The indriyas are extremely subtle and dynamic, and independent of the outer sense organs and nervous system. Nor are the indriyas the same as the mind or the antahkarana, although the mind uses the indriyas as its implement. According to Hindu psychology, the mind is neither located in the brain, nor is it a function of the brain. The mind is independent of the brain, and is not passive. It uses the brain and the nervous system to establish contact with external objects.
Hindu psychology holds that the mind has the ability to be present all over the body.
It can also go out of the body using the external sense organs as so many doors. The mind cognizes an outer object by reaching out to that object, assuming its form, and then stimulating the indriya or indriyas to perceive that object. If an outer sense organ, for example, the organ of sight, becomes unusable due to defunct corneas, the mind will not be able to go out through that door and reach any outer object of vision. As a result, there won't be any corresponding stimulation of the indriya, nor will there be any visual perception. If the non-functioning corneas are replaced with good ones through cornea grafting, the eyes will again start functioning, as doors and visual perception will be possible.