For your first question, I'd suggest sending an opticians report to the CAA with a letter explaining your question. They are generally very helpful.
There are only 2 classes of aircrew medical under JAR; class 1 for professional pilots and Class 2 for non-professional.
The old UK 3 tier system now only applies to ATCOs, balloonatics and a few odd cases not covered by JARs. All the requirements are on the JAA website.