The invention relates to a system for determining a value of a magnitude associated with a subjective value of an optical feature of at least a corrective lens adapted to an eye of a subject, by implementing a subjective test where the subject is asked to describe his visual performance in a plurality of real optical conditions by choosing one descriptive answer among a set of possible descriptive answers, comprising a computer with one or more memory and one or more processor, wherein:
- an initial model giving the probability of each descriptive answer of the set of descriptive answers for each theoretical optical condition of a plurality of theoretical optical conditions is stored in one of said one or more memory of said computer,
- said one or more processor of said computer is programmed to:
a) collect (500) the results of said subjective test, performed by asking the subject to describe his visual performance in each real optical condition of said plurality of real optical conditions by choosing, for each real optical condition, one descriptive answer among said set of possible descriptive answers, said results comprising each descriptive answer chosen and the corresponding real optical condition,
b) determine (800, 900) the value of said magnitude by taking into account said initial model and each descriptive answer collected.