To be published in "Natural and Technical Sciences"
(Estestvennye i Tekhnicheskie Nauki, ISSN 1684-2626)
2006, Iss.5, in Russian.
Translation by author
On hominoid eyes shine
Numerous encounters with hominoids show that they are remarkably active in twilight and through nights. They confidently move in dark forests and in other cases in darkness that is very inconvenient for a human. Such ability allows to postulate that hominoids have developed some means by which they increase sensitivity of their seeing in darkness of nights.
There are many kinds of nocturnal animals. Investigations of their eyes reveal various means of adaptation to dark conditions. They include increase of eye size and abilities to significant widening of pupils that increase light stream on photosensitive elements in eye. Some animals, for example, feline and canine families have developed some other abilities that improve vision in dark. It is known to all, that at nights the eyes of dogs and cats intensively reflect head-lights like to small mirrors.
In retina of eyes of these animals under a layer of photosensitive cells there is a layer of the cells that reflect light ¾ the tapetum lucidum. Improvement of vision in dark in this case is achieved as photons of light, which missed photosensitive pigments of retina and had not participated in photochemical reactions, after reflection again cross a photosensitive layer in the opposite direction and have additional probability to react with these pigments. Thus, the reflection of light in an eye makes effect that is almost equivalent to double external light (almost is due to absorption of photons at the first passage of light and losses at reflection, i.e. the reflected stream is always less intensive than initial). These means of adaptation to dark are well studied and confirmed by observations on alive animals, as well by morphological investigations.
When we speaking about hominoid abilities to dark vision, we yet can judge the phenomenon according to words of eyewitnesses only. There are many observations of hominoids which point out that their eyes have some specific features and which are not found in other animals.
I show here some examples from reports of eyewitnesses:
*** "At once two Kuls stepped up from woods. One of them was higher than 2 meters, and the second was lower. I was frightened too, because the their eyes showed light like two dark red lantern. They went close by me and suddenly had looked at me with sparkled eyes. They had no clothes at all and their bodies were covered by short dense hair." Western Siberia, V.Pushkarev's record, 1978 
*** "I saw that a figure like human stayed in front of me. It was silent. I was not frightened because I was convinced he was a man. Then I saw that its eyes flash with red light, changing from dim to bright and again to dim." Northern Caucasus, record by J.-M.Kofman, 1964, unpublished.
*** "It was about 12-years boy high, humpbacked. Its hands were longer than human and low down to knees, or even lower. Its legs were clumsy. Its eyes shone brightly like red lanterns." Northern Caucasus, record by D.Bayanov, 1964, unpublished.
*** Craig Heinselman in article “Eye Shine, Why and How”, 1999  said that Bigfoot of America also demonstrate this phenomenon. Descriptions of Bigfoot shining eyes observed at encounters are posted in many Web sites of American researchers.
Similar observations accomplish rather authentic depiction of the phenomenon. Their most important feature is that the shining of hominoid eyes in no way can be connected with mirror effect, as during these observations there were no sources of external light which could be reflected by their eyes.
So, it is natural to postulate that the luminescence of hominoid eyes is connected by some means with their abilities to night vision. Thus, the conclusion arises that hominoids have new means for enhanced night vision which are unknown to science yet. The internal red luminescence in its eye is seen from outside through pupils as shine.
Let us consider, whether any physical base for such hypothesis exists.
A photon of light, absorbed by photosensitive pigment in retina of eye, causes in it a photochemical reaction. In human eye it may be, for example, transformations of rhodopsin in rods for night vision and some other pigments in cones for daylight color vision. Electric potentials arising at these reactions are transmitted by nerves to parts of brain, which recreates from such signals a visible picture of the world around. The more intensive the stream of photons (light is brighter), the more products of reaction are developed, nervous impulses are stronger and the visible picture (certainly, within limits of the pigments) is more precise.
Quantum aspects play the most important role in consideration of photochemical reactions. The quantities of products in such reactions are results of probability characteristics depending on photon states and energy levels of molecule and different functional groups in it. For ground and excited states of a molecule the output of a reaction can be essentially different. For biomolecules due to their complexity these distinctions can be especially great.
Electromagnetic irradiation in general and by visible light in particular is one of methods of molecule exciting. For this process energy of light quantum (corresponding with the length of wave) should not lead to destruction of the molecule, but to excitation only.
To applying these considerations to the phenomenon of hominoid eyes luminescence in dark environment, it is possible to state the following hypothesis about the mechanism of their dark adaptation.
