The Ben Ish Chai, R' Yosef Hayyim of Baghdad zt”l notes that the only difference between the word "נגע" - affliction, and "ענג” - pleasure,  is that in the word "נגע”, the letter "ע" is at the end of the word, whereas in the word “ענג” the "ע" is its first letter.

     This is what is meant by the posuk "החכם עיניו בראשו" - "A wise man has his eyes ['ayin'] in his front." The meaning of this is that a wise and intelligent person places the "ayin" in front, thus changing "נגע” into “ענג” - affliction into pleasure.

     Thus, when the kohen sees that "the affliction has remained in its appearance," that the "ע" has stayed in its place and the negah has not changed into oneg, then, "he shall close him off", and the leper shall remain impure.

     This is what Dovid Hamelech writes, “הנה עין ה’ אל יראיו למיחלים לחסדו וגו” - "Behold, Hashem's eye is directed to‬‎ those who fear Him, those who anticipate His kindness" (Tehillim 33).

     The tzadikim have the ability through their prayers to move the "ayin" - and transform the negah into oneg.