the same way that drug companies can charge $140 for a bottle of eyedrops that costs 23 cents to manufacture, and another 6 cents for the bottle.
theres nothing stopping them if people are willing to pay (in the case of glasses) or have no choice (in the case of Rx)
yes i know there are other factors such as recovering research costs but thaose are generally a drop in the bucket compared to the retail cost.