AIS scooped the £1 million account following a three-way pitch against WWAV Rapp Collins and Target Direct Marketing in June last year.
Three months after winning the business, Alistair Bryan, the former client services director at AIS, who was closely involved with the RNIB account, was poached by Iris.
Jon Ingall, the managing partner at AIS, said: "We're still working with RNIB on its data auditing and brand development, but the marketing department decided to go their own way on the direct fundraising activity. We've still got a good relationship with it and we're continuing to progress on the work in the areas we still work on."
RNIB was unavailable for comment.