I agree, your vision insurance is most likely a different carrier as most insurance companies sub-contract their vision and dental out to other companies. Call the 1-800 number or local number on the back of both cards and inquire there. If they can't figure it out for you then you need to talk to your boss at work/human resources/accounting/whoever deals with health insurance at your place of employment.
Also, like Twinkie says it may just be cheaper to go to a retail vision place.
Please feel free to ask any additional questions.