OBJECTIVES: To assess the criterion validity of a patient reported visual function instrument (NEI-VFQ) in a cohort of low vision patients using clinical parameters. METHODS: A subset of the NEI-VFQ-51 items was administered to 255 low vision patients. Contrast sensitivity (CS), visual acuity (VA), reading acuity (RA), critical print size and maximum reading rate were measured. Retinal visual function was evaluated and foveal functioning assessed. The association of the NEI-VFQ subscales with clinical parameters were assessed by Pearson's correlation coefficients. Subscale scores between patients with stable/unstable vision loss and a functioning/non-functioning fovea were compared using Students T-test. Linear regression models were used to calculate the differences in scores that corresponded to a clinically significant three-line loss in visual acuity. RESULTS: Binocular VA was significantly correlated with the near vision (r=-0.56, p<0.0001) and distance vision subscales (r=-0.45, p<0.0001). Contrast sensitivity was moderately correlated with near vision (r=0.36, p<0.001) and more strongly correlated with distance vision (r=0.42, p<0.001). The maximum reading rate was significantly correlated with VA (r=0.53, p<0.0001). Patients with unstable visual loss reported a significantly lower mean composite score (6.0 points, p=0.03), expectation score (19.9 points, p<0.0001) and social functioning score (7.9 points, p=0.03) than patients with stable visual loss. Significant differences were found in the near (22.5 points, p<0.0001), distance (11.8 points, p=0.015), social functioning (15.5 points, p=0.015), and role limitations (17.0 points, p=0.009) subscales between patients with a functioning versus non-functioning fovea. A three-line difference in visual acuity was associated with a 5.8 to 10.9 point difference in the NEI-VFQ domains. CONCLUSION: The NEI-VFQ correlated significantly with reading speed and binocular visual acuity. Foveal functioning is significantly associated with the near and distance subscales, as well as reading speeds. A minimally important clinical difference of three lines of VA is associated with a 5.8-10.9 difference in NEI-VFQ scores.