What it means and why
Dk describes oxygen permeability of a material; Dk/t describes oxygen transmissibility through a lens of thickness t. In that relationship, material and thickness both matter. A quoted value should be read with its measurement convention and the lens power or thickness used.
This is one aspect of lens performance. It does not describe surface wetting, movement, deposits or infection risk, so a higher value cannot by itself identify the most comfortable or safest lens for a person.
A worked example
Teaching arithmetic only: hold Dk constant and double t; the ratio Dk/t halves. Real lens thickness varies across the surface and with design, so this illustration does not predict the oxygen exposure of every point on the eye.
What it does not tell you
High oxygen transmissibility is not permission to sleep in a daily-wear lens. Overnight approval, individual suitability and infection risk are separate questions.
THINK IT THROUGHCan two lenses made from the same material have different Dk/t?
Yes. Thickness is part of the ratio; compare values using compatible reference conditions.
Sources & reading notes
Page updated:
- ACUVUE · Oxygen transmissibility FAQ (manufacturer) ↗ Manufacturer information
Documents the maker’s specifications or positioning for a market; it does not establish independent superiority or personal suitability.
- CDC MMWR · Corneal infections associated with sleeping in contact lenses (2018) ↗ Public health information
Useful for general health explanations and safety guidance; individual assessment and local advice still matter.
- ACUVUE · Product specification sheet (manufacturer) ↗ Manufacturer information
Documents the maker’s specifications or positioning for a market; it does not establish independent superiority or personal suitability.