I had a freckly on my retina an I ended up in the Oncology department of Moorfields ( didn't know wha Oncology was then, thank the Lord) It turned out to be a birthmark. I hope. Detected when they make you out your head in that puppet theatre box booth thing and follow the coloured lights.
Can you see your freckle or is it behind your own eye, IYSWIM?
These marks are very common and if your optometrist was worried, they would have referred you on to an ophthalmologist. Usually they are similar to skin freckles and need to be watched for any changes.
I have an iris freckle - a darker brown patch on the brown part of my eye. I was at the optician recently and they can now take a photo of it and store it on the computer to compare with futute images to see if there are any changes. He said it is like any freckle and to make sure to wear good sunglasses to protect it from the sun. I think it is strange that I have one in my eye as the rest of me is almost totally mole and freckle free.