People often call eyes the windows to the soul. But what exactly do we see when we gaze into the eyes of another person? In fact, the eyes do provide lots of information about another person’s emotional state.

When people are sad or worried, they furrow their brow, which makes the eyes look smaller. Yet when people are cheerful, we correctly call them “bright-eyed.” That’s because people raise their eyebrows when they’re happy, making the eyes look bigger and brighter.

We can tell a true  smile from a fake by looking at a person's eyes. The mouth shape of a smile is easy to fake—we do it all the time out of politeness. But the eyes are the giveaway: When we’re truly happy, we not only smile but also crinkle the corners of our eyes in a “crow’s feet” pattern. But when people fake a smile, they usually forget about their eyes.

If the eye is the window into the soul, the pupil is—quite literally—an opening into the eye. The pupil acts like the aperture on a camera, dilating or contracting to regulate the amount of light coming into the eye. We all know that our pupils get smaller in the light and bigger in the dark. This is the pupillary light response.

In an article published in a recent issue of Current Directions in Psychological Science, psychologists Sebastiaan Mathôt and Stefan Van der Stigchel argue that there’s a lot more to the pupillary light response than, well, meets the eye. They claim that the size of the pupils tells us a lot about the emotions and intentions of their owners.

According to the researchers, the pupillary light response isn’t just a mechanical reaction to ambient light. Rather, as we shift our gaze from one spot to another, our pupils adjust their size in advance to the amount of light we expect to encounter at the new location.

Consider working at a computer: Most of the time, our gaze is fixed on the bright screen, so our pupils are contracted. But every now and then, we glance down at the keyboard, as when we need to reposition our fingers. The authors of the article claim that the pupils begin to dilate even before the downward eye movement begins. Because the pupillary light response is relatively slow—about a quarter of a second—anticipating the amount of light at the new location improves vision once our gaze gets there. (All of this, of course, operates below the level of consciousness.)

The pupillary light response is only one reason why the pupils change size. They also dilate when we’re aroused. The body has an alarm network called the autonomic nervous system that prepares us to take action whenever we detect a threat—or an opportunity—in our environment.

Encounter a bear while walking through the woods, and your autonomic nervous system goes on alert. Your heart and breath rates increase, you begin to sweat as your muscles tense up, and, among other bodily reactions, your pupils dilate. The autonomic nervous system prepares your body to take action against the threat—perhaps scampering up the nearest tree.

In Dharmic spiritual traditions from India, the third eye refers to the ajna (or brow) chakra. The third eye refers to the gate that leads to inner realms and spaces of higher consciousness. In New Age spirituality, the third eye often symbolizes a state of enlightenment or the evocation of mental images having deeply personal spiritual or psychological significance. The third eye is often associated with religious visions, clairvoyance, the ability to observe chakras and auras, precognition, and out-of-body experiences. People who are claimed to have the capacity to utilize their third eyes are sometimes known as seers. In Hinduism and Buddhism, the third eye is said to be located around the middle of the forehead, slightly above the junction of the eyebrows, representing the enlightenment one achieves through meditation. Hindus also place a "tilaka" between the eyebrows as a representation of the third eye, which is also seen on expressions of Shiva .Buddhists regard the third eye as the "eye of consciousness," representing the vantage point from which enlightenment beyond one's physical sight is achieved.

In Taoism and many traditional Chinese religious sects such as Chan (called Zen in Japanese), "third eye training" involves focusing attention on the point between the eyebrows with the eyes closed, and while the body is in various qigong postures. The goal of this training is to allow students to tune into the correct "vibration" of the universe and gain a solid foundation on which to reach more advanced meditation levels. Taoism teaches that the third eye, also called the mind's eye, is situated between the two physical eyes, and expands up to the middle of the forehead when opened. Taoism claims that the third eye is one of the main energy centers of the body located at the sixth Chakra, forming a part of the main meridian, the line separating left and right hemispheres of the body. In Taoist alchemical traditions, the third eye is the frontal part of the "Upper Dan Tien" (upper cinnabar field) and is given the evocative name "muddy pellet".

According to the Christian teaching of Father Richard Rohr, the concept of the third eye is a metaphor for non-dualistic thinking; the way the mystics see. In Rohr's concept, mystics employ the first eye (sensory input such as sight) and the second eye (the eye of reason, meditation, and reflection), "but they know not to confuse knowledge with depth, or mere correct information with the transformation of consciousness itself. The mystical gaze builds upon the first two eyes—and yet goes further." Rohr refers to this level of awareness as "having the mind of Christ".

Adherents of theosophist H.P. Blavatsky have suggested that the third eye is in fact the partially dormant pineal gland, which resides between the two hemispheres of the brain.Reptiles and amphibians sense light via a third parietal eye—a structure associated with the pineal gland—which serves to regulate their circadian rhythms, and for navigation, as it can sense the polarization of light. C.W. Leadbeater claimed that by extending an "etheric tube" from the third eye, it is possible to develop microscopic and telescopic vision. It has been asserted by Stephen Phillips that the third eye's microscopic vision is capable of observing objects as small as quarks. According to this belief, humans had in far ancient times an actual third eye in the back of the head with a physical and spiritual function. Over time, as humans evolved, this eye atrophied and sunk into what today is known as the pineal gland. Dr. Rick Strassman has hypothesized that the pineal gland, which maintains light sensitivity, is responsible for the production and release of DMT(dimethyltryptamine), an entheogen which he believes possibly could be excreted in large quantities at the moments of birth and death.