences for the patient. Many people who experience visual hallucinations are deeply concerned and afraid that it is a sign of some mental deterioration. They are greatly relieved to find out that this phenomenon is well know, has …