Which DK value threshold is recommended for extended wear contact lenses?

Which DK value threshold is recommended for extended wear contact lenses?

• A. > 50
• B. > 75
• C. > 100
• D. > 125

Answer: (C)

Oxygen availability to the cornea when a lens is worn for extended periods depends on how permeable the lens material is to oxygen. The cornea gets its oxygen from the tear film, and wearing a lens can limit that supply, so devices with higher oxygen permeability help prevent corneal hypoxia and edema that can occur with overnight wear. Clinically, a relatively high Dk value is recommended for extended wear to ensure enough oxygen reaches the cornea even when the lens is in place for long periods. Lower Dk values leave the eye more at risk for hypoxia-related changes, while a higher value provides a safer margin. Among the options, the one indicating a clearly high Dk value aligns with this guidance, making it the best choice for extended wear.

Oxygen availability to the cornea when a lens is worn for extended periods depends on how permeable the lens material is to oxygen. The cornea gets its oxygen from the tear film, and wearing a lens can limit that supply, so devices with higher oxygen permeability help prevent corneal hypoxia and edema that can occur with overnight wear. Clinically, a relatively high Dk value is recommended for extended wear to ensure enough oxygen reaches the cornea even when the lens is in place for long periods. Lower Dk values leave the eye more at risk for hypoxia-related changes, while a higher value provides a safer margin. Among the options, the one indicating a clearly high Dk value aligns with this guidance, making it the best choice for extended wear.