In one sentence, describe what the following article is about:

Adding vision insurance to health insurance offered by your employer is usually inexpensive — often only an additional $3 to $7 a month. Purchasing your own is more expensive, but may still be worth it. Be sure to consider:  The total cost of the premium and copays, minus the amount your insurance will pay towards new glasses and contacts equals the cost of the insurance. Compare the cost of insurance to the cost of an exam and contacts without the insurance. You can check with the insurer before purchasing insurance to be certain that the doctor you prefer accepts their insurance. An FSA lets your employer deposit up to $2,550 of pretax money into an account that you can use to pay for eye exams, glasses, contacts, and contact lens solution. The income used for these purchases is tax-free. Be sure to save your receipts if using an FSA. They may be necessary to claim the money from your account. Look at past expenditures to estimate how much money you will be spending. It is better to underestimate your expenses than to overestimate them, because any money in your FSA account that you do not use in a calendar year will be lost, with two exceptions:  Your employer can provide a grace period of up to 2.5 months to use the money. Or, your employer can allow you to carry over up to $500 per year to use in the next year.

Summary:
Calculate costs and savings from insurance. Make sure the eye doctor you use is in your insurance network. Ask if your employer offers a flexible spending account (FSA). Calculate your costs carefully before starting an FSA account.