Resumen: We introduce a new type of lens with two gradients of refractive index (GRIN) and of curvature (GRCU) of iso-indicial surfaces, i.e., GRINCU. The inner structure of the lens resembles that of an onion. Each layer is a meniscus lens with infinitesimal thickness, which coincides with an iso-indicial surface characterized by a conicoid shape and a constant refractive index. The internal distribution automatically adapts to the external geometry. Here, we consider the simplest case of a constant gradient of the curvature radius -G, which indicates a linear decrease as we move along the optical axis. The formulation of this type of lens is presented, including its generalization to nonrotationally symmetric conicoid surfaces. The formulation is then applied to model the crystalline lens; the code corresponding to the numerical computation of the 3D refractive index distribution as well as its gradient is provided as a supplementary file. Finally, we confirmed a refractive power increase of nearly 14% when G changes from 0 to 3. Idioma: Inglés DOI: 10.1364/OE.435266 Año: 2021 Publicado en: OPTICS EXPRESS 29, 20 (2021), 30998-31009 ISSN: 1094-4087 Factor impacto JCR: 3.833 (2021) Categ. JCR: OPTICS rank: 28 / 100 = 0.28 (2021) - Q2 - T1 Factor impacto CITESCORE: 7.3 - Physics and Astronomy (Q1)