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.
[11]
A phosphene is the perception of light without light actually entering the eye, for instance caused by pressure applied to the closed eyes.A phenomenon that could be entoptical if the eyelashes are considered to be part of the eye is seeing light diffracted through the eyelashes. The phenomenon appears as one or more light disks crossed by dark blurry lines (the shadows of the lashes), each having fringes of spectral colour. The disk shape is given by the circular aperture of the pupil. See also
References
Sources
Jan E. Purkyně, 1823: Beiträge zur Kenntniss des Sehens in subjectiver Hinsicht in Beobachtungen und Versuche zur Physiologie der Sinne, In Commission der J.G. Calveschen Buchhandlung, Prag. H. von Helmholtz, Handbuch der Physiologischen Optik, published as "Helmholtzs Treatise on Physiological Optics, Translated from the Third German Edition," ed. James P. C. Southall; 1925; The Optical Society of America. Leonard Zusne, 1990: Anomalistic Psychology: A Study of Magical Thinking; Lea; ISBN 0-8058-0508-7 [12]
Becker, O., 1860, “Über Wahrnehmung eines Reflexbildes im eigenen Auge [About perception of a reflected image in your own eye],” Wiener Medizinische Wochenschrift, pp. 670 672 & 684 688. M. Tscherning, 1920, Physiologic Optics; Third Edition, (English translation by C. Weiland). Philadelphia: Keystone Publishing Co. pp. 55–56. White, Harvey E., and Levatin, Paul, 1962, "Floaters in the eye," Scientific American, Vol. 206, No. 6, June, 1962, pp. 199 127. Duke Elder, W. S. (ed. ), 1962, System of Ophthalmology, Volume 7, The Foundations of Ophthalmology: heredity pathology diagnosis and therapeutics, St. Louis, The C.V. Mosby Company. p450.