No one could really say to be honest....
And thats because everyone's body is different.....one diabetic could run at 8.0% HbA1c for 25 years and nothing, where as another could run between 6 and 7% for three years and get retinopathy.....
They do say that background retinopathy is normal for long term diabetics, which I suppose is what, 10 years maybe.....
So, there's no answer.....all there is a day to day control, thats how you should look at it....