An unpublished study of nearly 1000 people in Japan with diabetes found that those people that ate about 2 pieces of fruit per day had a 40% lower risk of developing diabetic retinopathy (DR) over an 8 year period than people who ate about 1/2 a piece of fruit a day.
The study has yet to be validated and properly published and the researchers say that although eating fruit was linked to a lower risk of DR, they were not able to establish a cause and effect relationship so there may be other factors involved. Notably, all the participants were on a low fat diet so eating fruit may or may not be as effective in people with a high fat diet.
In any case if you're diabetic, eating fruit is not only good for you in the traditional ways we know about but seems to have some effect on DR so it's definitely worth a try.