I’m not a doctor, so I can’t be sure that Wisconsin coach Paul Chryst’s optometrist gave him the wrong prescription.

But if Chyrst legitimately saw Graham Mertz as Wisconsin’s best choice at quarterback over Jack Coan, it’s fair to wonder if he needs to upgrade to coke-bottle glasses. Or maybe sunglasses and a cane.

In Saturday’s 41-13 defeat to Notre Dame, Mertz was what he has continued to be throughout his Wisconsin tenure — the primary reason the Badgers lost. In 5 career games against ranked opponents, Mertz is now 0-5 with 2 touchdowns and 15 turnovers.

Against Notre Dame, Mertz threw 2 touchdown passes to the Fighting Irish, in the form of back-to-back fourth-quarter pick-6s, twice as many as he’s thrown to his own team all season — and infinitely more than he’d thrown to his own team this season entering Saturday’s game.

Mertz’s grim totals at Soldier Field: 18-of-41 for 240 yards with a touchdown and 4 interceptions. He has thrown one touchdown and produced 8 turnovers in this year’s losses to Penn State and Notre Dame.

To be fair, Coan wasn’t all that special against his old team. He took 5 sacks and finished 15-of-29 for 158 yards and a touchdown before leaving with an injury. But he was certainly better than Mertz. Not that it took much. And it’s reasonable to think this game would have a different outcome if Coan was still in a Wisconsin uniform.

Despite Mertz’s utter incompetence, Badgers fans should not direct their venom at a 20-year-old quarterback who looks like he should probably be starting at Wisconsin-Stout. This mess is squarely at the feet of Chryst and an offensive coaching staff that continues to see things in Mertz that clearly do not exist.

If Wisconsin wants to win the Big Ten — a goal that remains attainable given the Badgers’ talent at every position but quarterback — there is no choice but to make a change behind center. It doesn’t matter who it is. The worst thing a quarterback can do is create scoring opportunities for his opponent, and that seems to be all Mertz ever does. If there’s no one on the roster who can manage a game better than him, Wisconsin is in deep, deep trouble.

I have no idea what’s left for Mertz to show. We’re far enough into his career to see this is what he is: bad. The question is whether Chryst recognizes this before he invites another disaster against Michigan next week.

If he doesn’t, Chryst’s job may be the one that starts inviting calls for change.