An apparatus for monitoring one or more parameters of the eye of a patient over multiple sessions which are temporally spaced apart and between which the eye of the patient can have moved, said apparatus comprising: a camera for taking one or more images of the eye; an illumination unit for illuminating the eye by a ring-shaped light pattern to generate corneal reflections, said illumination unit being preferably located such that the center of the ring is coaxial with the optical axis of the camera; a module for determining during a first session the location of the corneal reflections in the image of the eye; a module for determining during said first session based on said determined location of the corneal reflections, at least one further parameter of the eye and its coordinates in a first coordinate system based on a geometrical model representing the eye as a spherical eyeball having a spherically shaped cornea mounted thereon; a module for determining during a second session temporally spaced apart from said first session said location of said corneal reflections of the eye and based thereon said further eye parameter and its coordinates in a second coordinate system; a module for determining the eye motion in six degrees of freedom between said first and said second session and for determining a coordinate transformation based thereon; a module for transforming based on said determined eye motion said further eye parameter and its coordinates from said first coordinate system into said second coordinate system; a module for quantifying and/or visualizing the change of said further eye parameter between said first and said second session based on said further parameter and its coordinates measured during said second session and said transformed parameter and its coordinates measured during said first session. a camera for taking one or more images of the eye; an illumination unit for illuminating the eye by a ring-shaped light pattern to generate corneal reflections, said illumination unit being preferably located such that the center of the ring is coaxial with the optical axis of the camera; a module for determining during a first session the location of the corneal reflections in the image of the eye; a module for determining during said first session based on said determined location of the corneal reflections, at least one further parameter of the eye and its coordinates in a first coordinate system based on a geometrical model representing the eye as a spherical eyeball having a spherically shaped cornea mounted thereon; a module for determining during a second session temporally spaced apart from said first session said location of said corneal reflections of the eye and based thereon said further eye parameter and its coordinates in a second coordinate system; a module for determining the eye motion in six degrees of freedom between said first and said second session and for determining a coordinate transformation based thereon; a module for transforming based on said determined eye motion said further eye parameter and its coordinates from said first coordinate system into said second coordinate system; a module for quantifying and/or visualizing the change of said further eye parameter between said first and said second session based on said further parameter and its coordinates measured during said second session and said transformed parameter and its coordinates measured during said first session.