http://www.chan1.org/ddp/channews/10-1987.htmlThe Buddha explains to Ananda that beings on different levels, although they may look at the same thing, will really see it according to their own perspective. The Buddha then continues to talk about different levels of vision. The Buddha sees all things as equal, undifferentiated, but he can also see things as ordinary beings see them. The Buddha explains how things are perceived from five different levels. They are:
The eye of ordinary sentient beings
The heavenly eye
The eye of an arhat
The eye of a bodhisattva
The eye of the Buddha
------------------------------
The article is too long, so I've only pasted a small summary of it. The eye of ordinary sentient beings is what we all have. The heavenly eye is the eye being able to view greater distance and the sight penetrate into the supernatural world. The Buddha's eye is that with immense wisdom, able to see through the nature of reality across the universe and beyond - the nature of emptiness. Please do read the article, it may answer your question.
Some people are born with a "third eye", does that mean that they have a
deva eye?
Usually these people have spiritual eyes, but not necessary deva eyes. There are limitations, and Venerable Sheng-yen has mentioned about his encounter with people having "spiritual eyes":
Have you ever seen a ghost or a god? Normally people can't see things that are too far, near, big, or small. But some people borrow the power of a ghost or other spiritual being, and gain spiritual vision. There are also cases of heavenly beings who are born into the human realm, who still retain some ability to see ghosts and spirits in the realms below. They can no longer see into the heavenly realm, nor can they see ghosts and spirits in the human realm.
I had a student who came here for a beginner's class. She claimed to have some psychic power. She said that when she was well-concentrated, she could see into people's past, but I had my doubts. I asked her if she could see into my past. I have heavy karmic obstructions, which have their root in past lives, but still she could see nothing of my past. Why? People are not always reborn into the human realm. They might be born into a distant world, and ordinary psychic power would be too limited to see that far. It would be similar to a person who commits a crime in Taiwan and moves to New York. The New York police would have no record of the crime.
The ghostly or deva eye stands at a level between the fleshy and heavenly eyes. This phenomenon occurs when a spiritual being uses the eye of a human being as a medium. People who have experienced this believe that they have been endowed with great spiritual powers, but it is really the power of the spiritual being at work. There is a book about a spirit called Seth who used a woman's body to talk to people in this world. He could only talk through her.The whole article is very interesting, I've only pasted part of it.
but then they are people who are born with clincial depression...
Certain mental illnesses, like amnesia, or even insanity, I classify them as "Karmic Obstruction Diseases". These people have commited some bad karma in previous life and have to suffer from certain mental disorders.
However, I believe clinical depression can be treated - but Medicine is usually not enough. Medicine can decrease the depression symptoms by causing chemical reactions in the brain, however, if he does not treat the root cause of samsara, depressing thoughts are sure to arise after the medicine has worn off.
If a friend of yours have depression, you can ask him to go for a meditation course, it can calm his mind. Ask him to go to a dharma centre to learn about Buddhadharma, and to apply it in everyday life. There'll surely be positive effects.