How do medical insurance companies determine whether a patient needs surgery or not? So, tomorrow I will be taking a vision field test because a plastic surgeon told me I was supposed to have done that before visiting him. Even though I haven't taken the vision test yet, the plastic surgeon already agrees that I need surgery because I have Ptosis (uneven or droppy eyelids) which impairs my vision sometimes (not most). So, I'm assuming the main reason I have to get a field vision test is that my insurance will know that this surgery needs to happen not because of cosmetic reasons, but because I need it in order to see properly. Now, I'm not sure if I will see perfectly fine during the test or not because my condition only effects me mostly when I'm tired or feeling uneasy. Will this mean I have to purposely skew the results of my test so it looks like I can't see well and my insurance will see that it's absolutely necessary for me to receive treatment?"