So, now that Parental Glideance has come out, this raises some interesting questions. In that episode, a flashback shows that Derpy was apparently a pretty good flier and actually managed to outfly RD and some of the other Wonderbolts as a filly. What’s interesting is that at first her eyes are normal and worsen as time goes on, and she starts to place worse and worse in the races:  

 
Combining that with this, it looks like Derpy was a promising flier whose eye problems were hindering her performance, prompting an unsuccessful attempt at fixing the problem surgically.

I wonder if Derpy was blind at birth or something? And that Equestrian Medical Science had evolved enough to cure blindness?
 
It would explain why she can make her eyes look in different directions all the time. She never used them till later in her life, and now she uses them ambidextrously.
 
Of course, I’m trying to look at the silver lining this scene is showing. She had eye surgery earlier in her life, but it (probably) didn’t have anything to do with her cross-eyed look.

@Background Pony #9BD0  
PROTIP: If you do something to make others happy, you won’t make anyone happy.
 
So don’t worry, be Boxxy.
 

 
Be who you want to be. Fuck everyone else.

@Background Pony #9BD0  
Here is something to help you, if they make fun of how you look but you like how you look, fuck them.

@SeraphimDawn  
Just because her eyes are crossed in present time doesn’t mean it failed. I have strabismus, I corrected my eyes when I was little. My got crosseyed again much later, probably because I didn’t use my glasses enough (I quit using them after people kept making fun of me). I’m considering having a second surgery because now people make fun of me for my strabismus. I wish I knew people expect from me? They bully me when I’m crosseyed, but when I have surgery and use glasses to prevent it from returning they bully me for the glasses. I wish they were like Bronies and just accepted me with the eyes I have. :(

@Daneasaur  
Nah, only one of the nurses eyes is half closes, the other (her left eye) is wide open, meaning she has a raised eyebrow here, not a sad double eyebrow.

I guess they tried but failed to fix her eyes?

@Vree  
I’d like to think she got her teenage growth spurt earlier than Applejack.It’s more easy for the timeline this way

@Pagan  
She’s older than Jack here despite the pics you posted, so this is obviously Eternal Derpy the time traveller (the one who attended Twilight’s first sun festival)

@TheOtherPinkiePie  
I headcanon this since she still have her strabism as a filly

@Pagan  
Nevermind.
 
 

@Prof.NightJack  
Entirely possible. She is certainly not bothered by anything she’s being told…

This really isn’t far fetched. I had surgery on my eyes as a kid due to strabismus. Can’t say it helped that much.

@Daneasaur  
And then what the nurse actually says is “Why do you have bandages on your head? You’re here for an x-ray on you leg.”

derpy nnnnnnnnnnnooooooooooooooooooooooooooooooooo !!!! they fuck her eyes those bastards fuck her eyes !!!

Random observation: Derpy’s body shape is the same as AJ’s here (eg the “teenage filly” thin legs).

Perhaps the ole hit on the head with a shovel fan theory holds some water after all?

Judging by the doc/nurse there, she’s undergone a procedure and it was not a success… OR she did something that hurt her eyes and the nurse is delivering the “bad news”.

GO FANFICTION WRITERS! TO YOUR KEYBOARDS! THIS STORY MUST BE TOLD!

Did they imply she got her eyes through an injury? WTF?

Derpy getting treatment for her eyes?