TopGeek

I would just make the observation that, a one-week trial for someone who is already accustomed to gas permeable contacts, seems inadequate and unlikely to show anything other than whether or not you can adapt to them.
I also have a loss of central vision in one eye and tried daily, 15-day and monthly soft contacts in that eye over a period of three or four months. They were initially OK but I gradually found them more and more uncomfortable. Eventually, the hospital told me I had developed 'follicles' (yes, I thought they were hair roots) on the surface covered by the contacts and they told me to return to conventional glasses. I am still going through the process of finding out what sort of lenses I need.
Posterior vitreous detachment (PVD) is nothing to worry about, unless it has the complication that I suffered of incomplete detachment. It happens to most people eventually and most of them are unaware that they have it.
With the complication of your connective tissue disease, it's possible that your presenting symptoms are different to those of others but I would expect even the slightest tear in the retina to cause more dramatic effects than a floater - flashing lights, particularly in the dark.
Please bear in mind that opticians are not qualified to assess the medical status of your retina. If they see any abnormality, they should immediately advise you to see an ophthalmologist of your own choice - not one of their cronies with whom they may have an 'arrangement'.
I hope you get some satisfactory answers. Do let us know how it goes.