Dk/t Explained: Oxygen Flow in Contact Lenses Made Simple (2025)

When choosing the right contact lenses, there’s more to consider than just comfort and fit. One important factor affecting your eye health is the amount of oxygen your lenses allow to pass through. This aspect is often measured using Dk/t, and understanding this value can help you make better decisions for your eyes.

Let’s explore what Dk/t means and how it affects your experience wearing lenses:

First, let’s break down two elements of this term.

‘Dk’ is how easily oxygen can move through the material of the lens. On the other hand, ‘t‘ is for the thickness of the lens. Together, Dk/t means how much oxygen reaches your eyes while you’re wearing your contact lenses.

With these in mind, the Dk/t formula is Dk/t = oxygen permeability / thickness. When you divide the oxygen permeability by the thickness of your contact lens, it tells you how much oxygen is actually getting to your eye while wearing your contact lens.

For example:

If a lens has:

• Dk = 100 (high oxygen permeability)
• Thickness = 0.2 mm (thick lens)

The Dk/t value would be: Dk/t = 100 / 0.2 = 500

This means that the lens has a high ability to allow oxygen to pass through.

It has to do with wearing contact lenses overnight or all day.

Your cornea needs oxygen to stay healthy, but it doesn’t get it from blood vessels—only from the air. When wearing contact lenses, the oxygen has to pass through the lens to reach your eye. If your lens doesn’t allow enough oxygen, your cornea can become starved of oxygen, leading to discomfort, dryness, or even damage. Higher Dk/t means more oxygen gets through.

When you wear lenses for a long time, they block some of the oxygen from reaching your eyes. A higher Dk/t value is crucial for keeping your eyes comfortable. The more oxygen that gets to your cornea, the less likely your eyes are to feel dry, irritated, or fatigued.

To prevent discomfort and promote eye health, the Dk and t need to work together. If a lens is too thick (low t), even if it has a high Dk (good oxygen permeability), the thickness can still block some of the oxygen from reaching your cornea. On the other hand, if a lens is too thin, it might be comfortable, but it could lack enough oxygen permeability to keep your eye healthy.

Here are the ideal Dk/t values for different lenses:

Recommended value: Dk/t Above 24

Since your eyes get a break from the lenses overnight, they don’t need as much oxygen permeability compared to lenses meant for extended wear.

However, a Dk/t value above 24 ensures that oxygen flows smoothly to the cornea, keeping it hydrated and healthy. Without enough oxygen, your cornea can become starved of oxygen, leading to potential issues like blurry vision, dry eyes, and redness.

Here at Lens.com, we got daily disposable contact lenses like Proclear 1 Day (33 Dk/t) and Focus Dailies contact lenses (26 Dk/t). Here are other brands within the ideal Dk/t value:

Recommended value: Dk/t Above 100

These lenses are designed to be worn for longer periods, including overnight. Since they stay on while you sleep, they block the natural oxygen supply to your cornea. This makes a high Dk/t value crucial.

Values above 100 allow more oxygen to pass through even when your eyes are closed, ensuring your cornea stays healthy during sleep.

Here at Lens.com, we got contact lenses available for extended wear. Acuvue Oasys contact lenses has a 147 Dk/t that can last for six months at most.

Recommended value: Dk/t of 24 or Higher

Since toric lenses need to fit properly and stay in place on the eye to correct astigmatism, they must also allow enough oxygen to reach the eye.

A Dk/t value of 24 or higher ensures that toric lenses remain comfortable while providing adequate oxygen to the cornea. Although people with astigmatism generally require lenses with good stability, they also need proper oxygen flow to avoid dryness or discomfort.

Daily disposable contact lenses available at Lens.com include

Understanding Dk/t is key to maintaining healthy, comfortable eyes while wearing contact lenses. This important measurement tells you how much oxygen reaches your cornea through your lenses. Higher Dk/t values mean better eye health, with less discomfort, dryness, and irritation.

At Lens.com, we offer a variety of lenses with ideal Dk/t values for every need. If you have questions about which lens is right for you or need help selecting based on Dk/t, our experts are here to assist you.