It is much more noticeable when viewed against a field of pure blue light and is caused by white blood cells moving in the capillaries in front of the retina. White cells are larger than red blood cells and can be larger than the diameter of a capillary, so must deform to fit. As a large, deformed white blood cell goes through a capillary, a space opens up in front of it and red blood cells pile up behind. This makes the dots of light appear slightly elongated with dark tails. [4][5]
Haidingers brush is a very subtle bowtie or hourglass shaped pattern that is seen when viewing a field with a component of blue light that is plane or circularly polarized. Its easier to see if the polarisation is rotating with respect to the observers eye, although some observers can see it in the natural polarisation of sky light. If the light is all blue, it will appear as a dark shadow; if the light is full spectrum, it will appear yellow. It is due to the preferential absorption of blue polarized light by pigment molecules in the fovea. [6][7]
Purkinje images are the reflections from the anterior and posterior surfaces of the cornea and the anterior and posterior surfaces of the lens.
Although these first four reflections are not entoptic—they are seen by others who are looking at someone’s eye— Becker[8] described how light can reflect from the posterior surface of the lens and then again from the anterior surface of the cornea to focus a second image on the retina, this one much fainter and inverted. Tscherning[9] referred to this as the sixth image (the fifth image is formed by reflections from the anterior surfaces of the lens and cornea to form an image too far in front of the retina to be visible) and noted it was much fainter and best seen with a relaxed emmetropic eye. To see it, one must be in a dark room, with one eye closed; one must look straight ahead while moving a light back and forth in the field of the open eye. Then one should see the sixth Purkinje as a dimmer image moving in the opposite direction. The Purkinje tree is an image of the retinal blood vessels in ones own eye, first described by Purkyně in 1823. [10]  It can be seen by shining the beam of a small bright light through the pupil from the periphery of a subjects vision. This results in an image of the light being focused on the periphery of the retina. Light from this spot then casts shadows of the blood vessels (which lie on top of the retina) onto unadapted portions of the retina. Normally the image of the retinal blood vessels is invisible because of adaptation.