What is the ruling on defrauding a health insurance company to gain a benefit for another person, such as purchasing prescription glasses or receiving treatment in the name of the insured, or buying sunglasses and registering them as prescription glasses to have their cost covered by insurance?

None of the described scenarios are permissible, as they involve lying, forgery, and unlawfully taking people's money. The perpetrator must repent and return the money to its rightful owners, or, if returning it is impossible, spend it on general Muslim welfare or donate it to the poor.

As for commercial insurance, if it is impossible to retrieve the paid premium or benefit from it to its full extent, there is no harm in using a stratagem to reclaim the right if it cannot be obtained through overt means. However, it is not permissible to subscribe to commercial insurance in the first place, and it is not permissible to benefit from it beyond the amount of the paid premiums.