The aim of this study is to build up a verbal protocol technique for samples of visual impaired users in order to overcome the limits of concurrent and retrospective protocols. Indeed, when blind users surf using a screen reader and talk about the way they interact with the computer, the evaluation is influenced by a structural interference. Users are force to think aloud and listen to the screen reader at the same time. The technique we improved, called Partial Concurrent Thinking Aloud (PCTA), integrates a modified set of concurrent verbalization and retrospective analysis. One group of 6 blind user and another group of 6 sighted users evaluated the usability of a website by PCTA. Estimating the number of users needed with an asymptotic test, we found out that the two groups had an equivalent ability of identifying usability problems, both over 80%. The result suggest that PCTA, even respecting the properties of classic verbal protocols, also allows to overcome the structural interference and the limits of concurrent and retrospective protocols when used with screen-reader users.