A disk enabling modification of the power of an optical component consists of a Fresnel lens. The disk is initially formed with a general rounded shape which corresponds to the shape of the optical component. In this way, the disk does not lose its shape or does not lose it very much when it is applied against the component. It does not cause image distortion or optical aberration when an object is observed through the component provided with the disk. Such a disk is particularly adapted to obtain correction of ametropia or to a solar mask initially lacking optical power.