Albert Barnes Commentary 1 Samuel 3:2

"And it came to pass at that time, when Eli was laid down in his place (now his eyes had begun to wax dim, so that he could not see)," — 1 Samuel 3:2 (ASV)

The passage should be rendered this way: And it came to pass at that time that Eli was sleeping in his place; and his eyes had begun to grow dim; he could not see. And the lamp of God was not yet gone out, and Samuel was sleeping in the temple of the Lord where the ark of God was; and the Lord called Samuel, etc.

Eli’s old age and dimness of sight are probably mentioned as the reason why Samuel thought Eli had called him. As a blind and feeble old man, he was likely to call for help if he needed anything, either for himself or for the service of the temple.