BEND, Ore. (CNN/Money) - Flexible spending accounts (FSAs) allow you to deduct pretax money from your paycheck and get reimbursed for health-related expenses up to an amount set by your employer -- typically a few thousand dollars.

The savings can be substantial. Paying for $2,000 in out-of-pocket expenses with income that was never taxed saves $560 in federal taxes for a person in the 28 percent bracket.

There's one catch: FSAs operate on a "use it or lose it" basis.

So if you still have money in your flexible spending account for 2003, it's time to get cracking.

The Internal Revenue Service sets guidelines for what is and isn't eligible for FSA reimbursement. And you'd be surprised by just how many items make the list, including acupuncture and contact lens solution.

But while most employers follow the IRS's guidelines for deductible medical expenses, employers ultimately determine what is and is not covered by an FSA.

"Employers can always be more conservative than what the IRS permits," said Andy Anderson, an attorney for Hewitt Associates. "I know employers who will not reimburse for any kind of contraception" even though the IRS considers contraception a legitimate expense.

Here are some common -- and not so common -- expenses to keep in mind.

Standard medicine: With costs rising as they have been, a relatively healthy family could save hundreds of dollars a year by saving for out-of-pocket medical expenses in an FSA. Premiums are not eligible for reimbursement, but deductibles, cost sharing for office visits and prescription drug co-payments are. Make sure you've claimed all of these costs for 2003. If you haven't saved receipts, the "explanation of benefits" sent by your insurance company should have information on what you paid on your own.

Perfect vision: Most plans will let you claim the costs of an eye exam, new frames, new lenses, contact lenses, prescription sunglasses, even contact lens solution. Or you can fix your eyes for good with laser surgery, which is not covered by insurance but is an eligible FSA expense.

Pearly whites: Your FSA money will also help fill in where your dental plan leaves off -- a big help if your kids need braces and other orthodontia or you need artificial teeth. Whitening procedures, however, are generally not covered. Nor are toothpaste, mouthwash and do-it-yourself teeth bleaching.

Weight loss: Most plans allow you to claim the cost of weight-loss programs like Weight Watchers and Jenny Craig, as long as your doctor prescribes it. Diet-plan booklets and weight-loss drugs may also be eligible expenses. "If you're 10 pounds over weight that's not counted," said Jay Coldwell, product director for Wausau Benefits. "But if you've been diagnosed as morbidly obese it probably is."

Smoking cessation: Smokers can sign up for smoking cessation programs and pay for it with FSA money. Depending on your employer's policy, you may now be able to claim over-the counter nicotine gum or patches.

Transportation: Don't forget to tally the mileage to and from your doctor's office -- you'll get 13 cents a mile for medical trips in 2003. You may also be able to claim meals and lodging if you needed to go far from home for essential medical care. The IRS also allows organ donors to deduct transportation and medical costs associated with their good deed.

Alternative medicine: There are all sorts of alternative treatments you can pay for out of your FSA, as long as they are viewed as medically necessary. Among them are acupuncture, chiropractic treatment, Christian Science practitioners and even massage if it treats a certain condition.

Cosmetic procedures: Generally, cosmetic procedures or products, such as plastic surgery, are not a legitimate expense. There are, however, exceptions for certain injuries, diseases or congenital abnormalities. If, for example, you lose your hair as a result of chemotherapy, you should be able to put FSA money toward a wig.

Assistance with disabilities: Guide dogs (and their vet bills), certain home improvements and school tuition are just a few examples of legitimate expenses if they are needed to accommodate a physical or mental disability.

The IRS recently clarified its rules for over-the-counter medication, giving employers the green light to accept claims for aspirin, cough medicine and just about anything that treats a specific medical condition. For example, vitamins may be covered if you're pregnant or have a diagnosed deficiency. Similarly, sun screen might be covered if you have doctor's orders to wear SPF.

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"It has to be for medical care and not just your general health," said an IRS spokesperson.

Some items, such as cold medicine, are clearly medical in nature, in which case a receipt with the date, amount and name of the item is probably all you need to get reimbursed, said the spokesperson.

But with dual-purpose items, such as vitamins or sun screen, you'll need a note from your doctor with a diagnosis and a recommendation.