Which material is no longer used today and has a DK value of 0?

Which material is no longer used today and has a DK value of 0?

• A. PMMA
• B. SA
• C. FSA
• D. HEMA

Answer: (A)

Oxygen permeability through the lens material matters for corneal health. The DK value (oxygen permeability) reflects how easily oxygen passes through the material; a DK of zero means no oxygen can get through at all. PMMA, historically used for hard contact lenses, is essentially impermeable to oxygen, so its DK is effectively 0. Because the cornea needs oxygen during wear, PMMA-based lenses are no longer used for corneal lenses today and have been replaced by materials that transmit oxygen more readily. The other materials listed are oxygen-permeable: they include hydrogel and silicone-containing acrylates that allow significant oxygen passage, which is why they remain in use.

Oxygen permeability through the lens material matters for corneal health. The DK value (oxygen permeability) reflects how easily oxygen passes through the material; a DK of zero means no oxygen can get through at all. PMMA, historically used for hard contact lenses, is essentially impermeable to oxygen, so its DK is effectively 0. Because the cornea needs oxygen during wear, PMMA-based lenses are no longer used for corneal lenses today and have been replaced by materials that transmit oxygen more readily. The other materials listed are oxygen-permeable: they include hydrogel and silicone-containing acrylates that allow significant oxygen passage, which is why they remain in use.