What's the difference? can anyone link me to a document on what this term means? I don't know if it effects the horizontal or the vertical? but also, like, what brands use which design? I'd like more info just out of general curiosity, but the reason this has been in my brain lately is semi specific as well....

Basically, at my current position working for a subcontracted vendor at the VA, I've been experiencing a few cases of what seems sorta like PAL non adapt but in people that have worn them jus fine earlier. And I'm not talking about them going form a Physio DRX to some no name PAL either, when I look at their old pair its also some no name PAL too, so I don't know what's going on.

Some of them are claiming the usual increase n distortion with a narrow visual field, etc, but the really weird cases are when they're saying the floor I coming at them or they have to raise their chin to read, BUT he RX hasn't changed, the frame size is about the same, and the PAL is in the same spot as before. This is what's causing me to wonder about hard VS soft PAL's and if one manufacturer is using more thinning prism than the other or if one power corridor is 'quicker'; or something. what the hell else could it be? what's the best way to check things like this can I use a lensometer or am I just supposed to know based o brand o something?


Any insight is greatly appreciated, this is one of those tings that's just sitting on my brain keeping me up night. Plus really just want to help these guys see.