In contact lens materials, the Dk value describes which property?

• A. Oxygen Permeability
• B. Water Content
• C. Thermal Conductivity
• D. Refractive Index

Answer: (A)

Dk describes how easily oxygen can diffuse through a contact lens material. It reflects the material’s ability to let oxygen pass from the tear film to the cornea, which is vital for corneal health during wear. A higher Dk means more oxygen can reach the eye. Since actual oxygen delivery also depends on lens thickness, clinicians use Dk/t to gauge oxygen transmissibility, showing how much oxygen reaches the cornea per unit time. Water content affects wettability and can influence how much oxygen dissolves in the material, but it’s not the Dk value itself. Thermal conductivity and refractive index relate to heat transfer and optical properties, not oxygen diffusion. So, the Dk value is about oxygen permeability.