An apparatus (200, 500) comprising: - an imaging unit configured to acquire an image of an eye, - a substantially planar waveguiding substrate, - a light source configured to provide a first light beam, said first light beam being substantially collimated, - an in-coupling grating configured to diffract light of said light beam into said substrate and to form a first in-coupled beam and a second in-coupled beam propagating in different directions within said substrate, - a first expanding grating portion configured to provide a first expanded internal beam by diffracting light of said first in-coupled beam, - a second expanding grating portion configured to provide a second expanded internal beam by diffracting light of said second in-coupled beam, - a first out-coupling grating portion configured to form a first substantially collimated illuminating beam by diffracting light of said first expanded internal beam out of said substrate, - a second out-coupling grating portion configured to form a second substantially collimated illuminating beam by diffracting light of said second expanded internal beam out of said substrate, said illuminating beams (B11, B12) having different directions such that said first illuminating beam provides a first reflection spot when light is reflected from the surface of the eye and that said second illuminating beam provides a second reflection spot when light is reflected from the surface of said eye, said reflection spots appearing in said image, and - a data processing unit configured to determine the gaze direction of the eye with respect to said apparatus (200, 500) based on the position of said first reflection spot in said image, on the position of said second reflection spot in said image, on the position of the pupil and/or iris of the eye in said image and on the directions of the illuminating light beams (B11, B12). - an imaging unit configured to acquire an image of an eye, - a substantially planar waveguiding substrate, - a light source configured to provide a first light beam, said first light beam being substantially collimated, - an in-coupling grating configured to diffract light of said light beam into said substrate and to form a first in-coupled beam and a second in-coupled beam propagating in different directions within said substrate, - a first expanding grating portion configured to provide a first expanded internal beam by diffracting light of said first in-coupled beam, - a second expanding grating portion configured to provide a second expanded internal beam by diffracting light of said second in-coupled beam, - a first out-coupling grating portion configured to form a first substantially collimated illuminating beam by diffracting light of said first expanded internal beam out of said substrate, - a second out-coupling grating portion configured to form a second substantially collimated illuminating beam by diffracting light of said second expanded internal beam out of said substrate, said illuminating beams (B11, B12) having different directions such that said first illuminating beam provides a first reflection spot when light is reflected from the surface of the eye and that said second illuminating beam provides a second reflection spot when light is reflected from the surface of said eye, said reflection spots appearing in said image, and - a data processing unit configured to determine the gaze direction of the eye with respect to said apparatus (200, 500) based on the position of said first reflection spot in said image, on the position of said second reflection spot in said image, on the position of the pupil and/or iris of the eye in said image and on the directions of the illuminating light beams (B11, B12).