Quality of Vision Index: a new method to appraise visual function changes in age-related macular degeneration

To explore the correlation between psychophysical measures of visual function and vision-related quality of life (QOL) in exudative age-related macular degeneration (AMD) and to obtain a new quality of vision index expressed as corrected visual acuity (cVA) that is scaled like visual acuity (VA), but that incorporates the weighted contribution of VA, contrast sensitivity (CS), and reading ability.

Visual acuity, CS, and reading ability were measured in 293 patients with AMD in this multicenter prospective study. Vision-related QOL was quantified by the 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25). The validity of the questionnaire was assessed using Rasch analysis. The relationship between psychophysical tests and NEI-VFQ-25 scores was investigated. A cVA index was developed integrating Rasch-scaled NEI-VFQ-25 score with VA, CS, and reading ability as a tool to be used for evaluating vision-related QOL on the same scale as VA.

A total of 27.5% of the variability of VFQ score was found to be explained by VA alone in patients with AMD. The proportion of Rasch-scaled QOL estimate variance explained by cVA was 33.2% as compared to 27.5% explained by VA and 24.5% by CS, which was a statistically significant improvement in both cases (p=0.015 and p<0.001, respectively). The correlation of reading ability with vision-related QOL was largely mediated by VA and CS and therefore it was not retained in the vision index.

Visual acuity is poorly correlated with vision-related QOL in patients with AMD. Even though the new cVA index is a new method which better correlates with vision-related QOL, the major components of the individual perception of vision remain unexplained by common psychometric tests.