Which method was the earliest used to manufacture soft contact lenses?

Which method was the earliest used to manufacture soft contact lenses?

• A. Lathe Cutting
• B. Spin Casting
• C. Hydration Molding
• D. Injection Molding

Answer: (B)

Spin casting allowed soft contact lenses to be made directly from a liquid hydrogel precursor by using centrifugal force to shape and cure the material in a mold. In this method, a monomer solution (often a hydrogel like HEMA) is placed between mold surfaces and the assembly is spun at high speed. The spinning pushes the liquid into a precise, curved form, producing a lens with uniform thickness and smooth surfaces. After polymerization, the lens is hydrated to reach its final soft, water-rich state. This approach, developed in the early 1960s by Wichterle and Lim, established a practical way to manufacture soft, comfortable lenses with good optical clarity. Other methods—such as shaping hard lenses by cutting material (lathe cutting) or methods that involve forming lenses and then hydrating or molding later—were not the earliest routes for soft lenses. Injection molding became more prominent later as production technology advanced.

Spin casting allowed soft contact lenses to be made directly from a liquid hydrogel precursor by using centrifugal force to shape and cure the material in a mold. In this method, a monomer solution (often a hydrogel like HEMA) is placed between mold surfaces and the assembly is spun at high speed. The spinning pushes the liquid into a precise, curved form, producing a lens with uniform thickness and smooth surfaces. After polymerization, the lens is hydrated to reach its final soft, water-rich state.

This approach, developed in the early 1960s by Wichterle and Lim, established a practical way to manufacture soft, comfortable lenses with good optical clarity. Other methods—such as shaping hard lenses by cutting material (lathe cutting) or methods that involve forming lenses and then hydrating or molding later—were not the earliest routes for soft lenses. Injection molding became more prominent later as production technology advanced.