It was sufficient merely to know that a cure existed.

No cure for the common cold exists, but the symptoms can be treated.

If one of these turned out to be the cause of Ezri's condition, then a cure might already exist.

Obesity is a complex disease for which no single cause or cure exists.

A biological madness for which no scientific cure existed.

No real 'cure' exists, the sufferer must simply wait for it to fix itself.

"If everybody thinks the only people who need the cure are dead or never existed, why will it continue?"

A deadly plague for which no cure existed threatened to kill off all inhabitants of the world.

So, if a cure ever did exist, it might have been lost in that fire.

But for other eye diseases, no cures exist, only treatments that slow the loss.