Blackstone is right there is evidence that a rapid lowering of control will increase the speed of progression. This is where why I live a fluorescein angiogram of the eyes is required before people go onto pump therapy .If theres existing retinopathy and a high HbA1c, they are advised to alter things slowly and monitored more carefully
As Kegstore says, its a dip, and doesn't happen to everyone . After 3 years of good control progression slows to below the 'average' rate..
Except in a few cases, it only occurs if there was retinopathy in the first place. At the Good Hope hospital in ' Birmingham ' 32% of patients with retinopathy progressed as their HbA1c was lowered, here, whereas only 2% of those with no retinopathy progressed.'
Its wrong to think that any improvement in control 'caused' the damage because keeping levels high may well have caused even more serious problems. In the long term, better control is the only sensible option.
Incidently slowing progression doesn't just involve glucose levels. its a salutory lesson for all of us to read that there is a linear relationship between blood pressure and retinopathy ,a near linear one with lipids and a probable near linear one with smoking.