The puff of air into both eyes measures eye pressure (well I think it does). To be honest, the eye test is very thorough, lots of different tests, looking into the eyes etc. If you are very worried about it, it might be worth booking a trip to an optician, who will charge you about £25 but will be able to give you a good idea of your chances of success.
There is a form that you can download on the CAA website that tells you what they are looking for, or not. The optician will be able to say if you meet their requirements.