The parsha tells us that Yitzchak could not see who he was giving a bracha to because “va’tichena einav mei’re’os,” his eyes were dim and he could not see. Seforno points out that Avraham and Ya’akov did not suffer the same loss of vitality in old age, but we find that Eli haKohen grew blind because he did not admonish his children properly. Seforno seems to be suggesting that Yitzchak had too soft a hand in dealing with Eisav and therefore suffered blindness as a punishment -- interesting that he would attribute guilt to Yitzchak where, as far as I know, Chazal do not. Netziv suggests that Yitzchak’s blindness was b’hashgacha so that Ya’akov would be able to take the brachos meant for Eisav. Similarly, the Midrash suggests that the blindness was not a punishment, but was for Yitzchak’s benefit. The word “mei’re’os” in the pasuk is extra – obviously someone with dim vision cannot see. The Midrash darshens that the pasuk is alluding to the reason for Yitzchak’s blindness: so that he would not be able to see and be disappointed by the bad deeds of Eisav. According to another view Yitzchak’s blindness prevented him from going out of his home – from being seen in public – sparing him the embarrassment of hearing people remark that this was the father of that rasha Eisav. (I guess it’s human nature for that people remark on his being the father of Eisav the rasha while ignoring the fact that he was also the father of Ya’akov the tzadik. It's much more fun to focus on the negative.)
Assuming that Yitzchak’s blindness is not a punishment for any wrongdoing on his part, then I think we have to assume the benefit of his not being the subject of public gossip or the benefit of his not seeing Eisav doing wrong outweighed the cost of his suffering blindness. Sometimes bad things happen and the reason why is because they are better than the alternative, which the person suffering may not even imagine. What bothers me is that Chazal tell us “suma chashuv k’meis,” blindness is equivalent to death. Is being the focus of gossip or feeling bad because your kid is OTD a fate worse than death? How can anything outweigh death in the cost/benefit analysis?
Let me suggest an answer (and I hope someone has a better one). When Chazal equate being blind with death, it is metaphorical. Built in to the nature of a Jew is the desire to show chessed and rachmanus. What Chazal are telling us (as R’ Eliezer Eisenberg summarizes from R’ Chaim Shmuelevitz here) is that when a person is blind and cannot see the pain of others and cannot react and respond, he has lost something of his humanity. It’s much harder to do chessed under those circumstances, and without the ability to do chessed, something essential is lacking from life. Perhaps what the Midrash means is that when you have to deal with an Eisav ha’rasha, showing rachmanus may make things worse (see the Seforno above). When people you are the subject of gossip in the street, maybe it’s not worth going out and doing chessed for those people. The eyes are a kli for doing kindness. The removal of Yitzchak’s sight so he would not have to see Eisav, or not have to go out and be exposed to slander, is a “ptur,” so to speak, granted by Hashem, so that Yitzchak would not be able to or required to extend chessed to those who were not deserving of it.