I have been in this situation and having spoken to the passenger in question, been happy for him to sit by the exit. He was able to hear me perfectly well, despite my speaking fairly softly. As previously stated, glasses could also fly off during an incident. In fact, they are probably more likely to disappear than a hearing aid is. Switched on crew will use the emergency exit briefing as an opportunity to assess the passengers abilities to open the exits if needed, but, eventually, a certain amount of common sense and trust must come into the equation. If there is any doubt, they must reseat the passenger. Now, if only all crew were switched on, life would be perfect!
