Im a Optical Lab Technitian working for a Optical Company, i make the lenses for peoples glasses. E.g we supply some specsavers outlets, vision express, but mainly the smaller companies.
For example a prescription comes in, i read it and decide which lense it needs and what base (Front curve) is right according to the prescription. I then see if it needs to be decentred (lense thats smaller so the segment needs to be decentred to a bigger lense according to the nasal.)or have a MAR coating (Anti-reflective coating).
I then put the prescription into the computer, do any little tweeks..EG..Make the lense thicker so it can go into a frame, move the heights of the segment..well theres loads of shit really lol
I then sag the lense, which measures the front curve of it and i the put this data into the computer.
Theres more complaicated shit but i cant be arsed to go into much detail.
