At the airport here (Canadian city) a fairly large staff of US Customs and Immigration people check passengers, pre-board, bound for US destinations. Much of the travel is business-related.
In order to speed these passengers on their way, it has been proposed that frequent flyers register their retinal patterns at the airport. They would have their patterns read by the machine and be quickly passed through the boarding checks. There would be a fee for the service.
The airport authority is looking into the feasibility of the service.