John Chrysostom

"And immediately there fell from his eyes as it had been scales." Some say this was a sign of his blindness. Why did he not blind his eyes entirely? This was more wonderful, that, with his eyes open, he did not see: which was just his case in respect of the Law, until the Name of Jesus was put on him. With hands laid on, he spake these words. "And immediately there fell from his eyes," etc.: a double blindness is removed.

Homily on Acts 20 ↗

Theophylact of Ohrid

"And immediately something like scales fell from his eyes." The scales fall off and show that the inflammation was severe and that the healing is beyond doubt.

Commentary on Acts ↗

Oecumenius

Scales fell away, showing the sharpness of the blindness, and the undeniability of the healing.

Commentary on Acts ↗

Bede

And immediately something like scales fell from his eyes. It is said that the entire body of the dragon is covered with scales. Because the Jews are called serpents and brood of vipers, those who followed their perfidy had covered the eyes of their heart as if with the skin of a serpent. But when the scales fell from his eyes under the hand of Ananias, it was shown in his face that he had already received true light in his mind.

Commentary on Acts ↗