A blunder by Arsenal goalkeeper David Ospina has inspired a minor adjustment to the role of additional assistant referees, UEFA's chief refereeing officer Pierluigi Collina revealed Thursday. In Arsenal's 3-2 Champions League loss at home to Olympiakos last month, Dutch goal-line official Danny Makkelie stuck his arm out to signal that Ospina had dropped a first-half corner over his own line. Previously, additional assistant referees were restricted to making verbal communications with the match referee, but in an attempt to make their role more transparent, they will now be permitted to make arm signals in all UEFA matches."From tonight (Thursday's 2016 European Championship qualifying matches), additional assistant referees are allowed to make clear hand signals when the ball is fully inside the goal," Collina, a leading former referee, told the Leaders Sport Business Summit in London. Collina said that rule-making body the International FA Board (IFAB) had agreed to the change at the beginning of this week. Additional assistant referees were introduced to UEFA competitions in 2012 to rule on close goal-line calls and clamp down on penalty-area infringements. Managers have been known to question their purpose, but Collina says they play a vital role."Have you ever seen a duck on the water, relaxed but paddling like hell under the water?" said the Italian. "This is the additional assistant referee."