Purpose:
Performance-based measures may provide an objective assessment of how glaucoma affects daily functioning. We sought to validate a clinically applicable performance-based measure of visual ability for patients with glaucoma in South India and describe its relationship to clinical and patient-reported outcomes.

Design:
Cross-sectional validation study.

Participants:
One hundred forty-five participants with glaucoma recruited at Aravind Eye Hospital.

Methods:
We modified the Compressed Assessment of Ability Related to Vision (CAARV), a performance-based measure validated in the United States, to be culturally relevant in South India. Participants underwent a series of tests, including the Indian CAARV (I-CAARV), Indian Visual Functioning Questionnaire (IND-VFQ), Spaeth/Richman Contrast Sensitivity (SPARCS) test, standard automated perimetry, and visual acuity (VA) assessment. Factor analysis and Rasch modeling were used to validate the I-CAARV. Correlations between the I-CAARV results and other outcomes were evaluated.

Main Outcome Measure:
Psychometric properties of the I-CAARV for individuals with glaucoma in South India.

Results:
The study included 142 participants (51.7% women; mean age, 56.4 years). Average presenting VA and visual field (VF) mean deviation (MD) in the better-seeing eye were 0.26 logarithm of the minimum angle of resolution and -6.57 dB, respectively. The 4 tasks of the I-CAARV were found to measure a single underlying construct. Rasch analysis of the I-CAARV revealed that the outcome measure had moderate reliability, good construct and content validity, and fair measurement precision. Tasks were well targeted to the study sample. Rasch-calibrated scores on the I-CAARV were correlated significantly with Rasch-calibrated IND-VFQ scores (r = -0.54) and VF MD, presenting VA, best-corrected VA, and SPARCS contrast sensitivity in both the better-seeing eye (r = 0.60, r = -0.51, r = -0.53, and r = 0.76, respectively) and worse-seeing eye (r = 0.48, r = -0.61, r = -0.46, r = 0.69, respectively).

Conclusions:
The I-CAARV is a valid performance-based measure of vision-dependent functioning in glaucoma in South India. This study also found that I-CAARV task performance was correlated strongly with contrast sensitivity and suggested that performance-based and patient-reported outcomes are related but distinct measures of the impact of glaucoma on functioning and vision-related quality of life. Future studies are needed to determine the sensitivity of the I-CAARV to detect changes because of disease progression that are relevant to functioning and vision-related quality of life.