What is "ba'Yom ha'Hu"?
Radak: Night is included in "ba'Yom" (Eli lied down at night).
Malbim: It was the same day that Ish Elokim told Eli about the curse on his sons. Hashem put this right after, so Eli would realize that Hashem deems it important and He will do to [very soon]. This is like "v'Al Hishanos ha'Chalom" (Bereishis 42:31).
What was Eli's place?
Radak: It was where the Kohanim sleep, inside (close to the Mishkan) than where the Leviyim sleep.
Malbim: It was his physical place, to sleep there. He did not lie in Heichal Hashem, to investigate and think about Kodesh matters, e.g. the Heichal and Aron. (Therefore, Eli was not so proper to receive prophecy.)
What is "Chehos"?
Radak: It is an adjective; they began to be weak.
Could he not see at all?
Radak: He could see, but not well. His eyes only started to be weak. It says also about Yakov "[v'Einei Yisrael Kavdu mi'Zoken] Lo Yuchal Lir'os", and afterwards 1 "va'Yar Yisrael Es Bnei Yosef" (Bereishis 48:10, 8).
Malbim: Yes, he could not see at all
Even though "va'Yar Yisrael" is written earlier, surely his eyes weakened before this! Also, "Kavdu" (past participle) implies that this was b what was mentioned above. (PF)
Why must the verse teach that his eyes were weak?
Radak: Perhaps it is a metaphor; it means that his heart's 'eyes', i.e. Ru'ach ha'Kodesh, was ceasing from him. It was not regular like it used to be, due to his sons' actions. Therefore, the prophecy came to Shmuel, and not to him.
Radak citing Midrash Shmuel 8:8: One who raises an evil son, his eyes weaken. We learn from Yitzchak and Eli.
