A system measures macular pigment of a macula of a human eye of a subject. The system comprises a light source having a first light and a second light that modulate at variable frequencies, an input device for receiving an input indicating the frequency at which the user perceives the modulation of the first light and a second light, a display device, at least one processor, and one or more memory devices. The one or more memory devices storing instructions that, when executed by at least one processor, cause the system to (i) display, on the display device, test data corresponding to the user's inputs from the input device, (ii) determine whether the test data are valid or invalid through a curve-fitting algorithm, (iii) automatically indicate that the test data are valid or invalid.