Sforno on Genesis 27:1/ספורנו על בראשית כ״ז:א׳

1ותכהינה עיניו, just as what happened to the High Priest Eli who had not protested the wrongs committed by his sons. (Samuel I 3,13) In that instance the expression used is ועיניו קמה ולא יכול לראות, (Samuel I 4,15) Neither Avraham nor Yaakov experienced such problems in their old age at the age at which Yitzchok was struck by this affliction. They were both far older than Eli who died at the age of only 98. In fact, the Torah reports Avraham’s youthfulness in 25,1 when it reports him as taking another wife. Yaakov, with all the troubles he had experienced during his life was still able to see at 147 years of age, though with difficulty, (may be was very shortsighted then) as in Genesis 48,8 he is reported as clearly seeing Joseph’s sons, though they may have resembled each other so that he could not tell apart which one was Efrayim and which one was Menashe, This was in spite of the Torah (48,10) having told us ועיני ישראל כבדו מזוקן, “Yaakov’s eyes were heavy with old age,” (problems keeping the lids open?) At any rate, he could see, though not with clarity.