Although millions of Americans use some form of corrective lenses to see, when employers break out their vision plans as an ancillary benefit, the rates at which employees sign up for and use the plans drops dramatically.

For example, in 2008, the Bureau of Labor Statistics reported 42 percent of employees at large employers took advantage of ancillary dental plans, but only 16 percent participated in ancillary vision plans.

This is at least partially because many companies don't offer stand-alone vision plans at the same rate they offer dental ones; that same study showed 50 percent of large employers offered a stand-alone dental plan vs. 19 percent that offered vision plans. Clearly, many employers don't see the value in offering stand-alone vision coverage for employees, and it's increasingly rare to find an overall health plan that also covers vision.