This microscope picture shows a small yellow bump on the lower eyelid. This is an epithelial inclusion cyst and it is yellow because it is filled with yellow keratin material. The vertical line is a line of light that the doctor uses to get a better idea of size and depth.

This can be easily lanced and the inner keratin removed by an eye doctor at the slitlamp. To get a better idea how this looks, you may want to watch the yellow inclusion bump video from which this snapshot was captured.