The terms opening the third eye and closing the third eye aren’t technically correct.
The third eye is a natural sense we all possess. The third eye is a sense to detect “what might be” or our sense of potential. To open the third eye means to further develop that sense to the point of being aware and conscious of the sense.
Once the third eye is opened, it doesn’t come with an eyelid that we can just shut. It’s more like our ear, always on. The problem is this: some people get overwhelmed by their senses.
For example, PSTD is an excellent example of an ailment for a person overly sensitized to information their senses provides to them. Some people can be traumatized by seeing too much!
Learning how to “close the third eye” is learning how to either manage the third eye sense and how to ignore it once again.