Method for the addition of a functional coating on an optical surface of an existing spectacle lens mounted in a spectacle frame or dismounted from said frame, said optical surface being the optical surface of the existing outermost coating layer deposited on the optical substrate of the spectacle lens, said method comprising the following steps: - providing a first set of rules suitable to determine if the features of an optical surface chosen within a list of features are compatible with a functional coating chosen within a list of functional coatings, and a second set of rules to determine a modified optical surface if features of an optical surface and a functional coating are not compatible; - providing said spectacle lens; wherein said spectacle lens: o is mounted in the spectacle frame, or o has been previously dismounted from the spectacle frame; - choosing within the list of functional coatings a functional coating to be added on said optical surface; - carrying a diagnostic of the spectacle lens, comprising analysing the quality of the optical surface and identifying the features of the optical surface, wherein said analysing comprises steps for detecting, quantifying and localising defects on the optical surface; - determining thanks to the first set of rules if the features of the optical surface and the chosen functional coating are compatible; - if the optical surface has features compatible with the chosen functional coating, depositing the chosen functional coating on the optical surface; - if the optical surface has features not compatible with the chosen functional coating, forming a modified optical surface which is compatible with the chosen functional coating determined thanks to the second set of rules and depositing the chosen functional coating on the modified optical surface; wherein the list of functional coatings consists of: - an anti-soiling coating, - an anti-reflective coating, - an anti-dust coating, - an anti-fog coating, - a water repellent coating, - an anti-scratch coating, - an impact-resistant coating, - an interferential filter, - a tinted coating, - a mirror coating, - a photochromic coating, - a polarized coating, - a filter coating, and - a combination of any of preceding compatible coatings, wherein the features of an optical surface is chosen within the list consisting of: - chemical composition of the optical surface, - nature of the optical surface, - type of material on the surface of the optical surface wherein the type of material is selected within the list consisting of metal oxide, silica, varnish. - providing a first set of rules suitable to determine if the features of an optical surface chosen within a list of features are compatible with a functional coating chosen within a list of functional coatings, and a second set of rules to determine a modified optical surface if features of an optical surface and a functional coating are not compatible; - providing said spectacle lens; wherein said spectacle lens: o is mounted in the spectacle frame, or o has been previously dismounted from the spectacle frame; o is mounted in the spectacle frame, or o has been previously dismounted from the spectacle frame; - choosing within the list of functional coatings a functional coating to be added on said optical surface; - carrying a diagnostic of the spectacle lens, comprising analysing the quality of the optical surface and identifying the features of the optical surface, wherein said analysing comprises steps for detecting, quantifying and localising defects on the optical surface; - determining thanks to the first set of rules if the features of the optical surface and the chosen functional coating are compatible; - if the optical surface has features compatible with the chosen functional coating, depositing the chosen functional coating on the optical surface; - if the optical surface has features not compatible with the chosen functional coating, forming a modified optical surface which is compatible with the chosen functional coating determined thanks to the second set of rules and depositing the chosen functional coating on the modified optical surface; wherein the list of functional coatings consists of: - an anti-soiling coating, - an anti-reflective coating, - an anti-dust coating, - an anti-fog coating, - a water repellent coating, - an anti-scratch coating, - an impact-resistant coating, - an interferential filter, - a tinted coating, - a mirror coating, - a photochromic coating, - a polarized coating, - a filter coating, and - a combination of any of preceding compatible coatings, - an anti-soiling coating, - an anti-reflective coating, - an anti-dust coating, - an anti-fog coating, - a water repellent coating, - an anti-scratch coating, - an impact-resistant coating, - an interferential filter, - a tinted coating, - a mirror coating, - a photochromic coating, - a polarized coating, - a filter coating, and - a combination of any of preceding compatible coatings, wherein the features of an optical surface is chosen within the list consisting of: - chemical composition of the optical surface, - nature of the optical surface, - type of material on the surface of the optical surface wherein the type of material is selected within the list consisting of metal oxide, silica, varnish. - chemical composition of the optical surface, - nature of the optical surface, - type of material on the surface of the optical surface wherein the type of material is selected within the list consisting of metal oxide, silica, varnish.