system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] What sort of chemical was it that blinded Daredevil? What was its purpose?

In the modern superhero movies, there is a push to make the origins of most of the heroes more "realistic" as opposed to their comicbooky counterparts. The spider that bites Peter Parker is genetically altered rather than radioactive is TASM, Asgardians are aliens with advanced tech rather than real magic gods, the Infinity Stones are super advanced alien tech rather than pure magic, etc. 

So what is a somewhat realistic answer to what the chemicals Matt was exposed to were and what was the purpose of their existence? What causes them to change a person's biology?
gpt
a failed batch from oscorps attempts to recreate the super soldier formula. 

Richard Parker, Norman Osborn and Curtis Conners where attempting to create the super soldier serum for years before ideological problems arose forcing them to go their separate ways. while Richard and Curtis both believed that the answer lied in genetic manipulation Norman Osborn pushed for a more universal chemical option because he wanted to sell the formula as a weapon.

as a rich, amoral, genius, business man Norman Osborn was not unaware of the existence of a kingpin. they engaged in a mutually beneficial arrangement where the kingpin helped him off load dangerous and caustic mutagens from his labs. Norman saved money on proper disposal, was seen doing business with the kingpin by the more powerful criminal forces in the city (ensuring that they never bothered him) and the kingpin had a steady substantial income from a powerful weapons and tech manufacturer.  

when the Daredevil got blinded as a child he was exposed to a toxic recreation of the super soldier serum. entering through the eye ducts the chemicals burned out his optical nerves but went to work changing his physiology. it was a low enough dosage that he was able to survive with only disfigurement but a high enough dosage that he was able to benefit from it's positive effects.