Discobolus, I’ve been thinking a lot about your post (as you might imagine, it piques my interest both professionally and personally). Unfortunately, there is scant literature concerning weightlifting and IOP, and no studies (that I could locate) looking at squats specifically (much less the extreme sort of squatting you perform).
Our understanding of IOP dynamics is represented by what is known as the Goldmann equation:
IOP = Episcleral venous pressure + (aqueous formation rate)/(aqueous drainage facility)
Aqueous drains from the AC into the episcleral venous plexus, which in turn drains into the cavernous sinus via the superior ophthalmic vein (this is a somewhat streamlined/simplified description, but captures the important points). In theory, episcleral venous pressure (EVP) equals central venous pressure (CVP). Note that the Goldmann equation predicts IOP should change mmHg-for-mmHg with changes in EVP (and therefore CVP). However, we know this is not the case, and that IOP is to some degree independent of EVP. For example, there are clinical conditions in which IOP falls below EVP, which (per the Goldmann equation) should not be able to happen. Likewise, the limited research concerning weightlifting and IOP found that, for most of the individuals studied, IOP did not rise in 1:1 fashion with CVP, although CVP was not directly measured (for understandable reasons–no IRB is going to let you thread a Swan-Ganz catheter into individuals who then do a triple at 595#).
All that said, there are data suggesting that a subset of individuals do not autoregulate IOP as well as others. For example, a minority of the individuals in the weightlifting-and-IOP study experienced much higher IOP spikes than did the others. Similarly, there are case reports of horn players with glaucoma who were found to have significant spikes in IOP while playing (horn-playing requires generating and sustaining high intrathoracic pressures, with a concomitant increase in CVP). Likewise, there are case reports of yogis with glaucomatous damage attributed to sustained IOP spikes incurred while in the headstand position (presumably via increased EVP secondary to gravity-dependent impeded venous return).
All of this is to say, I’m wondering if you are one of the individuals who does not autoregulate IOP well during spikes in CVP/EVP. Maybe your ophthalmologist should go to the gym with you and measure your IOP while you squat. (Kidding. Sort of.)
Edited for clarity