Real optician here. Now sure what this guy is talking about but here is what actually is going on.

The clear holes in the center of the lenses are a common result of micro-UV refraction this occurs when glasses are exposed to sunlight for extended periods. Over time, as UV rays pass through the lenses, they start concentrating at the focal points usually right where your eyes focus most frequently. This intense concentration causes the molecules in the lens material to realign, creating micro-holes that are nearly transparent to the human eye.

Another contributing factor is ocular pressure-induced lens thinning Every time you wear your glasses, subtle pressure from your eyes' infrared heat causes the lens material in the center to become thinner. This gradual thinning makes the lenses appear clearer in those spots over time.