If the minus lens center thickness is less than 1.00 mm, what does that suggest about the glasses?

• A. This pair of glasses is of foreign origin.
• B. The lenses are high index.
• C. The lenses are glass.
• D. The lenses are standard domestic.

Answer: (A)

Seeing a minus lens with a center thickness under 1.00 mm is a clue tied to manufacturing practices more commonly seen in foreign-made lenses. Lenses produced abroad are often thinned aggressively, using high-index materials and advanced thinning techniques, to achieve ultra-thin centers. Domestic production typically yields thicker centers, so such a sub-1 mm center thickness strongly suggests foreign origin. While very thin centers can result from high-index materials (a material property), the question’s cue is about origin, making foreign origin the best inference. The other options describe material or type characteristics, not the origin indicated by this unusually thin center.