A gaze-tracking system for use in a head-mounted display apparatus. The gaze-tracking system includes: at least one first optical element comprising particles of a phosphorescent or fluorescent material dispersed therein, the particles of the phosphorescent or fluorescent material being dispersed in a manner that when excited by electromagnetic radiation incident thereupon, the particles produce structured light of a given wavelength, wherein the produced structured light illuminates a user's eye; at least one camera for capturing an image of reflections of the structured light from the user's eye, wherein the image is representative of a form of the reflections and a position of the reflections on an image plane of the at least one camera; and a processor coupled in communication with the at least one camera, wherein the processor is configured to process the captured image to detect a gaze direction of the user.