Try not to worry too much, if it needed any treatment the letter would have informed you, and I think it's quite common when you change diet and get your levels lower, to have a little background retinopathy. The same thing happened to me on my first eye screening, every one since has been clear. I think it's the sudden drop in glucose levels when you sort your diet out that causes it.
As to whether it will deteriorate and you will need treatment in the future.
No one knows what the future holds, your best chance of avoiding any future eye problems is to keep your blood sugar as low as you can. For me it's all the motivation I need to keep on top of my diet and not let the carbs sneak in.