Process for manufacturing an optical lens having a first face and a second face opposite said first face, comprising a step of positioning said second face relative to said first face for the machining of said second face, which positioning step comprises steps of: - providing a lens blank for forming said optical lens, which lens blank has an upper face for forming said first face, a lower face, opposite said upper face, for forming said second face, and at least one positioning guide; - providing a positioning ring having at least one control guide; - mounting said lens blank on said positioning ring; - positionally blocking said lens blank on a blocking and holding pin, said positioning ring then being interposed between said lens blank and said blocking and holding pin; said lens blank comprising a generally circular edge face forming a first mechanical positioning guide and at least one sloped portion forming a second mechanical positioning guide, said at least one sloped portion being located between said generally circular edge face and said upper face, said positioning ring having a generally cylindrical shape and comprising a cavity defining a generally circular internal outline forming a first complementary control guide, which internal outline is concentric with said edge face of said lens blank, and a shoulder forming a second complementary control guide; and said step of providing said lens blank comprising steps of: - edging at least partially the outline of said lens blank in order to form said generally circular edge face and thus form said first mechanical positioning guide of said lens blank; - characterized by the step of chamfering at least partially one portion of said lens blank, which portion is located between said generally circular edge face and said convex face, in order to form said at least one sloped portion and thus form said second mechanical positioning guide of said lens blank; and said step of mounting said lens blank on said ring comprises the step of at least partially lodging said lens blank in said cavity of said ring, with said edge face of said lens blank which is at least partially in contact with said internal outline of said ring and said at least one sloped portion of said lens blank which is also in contact with a ridge defined by said shoulder of said ring. - providing a lens blank for forming said optical lens, which lens blank has an upper face for forming said first face, a lower face, opposite said upper face, for forming said second face, and at least one positioning guide; - providing a positioning ring having at least one control guide; - mounting said lens blank on said positioning ring; - positionally blocking said lens blank on a blocking and holding pin, said positioning ring then being interposed between said lens blank and said blocking and holding pin; said lens blank comprising a generally circular edge face forming a first mechanical positioning guide and at least one sloped portion forming a second mechanical positioning guide, said at least one sloped portion being located between said generally circular edge face and said upper face, said positioning ring having a generally cylindrical shape and comprising a cavity defining a generally circular internal outline forming a first complementary control guide, which internal outline is concentric with said edge face of said lens blank, and a shoulder forming a second complementary control guide; and said step of providing said lens blank comprising steps of: said lens blank comprising a generally circular edge face forming a first mechanical positioning guide and at least one sloped portion forming a second mechanical positioning guide, said at least one sloped portion being located between said generally circular edge face and said upper face, said positioning ring having a generally cylindrical shape and comprising a cavity defining a generally circular internal outline forming a first complementary control guide, which internal outline is concentric with said edge face of said lens blank, and a shoulder forming a second complementary control guide; and said step of providing said lens blank comprising steps of: - edging at least partially the outline of said lens blank in order to form said generally circular edge face and thus form said first mechanical positioning guide of said lens blank; - characterized by the step of chamfering at least partially one portion of said lens blank, which portion is located between said generally circular edge face and said convex face, in order to form said at least one sloped portion and thus form said second mechanical positioning guide of said lens blank; and said step of mounting said lens blank on said ring comprises the step of at least partially lodging said lens blank in said cavity of said ring, with said edge face of said lens blank which is at least partially in contact with said internal outline of said ring and said at least one sloped portion of said lens blank which is also in contact with a ridge defined by said shoulder of said ring.