My father has diabetes related retinopathy, can it be cured?

Controlled. Diabetic retinopathy can be controlled with laser therapy. To prevent progression of retinopathy it is essential that average blood sugar be optimized and blood pressure is kept in the normal range.
See eye doctor. Diabetes is a problem where the high sugars corrode the blood vessels in the eye and cause them to leak blood and protein. Most efforts by eye doctors are to keep the vision where it is at. Soemtimes there is improvement but all efforts need to be put on prevention with your pcp to control blood sugar and frequent checks with the eye md.