Method for manufacturing an ophthalmic element comprising a film structure

A method for manufacturing an ophthalmic element comprising a vision base element and a film structure that is adhered permanently to a curved optical surface of the vision base element, so that the film structure conforms to said optical surface, the method comprising the following steps:

• /1/ providing the film structure so that said film structure has a useful area suitable for covering partially or entirely the optical surface of the vision base element, and said film structure comprising at least one film having a sacrificial film portion that extends beyond the useful area from at least part of a peripheral limit of said useful area;
• /2/ bonding the film structure to the optical surface of the vision base element, so that the peripheral limit of the useful area of the film structure matches a peripheral limit of the optical surface of the vision base element;
• then
• /3/ separating the sacrificial film portion from the useful area of the film structure, so that the film structure becomes limited to within the useful area in the ophthalmic element,
• wherein at least part of the sacrificial film portion is auxetic, so that a Poisson ratio ν of said part of the sacrificial film portion is negative, said Poisson ratio ν being defined as:
• v
• =
• -
• ε
• trans
• ε
• axial
• wherein εtrans is a relative transverse strain of the auxetic part of the sacrificial film portion, and εaxial is a relative axial strain of the auxetic part of the sacrificial film portion, said relative transverse strain and relative axial strain being positive for increases in transverse dimension and axial dimension, respectively, of the auxetic part of the sacrificial film portion, or being negative for decreases in said transverse dimension and axial dimension, respectively, of the auxetic part of the sacrificial film portion.