We have developed a protocol to augment human sight to see into the near infrared range through human formation of porphyropsin, the protein complex which grants infrared vision to freshwater fish.

Retinal, or Vitamin A (A1), which is found bound to opsin proteins is a keystone of the visual pathway. The cone cells are granted sharp color vision by the complex photopsin. The rod cells which provide us with night vision and recognition of movement do so utilizing rhodopsin. Both of the complexes consist of a type of protein bound to retinal. Porphyropsin differs from this in that it doesn't use retinal, but rather a derivation called 3,4-dehydroretinol, or Vitamin A2 (A2).

The human body is fully capable of metabolizing and using A2; unfortunately the proteins which allow for transport through cell membranes have nearly 4 times the affinity for A1 compared to A2. We theorize that this can be overcome through a stringent Vitamin A1 restricted diet, supplemented with Vitamin A2.

But what would the point be of gaining infra-red eyesight?

I mean the main purpose. Please excuse my limited knowledge...

Probably there's no use for the common man, maybe it has some military use, but still it requires strict diet, so it's not something you could achieve just like that.(not to mention side-effects of lacking vitamin A).
I think wearing some googles or other equipment would be much better.