Konrad Pesudovs - Visual Disability Assessment (VDA)

cataract 1

An instrument for assessment of subjective visual disability in cataract patients

Aims/background: The construction and validation of an instrument for the assessment of subjective visual disability in the cataract patient is described. This instrument is specifically designed for measuring the outcome of cataract surgery with respect to visual disability.

Methods: Visually related activities thought to be affected by cataract were considered for the questionnaire. These were reduced by pilot study and principal components analysis to 18 items. A patient's assessment of his/her ability to perform each task was scored on a four point scale. Scores were averaged to create an overall index of visual disability, as well as subscale indices for mobility related disability, distance/lighting/reading related disability, and near and related tasks visual disability. The questionnaire, administered verbally is entitled "The Visual Disability Assessment (VDA)". Reliability testing included test-retest reliability, interobserver reliability (, the intraclass correlation coefficient), and internal consistency reliability (Cronbach's ). Construct validation, the process for proving that a test measures what it is supposed to measure, included consideration of content validity, comparison with the established Activities of Daily Vision Scale (ADVS) and empirical support with factor analysis.

Results: For the four indices, interobserver reliability varied from 0.92 to 0.94, test-retest reliability varied from 0.96 to 0.98, and internal consistency reliability varied from 0.80 to 0.93. The VDA compared favourably with the ADVS by correlation, but Bland-Altman analysis demonstrated that the two instruments were not clinically interchangeable. Factor analysis suggests that all test items measure a common theme, and the subgroupings reflect common themes.

Conclusions: The VDA is easy to administer because it has a short test time and scoring is straightforward. It has excellent interobserver, test-retest, and internal consistency reliability, and compares favourably with the ADVS, another test of visual disability. Factor analysis demonstrated that the 18 items measure a related theme, which can be assumed to be visual disability. The VDA is a valid instrument which provides a comprehensive assessment of visual disability in cataract patients

Table 1. Activities listed in the visual disability assessment. The patient is asked: "To what extent, if at all, does your vision interfere with your ability to carry out the following activities?" The patient is asked to take into account both the degree to which they can perform each task as well as the extra effort involved. Assessment of visual disability is done for both eyes open and habitual spectacle correction is worn. The scoring system is included. All are counted for the total score, those marked with m are included in the mobility score, those marked with d are included in the distance/lighting/reading score, and those marked with n are included in the near and related tasks score

Activity	Not at all (1)	A little (2)	Quite a bit (3)	A lot (4)

Reading^d,n	1	2	3	4
Seeing in the distance^d	1	2	3	4
Recognising faces across the street^d	1	2	3	4
Watching TV^d	1	2	3	4
Seeing in bright light/glare^d	1	2	3	4
Seeing in poor or dim light^{d, n}	1	2	3	4
Appreciating coloursⁿ	1	2	3	4
Driving a car, by day^d	1	2	3	4
Driving a car, by night^d	1	2	3	4
Walking inside^m	1	2	3	4
Walking outside^m	1	2	3	4
Using steps^m	1	2	3	4
Crossing the road^m	1	2	3	4
Using public transport^m	1	2	3	4
Travelling independently^m	1	2	3	4
Moving in unfamiliar surroundingsⁿ	1	2	3	4
Employment/housework activitiesⁿ	1	2	3	4
Hobbies/leisure activitiesⁿ	1	2	3	4

Br J Ophthalmol 1998;82:617-624

Konrad Pesudovs, Douglas J Coster
Department of Ophthalmology, Flinders Medical Centre and Flinders University of
South Australia, Australia

Accepted for publication: 9 December 1997

VDA as PDF (230 Kb)

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