Dichroism of the macular pigment and Haidinger's brushes.

It seems quite certain that the visual entoptic phenomenon called Haidinger's brushes is a consequence of dichroism of the macular pigment; this dichroism is usually ascribed to orientation of the pigment molecules. An alternative explanation of the dichroism, an explanation that requires no orientation of pigment molecules, investigated and shown to be feasible. Specifically, it is shown that form dichroism that is due to the structure of the Henle fiber layer can account for Haidinger's brushes if the macular pigment is almost entirely confined to the Henle layer, if individual fibers have an index about 5% higher than that of the interfiber medium, and if the fibers form a tightly packed array.