Can a cleric cure spontaneous or acquired myopia (“nearsightedness”) with spells?
Which spell should she use if it’s possible?
Myopia is not a defined condition in D&D 3.5e: as a result, nothing in the rules causes it, and nothing in the rules fixes it. It just is not a part of the game. If you are playing by the rules, you are apparently playing in a game world where it simply does not exist. If you want to add it, you have to come up with rules for it yourself, and that includes both how you get it and how you fix it alongside what it actually does.
But a 5th-level cleric can cast the remove blindness/deafness 3rd-level spell which can cure the blind (regardless of how that creature came to be blind, so long as they actually still have eyes,1 and regardless of whether that blindness was permanent or temporary). So myopia should be handled, if by nothing else, by that. And since myopia involves far less damage to the eyes, as well as far less atrophy of the ocular centers of the brain, it probably should be curable by some lower-level spell—but since myopia isn’t defined, neither is that spell.
So the question becomes, what level should a hypothetical remove myopia be? Without knowing what game effects can cause myopia and what game effects myopia really has, that’s really hard to get right—spell level is generally influenced by balance more than anything else—but we can look at what various spell levels offer. Since 3rd-level spells include remove blindness/deafness, we know we have to be talking about a 0th-level, 1st-level, or 2nd-level spell.
The closest we get in 0th-level spells (aka orisons) are mending, which fixes a broken object, and purify food & drink, which makes things safe to ingest. Neither fixes a damaged body, which is more complicated than an object, so it seems that orisons are not up to this challenge. There is also cure minor wounds, which heals 1 hp, but hit points are a nebulous abstraction that are difficult to turn into narrative terms, so that doesn’t help us.
In the 1st-level spells, the only condition-healing spell is remove fear. Fear is a transitory, emotional experience, not an injury, so probably easier to fix than myopia—but then, remove fear also covers supernatural fear, so it’s hard to say.
With 2nd-level spells, we get remove paralysis, which again heals paralysis from any cause, regardless of how long that paralysis would otherwise last. Healing a mangled spinal column is massively more complicated than healing myopia, I would think.
So since remove paralysis seems far more powerful than remove myopia, but mending seems weaker, that leaves remove myopia sitting pretty comfortably in the 1st level of spells. That means that any cleric, of any level, is capable of curing myopia. Hiring a cleric to do so costs 10 gp, under the rules.
Notably, though, there is also the adept class, which intended for minor NPCs and which is what you’re probably more likely to find in a small town or village than a full-fledged cleric. And adepts do not receive remove paralysis or remove blindness/deafness as spells, so they might not receive remove myopia either. So someone might have to travel into a bigger town or city to find a cleric to actually cast remove myopia. So if, say, a farmer doesn’t feel terribly inconvenienced by myopia, and doesn’t want to leave their fields to take that trip, and/or doesn’t want to spend the 10 gp tithe a cleric will likely charge for the spell, they might just live with it.
But an adventurer is going to be traveling anyway, myopia could seriously threaten their survival, and 10 gp is chump change for them even at low levels, and that’s assuming they aren’t already adventuring with a cleric who can do it free. An adventurer would basically never have myopia.
It is found in the trait rules in the Unearthed Arcana.
There is no known method for altering traits, once selected. However, a generous DM might allow the retraining rules to be applied, with any necessary tweaks.
As the trait rules are optional, not all groups will be using them. If not using them, a homebrew solution is the only other answer, as nearsightedness does not appear to be defined elsewhere in the rules.
Thus, no, a cleric cannot cure it, as odd as that may sound.