punaḥ sa evāha yadyaprāpyakāri cakṣur bhavet tadā na kuṭyāder āvaraṇasyasāmarthyam astītyāvaraṇānupapattiḥ
Again, he [Uddyotakara] says: "If the eye were to operate without contact, then walls and other obstacles would have no power to obstruct [vision], thus [there would be] impossibility of obstruction."