A gaze-tracking system for use in a head-mounted display apparatus, the gaze-tracking system comprising: - a first light source, the first light source being operable to emit light of a first type, the light of the first type is light polarized at a first polarization orientation, wherein the light of the first type is to be directed towards a user's eye when the head-mounted display apparatus is worn by the user; - a second light source, the second light source being operable to emit light of a second type, wherein the light of the second type is to be used to diffusely illuminate the user's eye when the head-mounted display apparatus is worn by the user; - an image sensor, the image sensor being operable to capture an image of the user's eye and reflections of the light of the first type from the user's eye, wherein the reflections of the light of the first type appear as at least one glint in the captured image, while the light of the second type enables pupil detection in the captured image, an optical path of the light of the first type, which corresponds to an optical path between the first light source and the image sensor, via the user's eye, being longer than an optical path of the light of the second type, which corresponds to an optical path from the user's eye to the image sensor; - a primary lens associated with the image sensor; - an aperture device (200, 310), the aperture device (200, 310) being positioned between the image sensor and the primary lens, wherein the aperture device (200, 310) provides a first aperture to the light of the first type and a second aperture to the light of the second type; and - a processor coupled in communication with the first light source, the second light source and the image sensor, the processor being configured to control the first light source, the second light source and the image sensor, and to process the captured image to detect a gaze direction of the user, characterised in that the first aperture and the second aperture are substantially concentric, the first aperture being smaller than the second aperture, wherein the aperture device (200, 310) comprises a first portion and a second portion that are substantially concentric with each other, wherein the first portion acts as the first aperture, while the first portion and the second portion together act as the second aperture, further wherein the first portion is a polarizer that does not block the light polarized at the first polarization orientation and allows the reflections of the light of the second type to pass therethrough, and the second portion is implemented by way of a polarizer that is to be aligned to block the light polarized at the first polarization orientation. - a first light source, the first light source being operable to emit light of a first type, the light of the first type is light polarized at a first polarization orientation, wherein the light of the first type is to be directed towards a user's eye when the head-mounted display apparatus is worn by the user; - a second light source, the second light source being operable to emit light of a second type, wherein the light of the second type is to be used to diffusely illuminate the user's eye when the head-mounted display apparatus is worn by the user; - an image sensor, the image sensor being operable to capture an image of the user's eye and reflections of the light of the first type from the user's eye, wherein the reflections of the light of the first type appear as at least one glint in the captured image, while the light of the second type enables pupil detection in the captured image, an optical path of the light of the first type, which corresponds to an optical path between the first light source and the image sensor, via the user's eye, being longer than an optical path of the light of the second type, which corresponds to an optical path from the user's eye to the image sensor; - a primary lens associated with the image sensor; - an aperture device (200, 310), the aperture device (200, 310) being positioned between the image sensor and the primary lens, wherein the aperture device (200, 310) provides a first aperture to the light of the first type and a second aperture to the light of the second type; and - a processor coupled in communication with the first light source, the second light source and the image sensor, the processor being configured to control the first light source, the second light source and the image sensor, and to process the captured image to detect a gaze direction of the user, characterised in that the first aperture and the second aperture are substantially concentric, the first aperture being smaller than the second aperture, wherein the aperture device (200, 310) comprises a first portion and a second portion that are substantially concentric with each other, wherein the first portion acts as the first aperture, while the first portion and the second portion together act as the second aperture, further wherein the first portion is a polarizer that does not block the light polarized at the first polarization orientation and allows the reflections of the light of the second type to pass therethrough, and the second portion is implemented by way of a polarizer that is to be aligned to block the light polarized at the first polarization orientation.