I once heard that Yitzhak got blind (Genesis 27:1) because G-d showed him the whole world, the future, etc. (basically G-d's view). But I've also heard one opinion that says that he got blind because of the tears of the angels in his sacrifice. What's the most common reason of the cause of his blindness? What are the bases of these reasons?
Rashi on Genesis 27:1:1:
ותכהין. בעשנן של אלו דבר אחר כשנעקד על גבי המזבח והיה אביו רוצה לשחטו, באותה שעה נפתחו השמים וראו מלאכי השרת והיו בוכים וירדו דמעותיהם ונפלו על עיניו, לפיכך כהו עיניו. דבר אחר כדי שיטול יעקב את הברכות:
Synopsis of ideas mentioned - Either he was blinded from the smoke of his own sacrifice (when he was offered as one), or, as you stated, that the skies opened up and the tears form the angels fell into his eyes and blinded him.
Rashba"m on the above verse gives a simple answer - from aging. (Ever hear of macular degeneration? I guess that same idea existed then, but without the medical name.)
Kitzur Ba'al Haturim doesn't give a direct cause, but rather a reason / benefit - because he was bribed by Esav, and it says (in Devarim) that bribes blinds righteous people.
Tanchuma says that he was blinded from the smoke of the avodah zarah from Esav's wives.
I've listed a few explanations. You can see a few others via the sidebar on sefaria.com