It doesn't matter if the vision problem is due to PD or not.
He most likely has floaters. Hw should see an eye Dr.
What are floaters?
Floaters are small dark shapes that float across your vision. They can look like spots, threads, squiggly lines, or even little cobwebs.

Most people have floaters that come and go, and they often don’t need treatment. But sometimes floaters can be a sign of a more serious eye condition. So if you notice new floaters that appear suddenly and don’t go away, it’s important to tell your eye doctor.

Read more
https://www.nei.nih.gov/learn-about-eye-health/...

Floaters | National Eye Institute

https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/floaters

I have the same problem with the black dots. Also small black shadows in the corners of my vision. I was told that this is a fairly common problem with Parkinson's. It's pretty creepy!

We've seen an optician and no retina issues, thinks it could be due to parkinsons so awaiting a referral to see his specialist now

An ophthalmologist can check to make sure that they are floaters, which are common, or signs of something like retina issues.