The Quality of Vision questionnaire: subscale interchangeability.

PURPOSE: The purpose of this study is to evaluate the interchangeability of the three subscales of the Quality of Vision (QoV) questionnaire: Frequency, Severity and Bothersome. This will indicate if any of the subscales are predictive of one another and whether respondents need to complete all three subscales.

METHODS: Data from four studies were pooled together, totaling 1930 completed questionnaires. Patient groups consisted of spectacle wearers, contact lens wearers, post-laser refractive surgery (including laser in situ keratomileusis, laser-assisted subepithelial keratectomy, and photorefractive keratectomy surgeries for various refractive errors), patients with cataract, and patients having undergone lens implantation surgery (consisting of monofocal, multifocal, and pseudoaccommodative intraocular lenses). The Bland-Altman limits of agreement (LoA) method was used to assess the interchangeability between the three subscales of the QoV questionnaire.

RESULTS: The mean difference, standard deviation of the differences, and the LoA for the Frequency versus Severity subscale was 2.8570, 6.784, and -10.4397 to 16.1537, respectively. The mean difference, standard deviation of the differences, and the LoA for the Frequency versus Bothersome subscale was 5.4674, 12.5768, and -19.1831 to 30.1179, respectively. The mean difference, standard deviation of the differences, and the LoA for the Severity versus Bothersome subscale was 2.6104, 9.4444, and -15.9006 to 21.1213, respectively.

CONCLUSIONS: The wide LoA found in this study indicate that the three subscales of the QoV questionnaire (Frequency, Severity and Bothersome.) measure different aspects of the latent trait, quality of vision. Users should continue to use all three subscales of the questionnaire to achieve a comprehensive assessment of subjective quality of vision.