Which Nurse told you this?
Even with very good control you can shows signs of background retinopathy over a period of time, it's extremely difficult to avoid any changes to the eyes..
But things like mainatining good stable control, keeping blood pressure down all help to ensuring that you keep any changes to an minium level as possible.. Stable control is when your BG SD (standard deviation) is tight.. As if this is high the more likely what ever HbA1c you've got you will get damage to the eyes..
Raised blood pressure can also have an impact on eyes, as well as the kidneys hence why docs tend to be pretty swift in treating a slight raise in BP when they would even consider it in an non-diabetic
As to the Cinnamon, well its something that isn't going to hurt to try, but personally myself I don't buy into supplements etc.
Perhaps having a word with your DSN to review your medication and a chat with a dietitian to see if/how you may improve your diet etc..