गोविन्द भाष्य (श्रील बलदेव विद्याभूषण - अचिन्त्यभेदाभेद वेदान्त ब्रह्मसूत्र भाष्य सटीक)

antaraḥ—the person within; upapatteḥ—because of reason.
The person in (the eye is the Supreme Personality of Godhead) because (that
conclusion is dictated) by reason.
Purport by Śrīla Baladeva Vidyābhūṣaṇa
The person in the eye is the Supreme Personality of Godhead. Why? The sūtra
says upapatteḥ (because that conclusion is dictated by reason). This is so because
of the proof given (in the quote from the Chāndogya Upaniṣad) in the description
of the qualities beginning with being the Supreme Self(ātmā), immortality (amṛta),
being the greatest (brahma), being untouched by material things, and being the
abode of all opulences (sampad-dhāma). (These qualities can properly be attributed
only to the Supreme Personality of Godhead.)
Sūtra 14
sthānādi-vyapadeśāc ca
sthāna—the place; ādi—beginning with; vyapadeśāt—because of the statement.
ca—also.
And also because of the teaching (in the scriptures that the Supreme
Personality of Godhead is present) in this place and in other places as well.
Purport by Śrīla Baladeva Vidyābhūṣaṇa
That the Supreme Personality of Godhead is the controller who resides with the
eye is described in Bṛhad-āraṇyaka Upaniṣad (3.7.18):
yaś cakṣuṣi tiṣṭhaṁś cakṣuṣo 'ntaro yaṁ cakṣur na veda yasya cakṣur śarīraṁ yaś
cakṣur antaro yam ayaty eṣa ta ātmāntaryāmy amṛtaḥ
"He who stays in the eye, who is within, whom the eye does not know, who is
the ultimate proprietor of the eye and the body, and who, residing within, controls
the eye, is the immortal Supersoul, the Supreme Personality of Godhead who
resides in the heart."