Why can’t the Doctor deal with his condition?

In the episode “Oxygen,” the Doctor is exposed to vacuum for an prolonged period and

suffers blindness as a result of this exposure.

The Doctor reassures Bill that this condition is temporary, and that, once he has access to the resources within his TARDIS, he can deal with it (even if he has to implant the organs of a lizard).

BILL: You’re blind.

DOCTOR: I am? Well, that explains the bruised shins.

(Bill hugs him.)

DOCTOR: Oh, don’t get all gooey on me. It’s temporary.

BILL: Really?

DOCTOR: Yeah. Once we get back to the Tardis.

BILL: The Tardis?

DOCTOR: I’ve got stuff in there that’ll cure anything. Failing that, I think I’ve got some spare eyes somewhere. They’re from a lizard, but I’m sure they’ll fit.

_{Doctor Who, “Oxygen”}

Later, however, it is revealed that he is still blind, a condition which he believes will be permanent.

DOCTOR: Nardole, I can’t. I really can’t! I can’t look at anything ever again. I’m still blind.

_{Doctor Who, “Oxygen”}

Why is this? The Doctor clearly wants to have visual capabilities. He has access to all the medical resources of time and space (possibly including those of Gallifrey). Admittedly, there may be some that are too dangerous to be worth the bother of accessing, but we’ve seen highly advanced medical facilities that he’s been to before (New, New York, for example).

In addition, we know that the Doctor does indeed carry highly advanced synthetic body parts around in his TARDIS.

TANYA: You got your leg back?

DOCTOR: I had some spares in the medical bay. The Lothan, giant centipedes, experts in prosthetic legs. You’ll get the hang of it. You just have to train it to act like your own leg.

_{Class, “For Tonight We Might Die”}

How, with all these resources, is the Doctor incapable¹ of dealing with his blindness?

_{^{1: Besides, apparently, borrowing barely a few minutes of vision at a potentially ruinous future cost.}}

Answer

Out of universe perspective :

Having the doctor being blind allows several interesting dynamics.

Secret sharing with Nardole, but also it turns out to be necessary in the script of The Pyramid at the End of the World, where the blindness of the doctor is the reason of Billie's consent

Also has pointed out by Mr Lister, Moffat used it to bring back the sonic shades

In universe perspective

TLDR : He cannot regenerate only his eyes, and would not / cannot search a technology that would heal him

The Doctor do not want anyone other than Nardole to know about his condition. So he cannot use surgery that Nardole cannot perform himself. Moreover, a Time Lord body is precious. So even if he did not care about this secret, it is doubtful that the would implicate someone he does not completely trust. In this perspective, if the Doctor do not have the corresponding technology on the TARDIS, he probably would not acquire it not to risk exposing himself.

As for the regeneration, it is unclear if he can regenerate only a part of his body in case of localized damage. He is able to heal River's wrist in The Angels Take Manhattan, but number 10 in his first episode consider himself lucky to be able to have enough residual energy to regenerate his hand. So I'm tending toward "He cannot regenerate only it's eyes".