A cast mould for the purpose of manufacturing a contact lens or an intraocular lens, the cast mould being is provided with: • a first cast mould half comprising: ∘ an optically accurately defined surface; ∘ first positioning means: • a second cast mould half comprising: ∘ a central part with optically accurately defined surface; ∘ a bearing ring which surrounds the central part and which is provided with second positioning means which are designed for engagement of the first positioning means (16 - 18) for holding the cast mould under a bias in a closed position in which the first and the second cast mould halves (12, 20) are clamped onto each other, wherein a central axis of the second cast mould half extends perpendicularly to the plane in which the bearing ring extends and intersects a centre of the bearing ring; and characterized by: ∘ a thin-walled, flexible connection (30a, 30b) which extends between the bearing ring and the central part and which connects the central part with the bearing ring, wherein a wall thickness of the thin-walled, flexible connection (30a, 30b) is less than 0.2 times the thickness of the central part at the location of the central axis and preferably even less than 0.1 times the thickness of the central part at the location of the central axis. • a first cast mould half comprising: ∘ an optically accurately defined surface; ∘ first positioning means: ∘ an optically accurately defined surface; ∘ first positioning means: • a second cast mould half comprising: ∘ a central part with optically accurately defined surface; ∘ a bearing ring which surrounds the central part and which is provided with second positioning means which are designed for engagement of the first positioning means (16 - 18) for holding the cast mould under a bias in a closed position in which the first and the second cast mould halves (12, 20) are clamped onto each other, wherein a central axis of the second cast mould half extends perpendicularly to the plane in which the bearing ring extends and intersects a centre of the bearing ring; and characterized by: ∘ a thin-walled, flexible connection (30a, 30b) which extends between the bearing ring and the central part and which connects the central part with the bearing ring, wherein a wall thickness of the thin-walled, flexible connection (30a, 30b) is less than 0.2 times the thickness of the central part at the location of the central axis and preferably even less than 0.1 times the thickness of the central part at the location of the central axis. ∘ a central part with optically accurately defined surface; ∘ a bearing ring which surrounds the central part and which is provided with second positioning means which are designed for engagement of the first positioning means (16 - 18) for holding the cast mould under a bias in a closed position in which the first and the second cast mould halves (12, 20) are clamped onto each other, wherein a central axis of the second cast mould half extends perpendicularly to the plane in which the bearing ring extends and intersects a centre of the bearing ring; and ∘ a thin-walled, flexible connection (30a, 30b) which extends between the bearing ring and the central part and which connects the central part with the bearing ring, wherein a wall thickness of the thin-walled, flexible connection (30a, 30b) is less than 0.2 times the thickness of the central part at the location of the central axis and preferably even less than 0.1 times the thickness of the central part at the location of the central axis.