Method and apparatus for locally measuring refractive characteristics of a lens in one or several specific points of said lens

An apparatus for measuring at least one refractive characteristic of a lens (L) at at least one specific point of said lens, the apparatus comprising:

• a support (40) arranged to receive said lens, on its own or mounted in a frame;
• on a first side of said support, lighting means (21) including an optical system for generating a collimated light beam (28) directed towards the lens (L) under measurement installed on said support;
• on one side or the other of the support (40), detachment means (23) for detaching light rays (35) from the light beam, suitable for detaching a localized group of at least three non-coplanar light rays (35) grouped together about a measurement axis (37) in a measurement cylinder of section that is substantially smaller than the section of the lens (L) under measurement;
• on a second side of the support (40), acquisition means (30) suitable for identifying the deflections imparted by the lens (L) under measurement on said detached light rays and for delivering a signal representative of said deflections;
• and
• an electronic and computer system (50) programmed to deduce from said deflections the value of the refractive characteristic of the lens (L) under measurement at the measurement point;
• the apparatus being characterized in that the support (40) is stationary relative to the beam (28) coming from the lighting means, and the detachment means (23) for detaching the light rays possess variable geometry controlled by the electronic and computer system (50) to modify the position of the measurement axis (37) as a function of the position of the measurement point.