Jones matrix describing the action of the quater-wave plate

Hi there!!!!

I am having troubles with understanding about the representation of the Jones matrix for the QWP

I have the general form of the Jones matrix for the QWP: Q={{i, 0},{0,1}}. But after rotating it by a small degree of +/- ε, the new representation is Q_1={{i, +/-(i-1)ε},{+/-(i-1)ε,1}}. I understand that +/-ε comes from the rotation, but what the (i-1) term is about?

Anything helps,
thanks in advance,
vredina97