Disease-specific assessment of Vision Impairment in Low Luminance in age-related macular degeneration - a MACUSTAR study report

Abstract

Background/aims: To further validate the Vision Impairment in Low Luminance (VILL) questionnaire, which captures visual functioning and vision-related quality of life (VRQoL) under low luminance, low-contrast conditions relevant to age-related macular degeneration (AMD).

Methods: The VILL was translated from German into English (UK), Danish, Dutch, French, Italian and Portuguese. Rasch analysis was used to assess psychometric characteristics of 716 participants (65% female, mean age 72±7 years, 82% intermediate AMD) from the baseline visit of the MACUSTAR study. In a subset of participants (n=301), test-retest reliability (intraclass correlation coefficient (ICC) and coefficient of repeatability (CoR)) and construct validity were assessed.

Results: Four items were removed from the VILL with 37 items due to misfit. The resulting Vision Impairment in Low Luminance with 33 items (VILL-33) has three subscales with no disordered thresholds and no misfitting items. No differential item functioning and no multidimensionality were observed. Person reliability and person separation index were 0.91 and 3.27 for the Vision Impairment in Low Luminance Reading Subscale (VILL-R), 0.87 and 2.58 for the Vision Impairment in Low Luminance Mobility Subscale (VILL-M), and 0.78 and 1.90 for the Vision Impairment in Low Luminance Emotional Subscale (VILL-E). ICC and CoR were 0.92 and 1.9 for VILL-R, 0.93 and 1.8 for VILL-M and 0.82 and 5.0 for VILL-E. Reported VRQoL decreased with advanced AMD stage (p<0.0001) and was lower in the intermediate AMD group than in the no AMD group (p≤0.0053).

Conclusion: The VILL is a psychometrically sound patient-reported outcome instrument, and the results further support its reliability and validity across all AMD stages. We recommend the shortened version of the questionnaire with three subscales (VILL-33) for future use.

Trial registration number: NCT03349801.

Keywords: Diagnostic tests/Investigation; Macula.

Figure 1

Bland-Altman plots of the VILL-33 test and retest data: (A) reading and accessing information subscale, (B) mobility and safety subscale and (C) emotional well-being subscale. AMD, age-related macular degeneration; iAMD, intermediate age-related macular degeneration; VILL-33, Vision Impairment in Low Luminance with 33 items.

Figure 2

Distributions of VILL-33 person measures across different age-related macular degeneration stages: (A) reading and accessing information subscale, (B) mobility and safety subscale and (C) emotional well-being subscale. VILL, Vision Impairment in Low Luminance; VILL-33, Vision Impairment in Low Luminance with 33 items.