A novel visual analogue scale (VAS) device: an instrument based on the VAS designed to quantify the subjective visual experience

Purpose: To evaluate a novel device intended to facilitate the direct quantification of the subjective visual experience. The design principle is based on that of the visual analogue scale (VAS) technique but obviates the need for subsequent measurement unlike the administration of the conventional paper VAS. Methods: The visual experience of 134 normally sighted 17-40-year-olds was quantified using (in randomised sequence) a paper VAS and the novel VAS device. A notional 100-point scale was utilised in either case, and the extreme descriptive anchors for both instruments were 'dreadful' and 'perfect'. Results: The degree of clinical agreement between the two alternative VAS techniques was very high. A small bias (mean = +0.7 VAS units: 95% confidence interval 0.3-1.2 units) towards the paper VAS was evident in these data, an outcome of no clinical significance or impediment as regards the substitution of the novel device for the conventional paper-based approach. Conclusions: The moving of a bead along a wire is shown to be a clinically and statistically reliable alternative procedure to the pen-marking of a conventional paper VAS for the evaluation of the recent subjective visual experience, provided that the same minimum/maximum descriptive anchors are used for either instrument. The instant quantification of the VAS score afforded by the novel technique introduced here broadens the potential clinical application of this technique.