Al Bundy would not get his glasses right away. Obviously, prescription glasses require a few hours to a few days to make, depending on the prescription, special finishes, etc.
Al Bundy says his vision is perfect. But his last eye exam was had when he was in fourth grade. Obviously, his vision had deteriorated considerably in 40-plus years.
The table mirror in the store is only a frame so the camera can shoot Al's facial expression from behind the mirror when he tries out the glasses.
When Al holds the framed photo of Peg to get a clear look at it, he is holding it at torso level at an almost 90 degree angle, which would not be conducive with him being able to see it properly. This was presumably done so the camera/audience could see it properly, and possibly also so it wouldn't reflect the studio lights.
Al is shown here to be enjoying and even singing along to the theme song for "The Facts of Life." However, later episodes show that Al absolutely despises that theme song. And even wishing death on whoever wrote it.