Hello, thanks for the query to H.C.M.C.
Your's query is that drug therapy is appropriate.
I will say, because treating physician know the condition of his patient better than others.
As far as concerned about eye sight ,if retinopathy
cured condition can improve somewhat.
The cause of swollen legs are hypo-proteinaemia ( microalbuminuria
is a type of protein and as it is passes in urine that's why there is deficiency of protein hence there swelling of legs.)
Since your's father is taking treatment from the last 15 yrs , so now it is the time to reassess the complete treatment schedule.
If your father's kidneys (both) are in good condition than please provide a full course of protein so that deficiency could be corrected.
Once the deficiency of protein is over the legs swelling will be alright.
Maintain a record of all treatment for diabetes
and related complications form it.