There are multiple ways to determine if the vitreous has detached. It can often be determined clinically during the exam. Using additional diagnostic testing such as B-Scan ultrasonography and optical coherence tomography can usually allow one to determine with good certainly whether there is either a complete or partial vitreous detachment.
The vitreous is transparent in that it is 99% water. But there are fibers within the vitreous made of collagen and other connective tissue elements. These can usually be appreciated with ease on exam during slit-lamp biomicroscopy of the vitreous.
Thank you for your thoughtful, honest - and prompt! - reply.
Sometimes you can tell - but it's not always easy. You have to have an excellent view. My retinal specialist friends can usually tell a little better than me. So the answer is sometimes you can tell - it all depends on your view, and your skill.
Michael Kutryb, MD