20/20 correction
20/20 correction (full correction) is a correction you normally get from a licensed optician, which corrects your eyesight up to a degree of visual acuity that an emmetropic (or "normal-seeing") person achieves on a Snellen Chart, putting your blur horizon within 0.25 D of the chart.
If you can see 20/15 or even better, this means that you are overcorrected. (It is not necessarily considered super-human acuity, but it is unnecessary to correct to this level. Also, 20/15 isn't always a good measurement, as User:User can sometimes see 20/20 with blur horizon 0.5 D away, and overcorrection makes 20/10 readable on a bright Snellen)
It is very difficult or impossible to perform Active Focus at this level of correction, as there is not enough of a blur horizon to produce stimulus - see Distance vision.