A method for quantifying pigment position in retinal pigment epithelium.

In wildtype mice, the pigment granules in the retinal pigment epithelium aggregate in the dark towards Bruch's membrane and disperse towards the photoreceptors in the light. We have developed a repeatable method amenable for quantifying pigment position in the RPE from wild type mice by estimating the population density of pigment granules, or pigment density, within 4 μm areas in the basal part of cells examined by transmission electron microscopy. To measure pigment position, 2 μm × 2 μm squares were aligned along the apical ends of the basal microvilli.