The invention relates to a pressure sensor comprising a housing (12), a membrane (26) arranged in said housing and which can be deflected by the pressure to be measured, a light source (LED) having an optical axis, a light detector having an optical axis and a light blocker (36) that is coupled to the membrane and that can be deflected thereby, the blocker being arranged in the beam path of the light source. The light source and the light detector are arranged inside the housing (12), wherein their optical axes lie parallel to one another. A first prism (40) is assigned to the light source and a second prism (42) is assigned to the light detector in such a way that an uninterrupted beam path from the light source through both prisms to the light detector is obtained. To this end, the light blocker (36) is arranged between the two prisms.