PMMA or S/A wearers should be refit into a lower/higher Dk?

PMMA or S/A wearers should be refit into a lower/higher Dk?

• A. Lower
• B. Higher
• C. Same
• D. Not specified

Answer: (A)

Dk is the measure of how much oxygen can pass through a contact lens material. The higher the Dk, the more oxygen reaches the cornea. For PMMA lenses, which have essentially no oxygen permeability, and for many S/A (soft/acrylate) materials that are less permeable than silicone hydrogel options, improving corneal oxygen supply is the main goal when refitting. That means, in practice, you look to move to a higher Dk material (often with a thinner lens design or a material that offers better oxygen transmission) to reduce corneal hypoxia and edema risk. So, the tendency is to refit into a higher Dk lens to promote healthier corneal physiology during wear. The option stating a lower Dk would reduce oxygen delivery and is generally not the preferred choice for PMMA or S/A wearers, unless there’s a very specific, context-driven reason not captured in the prompt.

Dk is the measure of how much oxygen can pass through a contact lens material. The higher the Dk, the more oxygen reaches the cornea. For PMMA lenses, which have essentially no oxygen permeability, and for many S/A (soft/acrylate) materials that are less permeable than silicone hydrogel options, improving corneal oxygen supply is the main goal when refitting. That means, in practice, you look to move to a higher Dk material (often with a thinner lens design or a material that offers better oxygen transmission) to reduce corneal hypoxia and edema risk.

So, the tendency is to refit into a higher Dk lens to promote healthier corneal physiology during wear. The option stating a lower Dk would reduce oxygen delivery and is generally not the preferred choice for PMMA or S/A wearers, unless there’s a very specific, context-driven reason not captured in the prompt.