Sure.
As Mr. Harris mentioned, veterans can apply for benefits for anything that they feel is related to their service. It's part of that application process. They state, to the best of their ability, how they feel the service caused that condition.
The first step in the process is that Veterans Affairs verifies with a medical professional that the veteran has a diagnosed medical condition, and that's an important step.
Second, we have Veterans Affairs trained adjudicators, often nurses, who review the service records to validate that something happened during service, such as an exposure, an injury or an illness, that is the cause of their current medical condition. Those nurses have access to available research housed by the department from partners, other nations, etc. They also have access to specifically trained physicians who evaluate the research and help them with advice if they so need it. The nurses, the trained adjudicators, ultimately render their decisions based on the evidence on the files and the best available science of the day.