I have a doubt about spiritual eye.
The spiritual eye really appears between the eyebrows (obviously It depends on the spiritual development) or is it imagined (visualization) and due to great concentration during meditation it appears in our mind?
The spiritual eye is very real and definitely does appear, sooner or later, to everyone who sincerely meditates.
For some people it takes a while, maybe many years. For some, it is immediate; and for others, it appears once or twice in the beginning and then is not seen again for a long time after that.
Some meditators are more tuned into hearing sounds (like the sound of AUM) than seeing light (the spiritual eye), or having feelings of energy rising in the spine. We are all different, and we are at different places in our spiritual evolution.
Just because a person does not see the spiritual eye does not mean that the person is not making spiritual progress!
An attitude of never giving up and the courage to be willing to go on meditating forever, no matter what — this is what is truly important!
However, with that said, it does help to visualize or imagine the spiritual eye at the point between the eyebrows when you are meditating. This is the place where you need to keep your attention anyway, whether you "see" anything or not.
Sometimes there will be a dim or bright light or moving light patterns which will appear behind closed eyes, even if very briefly. Eventually, as the mind and breath becomes very calm, these lights will form themselves into the true appearance of the spiritual eye, which is very beautiful: a halo of golden light, surrounding a deep blue-violet tunnel at the center of which is a tiny, silver-white, five-pointed star.
Concentration in meditation is very important, but concentration alone does not, in itself, bring on the appearance of the spiritual eye. Many other factors are involved: devotion, grace, perseverance, relaxation, joyful expectation, self-offering, help from and faith in God and Guru, as well as always praying for guidance in meditation and non-attachment to results, to name a few.