'<Eyes ain't what they used to be>,' he said.

[park sang joon]

"Listen, how good are your eyes?"
"What do you mean?"
"A little ago, when we looked down on the fighting, could you make out the flag the attackers were carrying?"
"Eyes ain't what they used to be," he said.
["Trumps of Doom" of The Great Book of Amber by Roger Zelazny]
I'd like to know what "Eyes ain't what they used to be" means here.
Thank you in advance for your help.

 

[grassy]

It could mean that his eyesight isn't as good as it was when he was younger. It could also mean that nowadays people pay less attention to details than in the past.

 

[Barque]

By "eyes", he means his eyes.

My eyes aren't as good as they were earlier (when I was younger).

Cross-posted with Grassy - I agree with his first sentence but not his second.

 

[park sang joon]

I was such a fool.
Thank you, grassy, Barque, for your giving me enlightenment.

 

[Parla]

I agree with Barque.

 

[Keith Bradford]

"Things aren't what they used to be" is a cliché. As Fings Ain't Wot They Used T'be it was used as title of a musical in 1959.

Personally, I reckon that nostalgia isn't what it used to be...

 

[park sang joon]

Thank you, Parla and Mr.Bradford, for your so very kind answer.

 

[JulianStuart]

Personally, I reckon that nostalgia isn't what it used to be...

Ah, but it soon will be

 

[Hermione Golightly]

"The future ain't what it used to be" either, according to Yogi Barra and Meat Loaf. Ain't that the truth. Nostalgia papers the chambers of my heart.