7 But rather, I should say, what language is fully adequate to set forth the whole excellency of this member? And why do I speak of the pupil and the visual faculty? For if you were to investigate that which seems the meanest of all the members, I mean the eyelashes, you would behold even in these the manifold wisdom of God the Creator! For as it is with respect to the ears of grain; the beards, standing forth as a sort of spears, repel the birds, and do not suffer them to settle upon the fruits, and to break the stalk, which is too tender to bear them; so also is it with regard to the eyes.
The hairs of the eyelids are ranged in front, and answer the purpose of beards and spears; keeping dust and light substances at a distance from the eyes, and any thing that might incommode the sight; and not permitting the eyelids to be annoyed. Another instance of wisdom, no less remarkable, is to be observed in eyebrows. Who can help being struck by their position? For they do not project to an immoderate degree, so as to obscure the sight; nor do they retire farther back than is fitting; but in the same manner as the eaves of a house, they stand out above, receiving the perspiration as it descends from the forehead, and not permitting it to annoy the eyes.
For this purpose too there is a growth of hair upon them, which serves by its roughness to stay what descends from above, and affords the exact protection that is needed, and contributes also much appearance of beauty to the eyes. Nor is this the only matter of wonder! There is another thing also which is equally so. How is it, I ask, that the hairs of the head increase, and are cut off; but those of the eyebrows, not so? For not even this has happened undesignedly, or by chance, but in order that they might not darken the sight too much by becoming very long; an inconvenience from which those suffer who have arrived at extreme old age.
Source: Homilies on the Statues (New Advent)