Praise then darkness, and creation unfinished

A couple of people I know have reported good results recently with ordering eyeglasses cheaply online. I'm tempted to get either a spare pair of the progressives; a pair of distance-only prescription sunglasses; or even both. The only thing is, their lenses are all polycarbonate. I had trouble with glasses a couple of years ago, which the optician suggested might have been because of the material. "Might" because it was also a different prescription. At that time, I went back to the other kind of plastic, and I made a point of ordering that for the pair I had made a month ago.

Any thoughts or advice--based on optics, materials science, neurology, or personal experience--on the topic are welcome. Here's what I posted two years ago, two posts a couple of weeks apart:

The optician--not an apprentice this time--adjusted both the earpieces and the nose pads, and it seems better, though I do keep reaching to slide them back a fraction of a millimeter. She also measured the previous glasses, and compared them, to try to figure out why I've been having some headache and eyestrain.
It turns out that the new prescription is stronger in both eyes for the astigmatism, but has lessdistance correction in the right eye than the previous. The right eye is where I'd been noticing strain. The plan is to wear these for a week or so--not switching back to the previous prescription--and see if that does the job. If it doesn't, I can get the lenses remade in the same plastic as the previous set; the new ones are polycarbonate, which is lighter, but it seems that any change can cause difficulties for the eyes and brain.

I'm returning my new eyeglasses, and having them remade in the plastic of my previous lenses, and without the self-darkening coating, for three reasons:

1. I'm still not quite adjusted to them, and the optician suggested that the problem might be the change to polycarbonate.


2. The darkened lenses let in enough light to cause eyestrain, because itgets in past the edges of the glasses. They also aren't entirely clear indoors, though the shading is subtle.


3. I cannot get them to stay clean for more than about five minutes, whether I use soap and water, the special cleaning stuff the optician sold me, or just my shirttail.

This means going back to the old, heavy glasses for at least a week, but it needs doing. I'd probably be returning them even if it were only that self-darkening lenses don't work for me, but I might have kept the polycarbonate if so.

These wouldn't be my only glasses--except in the sense that if I have a spare pair, and I lose or badly damage the main ones, I would use them instead of going back to the previous prescription while waiting for a new pair to be made.