SB 3.28.12

yadā manaḥ svaṁ virajaṁ
 yogena susamāhitam
kāṣṭhāṁ bhagavato dhyāyet
 sva-nāsāgrāvalokanaḥ
Synonyms: 
yadā — when; manaḥ — the mind; svam — own; virajam — purified; yogena — by yoga practice; su-samāhitam — controlled; kāṣṭhām — the plenary expansion; bhagavataḥ — of the Supreme Personality of Godhead; dhyāyet — one should meditate upon; sva-nāsā-agra — the tip of one’s nose; avalokanaḥ — looking at.
Translation: 
When the mind is perfectly purified by this practice of yoga, one should concentrate on the tip of the nose with half-closed eyes and see the form of the Supreme Personality of Godhead.
Purport: 

It is clearly mentioned here that one has to meditate upon the expansion of Viṣṇu. The word kaṣṭhām refers to Paramātmā, the expansion of the expansion of Viṣṇu. Bhagavataḥ refers to Lord Viṣṇu, the Supreme Personality of Godhead. The Supreme Godhead is Kṛṣṇa; from Him comes the first expansion, Baladeva, and from Baladeva come Saṅkarṣaṇa, Aniruddha and many other forms, followed by the puruṣa-avatāras. As mentioned in the previous verses (puruṣārcanam), this puruṣa is represented as the Paramātmā, or Supersoul. A description of the Supersoul, upon whom one must meditate, will be given in the following verses. In this verse it is clearly stated that one must meditate by fixing the vision on the tip of the nose and concentrating one’s mind on the kalā, or the plenary expansion, of Viṣṇu.