A person of any nationality can apply as long as they are proficient with English.
As for eyesight, the following is taken from page 50 of
this JAA document:
"At the initial examination the refractive error shall be within the range of +5 to -6 dioptres
In an initial applicant with a refractive error with an astigmatic component, the stigmatism shall not exceed 2,0 dioptres."