Clarification
We can actually compare eyeglass lenses to the structure of a bridge.
People with + prescription strengths (or people who wear glasses for near vision) must see the convex shape of the bridge, thus the translucent area. The convex area is situated on the outside of your eyeglass lenses.
People with – prescription strengths (or people who wear glasses for distance vision) must see the concave shape in the bridge, thus the structure. The concave area is situated on the outside area of your eyeglass lenses.