An apparatus for measuring ganglion cells may include: a light generation unit configured to irradiate a first light signal polarized in a first direction and a second light signal polarized in a second direction perpendicular to the first direction to a subject; a reflected light processing unit configured to generate an amplification signal corresponding to an image of the subject using a first reflection signal, which is the first light signal reflected from the subject, and a second reflection signal, which is the second light signal reflected from the subject; and an image processing unit configured to measure ganglion cells in the subject using the amplification signal. The apparatus may be used to count the number of normal ganglion cells in the retina by measuring a phase difference of two lights polarized in different directions. The apparatus may also be used to monitor the progress of glaucoma.