From Jewish Spiritual Practices - 15:27:1

When you do not understand something as you study Torah it is appropriate to pray for comprehension and understanding. A hasidic story begins this way:

The holy Rabbi Aaron of Karlin of blessed memory was once studying the Gemara (Talmud) and he had a difficult time understanding a certain matter. This made him so unhappy that he started to become depressed. So he turned to G-d in prayer and prayed mentally to Him, blessed be He, that He lighten his eyes. Then he applied himself in total concentration to try again to understand. (Zichron L'Rishonim p. 27)

Note how this practice leads us to a devotional attitude to Torah. It keeps us from pride over our Torah knowledge and makes us realize that our ability to understand, our intelligence and wisdon, comes from G-d.