You have a few options when it comes to buying vision insurance: namely, HMOs and insurance carriers.

You can also offer it under your business' cafeteria plan (click here for related article), which offers an array of benefits and lets employees pick and choose what they want.

Also check into your health insurance carrier. They can offer vision insurance as part of your health insurance policy, but it may be pretty narrow, covering only the bare minimum -- like routine eye exams.