page_title: Entoptic phenomenon
section_title: Examples
hierarchical_section_title: Entoptic phenomenon / Examples
caption_attribution_description: English: Still from "Floaters" video I made.
context_page_description: Entoptic phenomena are visual effects whose source is within the eye itself.
  In Helmholtz's words: "Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. These perceptions are called entoptical."
context_section_description: Some examples of entoptical effects include:
  Floaters or muscae volitantes are slowly drifting blobs of varying size, shape, and transparency, which are particularly noticeable when viewing a bright, featureless background (such as the sky) or a point source of diffuse light very close to the eye. They are shadow images of objects floating in liquid between the retina and the jelly inside the eye (the vitreous) or in the vitreous humor itself. They are visible because they move; if they were pinned to retina by the vitreous or fixed within the vitreous they would be as invisible as ordinary viewing of any stationary object, such as the retinal blood vessels (see Purkinje tree below). Some may be individual red blood cells swollen due to osmotic pressure. Others may be chains of red blood cells stuck together; diffraction patterns can be seen around these. Others may be "coagula of the proteins of the vitreous gel, to embryonic remnants, or the condensation round the walls of Cloquet's canal" that exist in pockets of liquid within the vitreous.  The first two sort of floaters may collect over the fovea (the center of vision), and therefore be more visible, when a person is lying on his or her back looking upwards.
  Blue field entoptic phenomenon has the appearance of tiny bright dots moving rapidly along squiggly lines in the visual field. 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.
  Haidinger's 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. It's easier to see if the polarisation is rotating with respect to the observer's 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.
  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 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 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 one's own eye, first described by Purkyně in 1823.  It can be seen by shining the beam of a small bright light through the pupil from the periphery of a subject's 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. Unless the light moves, the image disappears within a second or so. If the light is moved at about 1 Hz, adaptation is defeated, and a clear image can be seen indefinitely. The v
caption: Floaters depiction
exif: {}