Not all costs are monetary, and some people are concerned about the plastic waste associated with contact lenses. That's especially true if you throw them away after a single use. One study found that 15% to 20% of users in the United States flush their contact lenses down the toilet, adding microplastics into wastewater. You may want to consider these kinds of life cycle costs, too, when deciding on a contact lens product or whether to wear eyeglasses.