Both HSAs and FSAs allow you to pay for qualified medical expenses with pre-tax dollars. One key difference, however, is that HSA balances roll over from year to year, while FSA money left unspent at the end of the year or after a designated grace period is forfeited. That's why you often hear the phrase "use it or lose it" in conjunction with FSAs.
You may choose to use a Limited Purpose FSA to pay for eligible health care expenses and save your HSA dollars for future health care needs. You may use Limited Purpose FSA dollars to reimburse yourself for expenses not covered by your high-deductible health plan, such as:
Vision expenses, including glasses, frames, contacts, prescription sunglasses, goggles, vision co-payments, optometrists or ophthalmologist fees, and corrective eye surgery
Dental expenses, including dental care, deductibles and co-payments, braces, x-rays, fillings, and dentures