A contact lens shaped measuring device comprises a sensor having a protrusion towards the cornea. The measuring device is flexible to a degree that it is flattened by a closing eye lid and the protrusion creates an indentation of the cornea. The force on the protrusion is measured by the sensor. Applying a constant lid acceleration/deceleration model to the movement of the lid and a mechanical model to the cornea, the tension of the cornea is determined and deduced from the force measured with the lid closed, yielding the true intraocular pressure. In an alternative, the protrusion is characterized by a discontinuity in its shape, or the sensor is subdivided, each subsensor being characterized by a protrusion of different shape. With the values obtained as extrema and at the discontinuity or with different protrusions, the tension of the cornea can be obtained by a (linear) extrapolation.