A single-piece patient interface device (PI) for coupling an patient's eye to an ophthalmic surgical laser system, which includes a rigid shell, a flexible suction ring joined to a lower edge of the shell, an applanation lens, and a flexible annular diaphragm which joins the applanation lens to the shell near the lower edge of the shell. The flexible diaphragm allows the applanation lens to move relative to the shell, including to shift in longitudinal and lateral directions of the shell and to tilt. In operation, the surgeon first secures the PI to the patient's eye by hand, and then couples the laser system to the PI by lowering the laser delivery head into the PI shell. During the lowering process, the laser delivery head presses the applanation lens down relative to the PI to applanate the cornea of the eye.