In retina of hominoid eye besides cells, common to vertebrate animals and well studied, there are other elements capable to intensive red luminescence. Energy of photons of this radiation is lesser than in other visible light range (the wave length is the greatest). This dimmed inner radiation excites pigments in photochemical receptors to upper energy levels, and they become essentially more sensitive to external light of low density in other visible range. Hominoids get their dark vision considerably improved. Part of red radiation produced by the luminescence leaves eye through its pupil and becomes visible to various spectators. The intraocular luminescence is controlled by nerve center in the same way as widening of pupil, involuntarily, depending on conditions of environment. When light is bright enough the red eye illumination is absent.
For better understanding of the hypothesis a search of relevant information in scientific data bases was fulfilled. Despite of wide researches of human eye, made during last years, no published experimental works with human eyes, as nearest to hominoids probably, were found. Apparently, researchers had no reasons for such investigations. However, the experimental work made by F.J.Luo and P.H.Liang  on isolated carp retina gave some hints in favor of the proposed hypothesis. Authors  had showed, that dim red irradiation of the retina light receptors made higher their response to green light. As, by the way, dimmed green light improved response to red. As eyes of all vertebrates have in basic a similar structure, it is possible to expect, that photosensitive pigments in human eye (and in hominoid eyes also) would give similar response in similar states.
Now let us pay attention to the second side of the phenomenon ¾ what elements in hominoid eye are capable to generate dimmed red light. Till neither hominoids, nor their bodies or parts of them are in hands of researchers, some conclusions could be made on analogues with results in human eye investigations. And in this field, despite of remarkable success, there are unclear problems ¾ see the fundamental review , in which reactions of various pigments in eye on light and in dark are considered. The eye of vertebrate appears much more complex and multifunctional body, than it was seemed until recently. But luminescence elements, as far as it is known up to now, are not found out in human eye yet.
However, the effect of shining eyes is observed occasionally among humans also. I here shall not go into its explanations, or to argue, whether it is atavism or a unique product of a developed brain. Practically nothing is written about it, and the very existence of the fact in a case, when someone has such abilities, carefully conceals. The reason of such behavior, in my opinion, is usual steady prejudice. I know about this phenomenon not by rumor ¾ there is a girl among my relatives, now she is a young woman, who possesses such abilities.
For the first time it had been noticed under such circumstances. Once, when she was about three, mum had put her to bed.. Parents slept beside in a nearby room. At midnight mum has woken up because of some noise in the nursery. She entered there and saw that the daughter played with her toys on floor almost in full darkness. Her eyes shined by red-orange light. It was obvious that she perfectly saw her toys to play. Later she repeatedly demonstrated this ability. During late evening walks or at home in twilight her eyes usually were without peculiarities, but if something new interesting for her appeared and she would like to consider it with curiosity, her eyes began to shine for the time of interest. In following years such cases became seldom ¾ apparently, unfamiliar objects became rare for her in around environment, though they occurred occasionally now too. It is a remarkable feature of this ability ¾ she can not make her eyes to shine deliberately.
I think, that really such abilities are not so rare among peoples. Otherwise how steady language expressions (at least in Russian) would appear in such context: "He has seen the treasure, and his eyes lighted up". Apparently, such messages should be often understood not metaphorically, but literally. Especially, if event was occurred in darkness. As to hominoids, they, naturally, much more time are in rough positions of aggression or protection, intensive studying of environment, and mainly nocturnal life. So, shining eyes of hominoids are noticed at higher share of encounters.
Until the phenomenon is not acknowledged as existing, there are also no investigations to reveal eye structures that produce it. From the told above it is obvious, that the experimental research of luminescence in human eye can be very complicated. owing to not clear The mechanism of possible activation of this process is not clear at all and, apparently, may be impossible on isolated retina.
1. Pushkarev Vladimir. The new observations. "Technika - molodezhi", ¹6, 1978, page 48-52 (In Russian, translation by M.Trachtengerts in http://www.alamas.ru/eng/publicat/Pushkarev_e.htm)
2. Heinselman Craig, Eye Shine, Why and How, 1999, see athttp://www.bigfootencounters.com/biology/eyeshine.htm
3. Luo F.J., Liang P.H. Metabotropic glutamate receptor-mediated hetero-synaptic interaction of red- and green-cone inputs to LHC of carp retina. Brain Res. Bull., 2003, v. 60, iss. 1-2, pp.67-71.
4. Gordon L. Fain et al. Adaptation in Vertebrate Photoreceptors, Physiological Reviews, 2001, v.81,¹1, pp. 117-151