The invention relates to a patient interface (1) and an ophthalmological diagnosis and/or treatment system (100), as well as to a method for fixing a relative geometric position of an eye (A1) in relation to an ophthalmological diagnosis and/or treatment system (100). The problem addressed by the invention is describing devices and methods that permit a safe suction and fixing of the eye (A1) at a low negative pressure. This problem is solved by: a patient interface (1) designed, in practice, to form a limited volume (V1) via which diagnostic and/or therapeutic radiation can be transmitted and in which a negative pressure can be generated a container (2) for a patient interface (1) and an applicator (5), which permit the formation of a volume (V1) of this type an ophthalmological diagnosis and/or treatment system (100) having a patient interface (1) of this type and a corresponding method.
