There are inward requirements for this kind of special fasting carried out by the righteous.
It means keeping one's organs, free from sin, and some points are required for its accomplishments.
The first point is, see not what displeases Allah. In other words, a chaste regard, restrained from viewing anything that is blame worthy, and diverts the heart from the remembrance of Allah.
The Prophet once said that the furtive glance, is one of the poison arrows of Shaitan, and whoever forsakes it, for the sake of the fear of Allah, will receive from him, a faith.
The sweetness, of which he will find in his heart.
Watch the full teaching by the Prophet's Path in this video.