Abstract: The invention relates to a device for optical measurement of a thickness of an intransparent layer on a substrate, comprising first means for optical distance measurement configured to measure a first distance between a first reference plane and a first surface of the intransparent layer, and second means for optical distance measurement configured to measure a second distance between a second reference plane and a second surface of the intransparent layer. The second means measures a third distance between the second reference plane and a surface of the substrate. The thickness of the intransparent layer is computed from the first distance and the second distance. The measurement of the third distance is used to take into account the influence of the optical effect of the substrate on the distance measurement of the second distance. The invention also relates to a method for optical measurement of a thickness of an intransparent layer on a substrate.