The present invention relates to a device for monitoring an eye of a subject, comprising: a transparent carrier for being in contact with the eye of the subject； and a photosensor facing the eye of the subject for receiving light reflected from the eye of the subject and for determining a light intensity of the received light, wherein the photosensor is arranged on the transparent carrier； and wherein the photosensor includes one of: a plurality of photodetectors arranged in the form of a two-dimensional array and spaced apart from one another for allowing incident light to pass between the photodetectors to enter the eye of the subject wherein the plurality of photodetectors is arranged in a plurality of rows of photodetectors or in a plurality of concentric circles substantially covering the iris and the pupil of the eye of the subject； and a single large area photodetector covering an iris and a pupil of the eye of the subject. The present invention further relates to a system and method for monitoring a pain level of a subject comprising a device as defined above.
