On the day Bryce Harper walked into the eye doctor’s office, he was, he would say later, “blind as a bat.” Keith Smithson, the Washington Nationals’ team optometrist, asked Harper to read an eye chart, then looked at him with astonishment and said, according to Harper: “I don’t know how you ever hit before. You have some of the worst eyes I’ve ever seen.”

That was on April 19. The next night, fitted with a new pair of contact lenses, Harper, batting just .231 at the time for the low-Class A Hagerstown Suns of the South Atlantic League, had a double and a single against the visiting Hickory Crawdads. The next night, he homered. And the night after that, he singled, doubled, homered and drove in six runs.

“It was like I was seeing in HD,” Harper said.

Suffice it to say Harper’s hi-def vision is a huge upgrade over standard-def. In 20 games since his visit to the eye doctor, Harper is hitting .480 (36 for 75) with a .547 on-base percentage and an .893 slugging percentage — with 7 homers, 10 doubles and 23 RBI. For the season, he is hitting .395/.473/.702, leading the league in all three “slash-line” categories.

Oh, and lest you forgot, he’s only 18 years old, the youngest player in the “Sally” League. His next closest pursuer in OPS (on-base plus slugging), first baseman Matt Curry of the West Virginia Power, is almost 23. Harper’s classmates at Las Vegas High — the ones he left behind after sophomore year to earn his GED and enroll in a junior college in order to speed up his draft eligibility — are preparing for their senior prom.

Harper’s offensive rampage, which includes a 16-game hitting streak that he continued Thursday night with a third-inning single against visiting Delmarva, raises two important questions:

How did Harper become the top amateur player in the nation in 2010, as well as arguably the greatest hitting prospect in Major League Baseball draft history, when he was “blind as a bat” prior to his being fitted with contacts?

And secondly, what in the world is he still doing here in Hagerstown?

To the first question, Harper merely shrugs and says, “I don’t know” — apparently being too modest to tell the truth, which is: That’s just how good he was.

“I needed [the contacts] in college,” he said. “But I tried them for a while in high school, and they gave me headaches really bad. So I just got by without them. But these are a new kind [of lenses], and they really help. The difference [in vision] is huge.”

The second question — why is Harper still in Hagerstown — is a bit more complicated. A promotion to high-Class A Potomac is almost certainly coming — just not soon enough to satisfy to legions of Nationals fans who want to see him promoted (ideally to Washington) today, if not yesterday.

“We haven’t had any discussions about moving him at all,” said Doug Harris, the Nationals’ farm director. “I know everyone wants to speculate about that. But he’s with a good group [of teammates]. He’s learning. Going through a league a second or third time — that’s a good challenge for a player.”

Pressed about Harper’s offensive numbers — and whether they might suggest he isn’t being challenged by Sally League pitching — Harris said: “I think there’s more to it than just statistics in this instance. He’s making great strides in all phases of the game. Offense is just one component of the game.”

Indeed, when you watch Harper play — as opposed to simply reading box scores or following his at-bats online — it becomes apparent he is still raw and prone to forehead-smacking mistakes on defense and on the base paths.

Over the course of two games earlier this week, Harper made a series of outstanding catches in right field (he is also seeing extensive action in center field), but also airmailed a throw to the plate that sailed into the netting behind the plate, some 15 feet above the ground. He also tried to throw behind a runner making a turn at first base following a single — even though the first baseman was some 20 feet from the bag.

The base paths provide another setting for adventure. On Tuesday, after singling to left field, Harper saw the left fielder bobble the ball momentarily and took off for second — only to be thrown out by 20 feet. It wasn’t the first time this season that Harper has been guilty of playing “Little League” baseball on the base paths — defined as running until someone tags you out.

“The hardest thing [for Harper] is realizing all these other players are better than what he’s played against before,” Hagerstown Manager Brian Daubach said. “And some of the risks he could take on the bases before don’t work here, and are not going to work at [the higher levels]. By no means do we want to take away his aggressiveness. It’s much easier to reel someone in than to try to get a passive player to be that aggressive. He’ll learn.”

As he has pretty much his entire playing career, Harper is also dealing with the scrutiny of opponents who want to show him up and hostile fans who want to get into his head. On one recent road trip, he barreled into an opposing catcher when caught in a rundown, causing the upended catcher — who had held onto the ball — to jump up and get in Harper’s face. Another near-brawl started when Harper exchanged words with a pitcher who had just struck him out.

“I’m not going to back down from anybody,” Harper said. “I’m always going to have my teammates’ backs, no matter what. I’ll be the first one out there swinging, if I have to. I’ve always been that way.”

In West Virginia, Harper also endured the taunts of one particularly obnoxious fan who peppered him all series with, among other things, vulgarities pertaining to his mother and sister — stuff that was described by one person who was there as “the most vile things I’ve ever heard anyone say, on or off a baseball field.”

Asked about that experience, Harper acknowledged having heard all of it. But then he shrugged again and said, “It’s just getting me ready for Philly.”