Patent ID: 6934084

Claim:
A composite prism functioning as an ophthalmic prism for diagnosing and correcting visual disorders, operating as an exclusively transmission device, having prismatic power in the range of fifteen prism diopters to fifty prism diopters, operating and being optically transmissive over a bandwidth of at least 150 nm within the visible spectrum, said spectrum being defined as the spectral band of wavelengths between 380 mm and 780 mm, such composite prism comprising: a transparent refractive prismatic component having an entrance face, an exit face and a refractive index of at least 1.49; a blazed transmission diffraction grating having a uniform grating period and a low blaze angle; means for retaining the diffraction grating against one of the entrance and exit faces of the transparent refractive prismatic component wherein the diffraction grating is oriented in such a manner that the prismatic power of the composite prism is approximately the sum of the prismatic powers of the transparent refractive prismatic component and the diffraction grating.