Krishnamacharya on Meditative Focus

Remaining in a posture and gazing at one's favorite (ishta) icon and
experiencing a feeling of bliss is called “trataka”. It is of two
types, anta and bahi. To gaze at an outside object like an icon is
external trataka. Closing one's eyes and 'imaging' the object
internally and continually focusing attention in between the eyebrows
is the antah(r)trataka or internal gazing. One can practice this
between one to ten minutes.