Only that x,y designate optional points in the X,Y axes , and {HEAD ~ z} of equation is {TAIL ~ a distance} of the optical axis direction from an optional point of coaxially aspherical surface to the XY plane 
is
Only that x , y designate optional points in the X , Y axes , and { HEAD ~ z } of equation is { TAIL ~ a distance } of the optical axis direction from an optional point of coaxially aspherical surface to the XY plane
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH