Question:

I recently got an Request For Evidence letter from USCIS office, asking for more evidence of my "original contribution in the field", and reference letter of "independent" and "well-recognized" expert for my original contribution in the field.

I am now working at a university as a research associate. How could I get reference letter from independent and well-recognized expert for my original contribution in the field?

Answer: 

According to USCIS, the reference letter should come from independent and well-recognized expert, based upon his/her review of the documents that are submitted with the EB1 Extraordinary Ability application.

By "independent", the USCIS means an expert with whom the alien application has not worked before - not an employer, colleague, advisor, or client. By "well-recognized", the USCIS means a well-credentialed expert with lengthy experience in the field of endeavor.
 

The experience should include an advanced degree, more than ten years of experience in the field, a lengthy publication and presentation record.

Not every EB-1A application case needs the reference letter from "independent" and "well-recognized expert", especially when the alien applicant has Ph.D. degree and a lengthy publication record and several wards, which could distinguish the alien applicant from other individuals in the field.

http://www.greencardapply.com/question/question14/Independent-Reference-Letters_0303.htm