What was the material used in old hard lens materials?

What was the material used in old hard lens materials?

• A. Hydroxyethyl methacrylate
• B. PMMA
• C. Silicone/acrylate
• D. Fluoro-silicone/acrylate

Answer: (B)

Early rigid (hard) lenses were made from polymethyl methacrylate, PMMA. This clear, stiff plastic provided excellent optical properties and durability, which made it the standard material for hard lenses for many years. But PMMA has low oxygen permeability, so while it keeps its shape and transmits light well, the cornea can receive limited oxygen during wear, a drawback that led to the development of newer materials. Hydroxyethyl methacrylate is the basis for many soft contact lenses due to its flexible, water-containing properties, not for old hard lenses. Silicone/acrylate and fluoro-silicone/acrylate are modern materials designed to increase oxygen transmission, used in newer rigid gas-permeable or soft lenses, rather than the classic PMMA hard lenses.

Early rigid (hard) lenses were made from polymethyl methacrylate, PMMA. This clear, stiff plastic provided excellent optical properties and durability, which made it the standard material for hard lenses for many years. But PMMA has low oxygen permeability, so while it keeps its shape and transmits light well, the cornea can receive limited oxygen during wear, a drawback that led to the development of newer materials.

Hydroxyethyl methacrylate is the basis for many soft contact lenses due to its flexible, water-containing properties, not for old hard lenses. Silicone/acrylate and fluoro-silicone/acrylate are modern materials designed to increase oxygen transmission, used in newer rigid gas-permeable or soft lenses, rather than the classic PMMA hard lenses.