Developed to provide a quick, easy, accurate and repeatable test, the MapcatSF measures macular pigment optical density (MPOD), as well as other novel parameters, to provide essential information about the patient’s eye. The MapcatSF measures:
Macular Pigment Optical Density
Lens Optical Density
Lens Equivalent Age
Percentage of blue light blocking by macular pigment
Because Macular Pigment (MP) strongly absorbs light in the range of 455-460nm, this can be used to measure MPOD by flickering alternating blue and green stimuli for the patient to see (blue light is strongly absorbed by MP before reaching the photoreceptors, green light passes through unchanged).
Using a technique called customized Heterochromatic Flicker Photometry (cHFP), the MapcatSF is a psychophysical response test, where the patient turns a control dial in order to find the point where the stimulus stops flickering (the ‘flicker null point’). It tests first at the fovea, then in the perifoveal area.
The reason for the two-part test is to eliminate the contribution of lens yellowing. The blue intensity required for the null point in the central test will depend on absorption by both the macular pigment and lens, whereas for the perifoveal test, only the lens will be the significant absorber. By a subtraction process, the lens can be eliminated leaving only the contribution by the macular pigment.
Traditional HFP used a small eccentric fixation target, with subjects being asked to fixate while perceiving the flickering stimulus in the periphery of their vision. There is a tendency for the subject to look towards the stimulus during this part of the test, thereby negating the result.
The MapcatSF overcomes this problem by utilizing a large, 15 degree stimulus for the perifoveal component. The subject is required to fixate on a crosshair in the center of the stimulus, and the null point is achieved when there is a perception of the flickering ceasing around the periphery of the stimulus.