The Compendium of Caraka 1.5.16

1.5.16

cakṣustejomayaṃ tasya viśeṣācchleṣmato bhayam/
tataḥ śleṣmaharaṃ karma hitaṃ dṛṣṭeḥ prasādanam//

The eye is made of fire; it especially has danger from phlegm; / therefore, an action that removes phlegm is beneficial as a purifier of vision.