Metrics of retinal image quality predict optimal refractive corrections and correlate with visual performance. To date, they do not predict absolutely the relative change in visual performance when aberrations change and therefore need to be a-posteriori rescaled to match relative measurements. Here we demonstrate that a recently proposed metric can be used to predict, in an absolute manner, changes in contrast sensitivity measurements with Sloan letters when aberrations change. Typical aberrations of young and healthy eyes (for a 6 mm pupil diameter) were numerically introduced, and we measured the resulting loss in contrast sensitivity of subjects looking through a 2 mm diameter pupil. Our results suggest that the metric can be used to corroborate measurements of visual performance in clinical practice, thereby potentially improving patient follow-ups.