Both Walmart and Target are so famous in retail industry of the world, and also have the similar style, like both of them try to set up the comfortable shopping environment with the pursuit of taste, quality and cheap fashion goods for the customers. Compared with Target, the price of goods in Walmart including the glasses is cheaper, but the quality is not as good as Target. So i would like to suggest you to choose Target.
First up, you gotta understand that Walmart, as the largest and most successful retailer in the world, must have developed profound relationships with glasses producers. Thus, they may be able to sell glasses at lower prices in contrast with other stores, and that's precisely they are constantly making big profits around the globe. Target, somehow, is inferior to Walmart in terms of scale, relationship with producers and after-sales service. But this principle isn't necessarily right, you can pay personal visit to both of their stores.
I think the Walmart is a better place to buy the glasses. The brands of eyeglasses there are much larger than the Target. In addition, there is always the discount activity. With the same quality of material and after-sale service, the price discount is really attractive. You should go to the Walmart and have a look.