Have you tried Sears? They usually have an optical store. Around where I live, there is a a Sears Optical that isn't even IN a Sears store. It is JUST an optical store. The optomtetrists hours vary, but the store itself is open even when he isn't there. They make adjustments to your frames when they get bent for no charge (pretty frequent need with a kid). And they run special's often. That is where I get my glasses from. Mine are pretty pricey, but only because I have a really strong prescription, and I like the frameless lenses... so they look like coke bottles if I don't get the ultra-thin lenses. And I like the anti-glare and other goodies, too. It all adds up. But my prescription doesn't change much and I can wear a pair for 3 years. A kid, they won't last that long, and their prescription may change often... so the cheapie deals that they offer (two sets for $99 sometimes) might be the way to go.
What insurance do you have? Our sears optical retailer gives us a discount for having Geico car insurance. And just for having BlueCross BlueShield, there is a discount on certain services/purchases. Be sure and ask what they offer discounts for... it may have no relation to whether or not you have "optical" insurance. We recently took out dental insurance, and as a "free" bonus, we receive optical coverage with a sister company that we don't pay anything extra for. Be sure and ask your insurer for other things if there are any benefits you might be unaware of.
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