AK iron sight does not obstruct your peripheral vision like other optics will do (ACOG, red dots and others). As stated by Strelok, the accuracy and range of airsoft guns is limited to roughly 200 feets (200 feets can easily be reached with quality BBs combined a properly adjusted hop-up). It is still possible to attach optics by buying an AK scope rail.
Just remember that AEG (Excluding Semi-auto only DMR aeg) gets accuracy through volume of fire
; hence why Scope with magnification (low magnification like 4x is usually used) are used mostly by DMR (and BA of course) which have a limited rate of fire that requires higher precision to be effective.