How many different pairs of glasses should I own?

This is one of my favorite questions!  How many pairs of shoes do you have?  What do people see first, your feet or your face? Ideally, build your eyewear wardrobe to compliment your different looks and varied lifestyle needs. 

"When I was a little girl and started wear glasses, my mom took me shopping for 3 new pair every year.  Two pair of clear and one pair of sunglasses.  We would search for eyewear boutiques that had lovely selections. She believed that it was important for me to 'feel pretty' in my glasses. Since then, I have always considered them to be a primary accessory."  – Ruth