A method for determining a dioptric parameter includes: first, a test optical element having a dioptric function having a specific value of the dioptric parameter to be determined is provided and the person looks at a visual target using the test optical element； second, evaluation data and certitude data are collected, the evaluation data being indicative of the visual assessment expressed by the person looking at the visual target using the test optical element and certitude data being indicative of the degree of certainty of the person upon expressing the visual assessment. The first and second steps are repeated by varying the value of the dioptric parameter. For each value of the dioptric parameter tested a value a degree of certainty of the person is determined. The value of the dioptric parameter of the person is determined based on the values of degree of certainty of the person.
