You slip in your contact lenses in the morning with hopes of clear vision and ease throughout the day. By afternoon, however, your eyes feel dry, irritated and fatigued. Sound familiar? The culprit is one you probably haven’t even thought of — oxygen permeability.

What Exactly Is Oxygen Permeability?

Oxygen permeability, also known as Dk, measures how quickly oxygen passes through the contact lens material to reach your cornea.

The cornea, the transparent front part of your eye, lacks blood vessels and relies on oxygen from the air around it to stay healthy. When you place a contact lens over it, you create a barrier that allows or hinder this essential oxygen flow.

Why Should You Care About It?

Adequate oxygen supply to the cornea is crucial for several reasons:

Maintaining Eye Health

The cornea depends on oxygen to maintain its transparency and function. Lack of oxygen causes corneal hypoxia that can result in complications such as:

  • Corneal swelling (edema)
  • Redness
  • Neovascularization—the growth of new blood vessels into the cornea

These conditions are detrimental to eyesight and overall eye health.

Less Discomfort

A sufficient amount of oxygen is essential for the cornea to function normally and without dryness or discomfort. Contact lenses with higher oxygen permeability can retain moisture more effectively and cause less irritation in the eyes, which makes wearing them more comfortable.

Prolonging Lens Wear

Lenses with high oxygen transmissibility (Dk/t) are designed to allow enough oxygen to flow through the cornea to provide extended wear. This means you can wear them longer, even up to an entire night with less hypoxia-related complications.

Change in Contact Lens Materials

Contact lenses have come a long way since their inception. Early lenses were made from materials like polymethyl methacrylate (PMMA), which didn't allow oxygen to pass through, leading to discomfort and potential eye health issues. The introduction of soft hydrogel lenses brought greater comfort but still limited oxygen transfer. 

The game-changer came with silicone hydrogel lenses, which were developed in the early 2000s. These lenses combined the comfort of hydrogels with significantly higher oxygen permeability, transforming the contact lens industry.

How Is Oxygen Permeability Measured?

Oxygen permeability (Dk) is an innate feature of the lens material, and determines how much oxygen can get through. But when we think of the thickness of the lens, we mean oxygen transmissibility (Dk/t). Thicker lenses block oxygen flow, so the Dk of the material and the lens's thickness (t) is critical in determining the amount of oxygen reaching your cornea. 

The Risks of Low Oxygen Permeability

Wearing lenses with low oxygen permeability can lead to several complications:

Corneal Hypoxia

The cornea, deprived of oxygen, turns to anaerobic metabolism, leading to lactic acid buildup. This accumulation leads to corneal swelling (edema), resulting in:

  • Blurred vision
  • Discomfort
  • Sensitivity to light

As chronic hypoxia wears off, corneal sensitivity also declines.

Neovascularization

As a result of prolonged loss of oxygen, the cornea may develop new blood vessels extending from the limbus into the normally avascular corneal tissue.

This neovascularization is the eye’s attempt to pump in more oxygen, but can result in:

  • Scarring
  • Corneal thickening
  • Permanent vision loss (in severe cases) 

Increased Infection Risk

The hypoxic cornea is compromised by epithelial loss, and is susceptible to microbial invasions. This vulnerability can lead to infections, including microbial keratitis, which, if not treated quickly, could lead to:

  • Corneal ulcers
  • Permanent scarring
  • Blindness

Choosing the Right Lens for Optimal Oxygen Flow

When choosing contact lenses, you need to be thinking about factors that affect oxygen transfer to the cornea for comfort and eye health. 

Material

Silicone hydrogel lenses are designed to allow significantly more oxygen to flow to the cornea compared to traditional hydrogel lenses. The increased oxygen permeability allows for long wear times without adversely affecting the eye.

Lens Thickness

The thickness of a contact lens directly influences its oxygen transmissibility (Dk/t). The thinner the lens, the more oxygen will be able to flow into the cornea. But the material’s intrinsic oxygen permeability (Dk) is just as important.

Thus, lens thickness and the material of the lens must be taken into account to provide the right amount of oxygen to the eye.

Wear Schedule

Opting for daily disposable lenses reduces the chances of infections and problems in your eyes. Each day a new, sterile lens is used so the potential for bacterial growth with repeated use is reduced. This practice is healthier for your eyes and also convenient since you don’t have to worry about cleaning it every day. 

Recent Innovations in Contact Lens Technology

The contact lens industry is constantly evolving, with the most recent breakthroughs aimed at improving oxygen permeability and eye health:

Next-Gen Materials

Researchers are working on new silicone hydrogels materials with even greater oxygen permeability. These innovations will mimic the eye as closely as possible to give users maximum comfort and avoid hypoxia-related issues. 

Extended-Wear Lenses

New advances include lenses that can be worn for days or weeks. Made possible by materials that allow as much oxygen as possible to pass through them, these lenses are the perfect choice for those who want their eyewear to be comfortable without compromising eye health. 

But it is important to talk to an eye doctor to see if they are suitable for prolonged use.

Hybrid Lenses

Hybrid lenses, which combine the sharpness of rigid gas-permeable lenses with the comfort of soft lenses, offer a hard central section and a soft peripheral skirt. This design provides high oxygen permeability while providing comfort, which is why they are appropriate for people with special vision correction needs.

Tips for Contact Lens Wearers

The key to good eye health is to follow the best contact lens wearing instructions.

Consult Your Eye Care Professional

Getting regular eye exams is important to make sure your lenses supply your eyes with the oxygen they require and are healthy. A qualified eye doctor can give you specific information, keep track of potential problems, and suggest the right lenses for your lifestyle and eye health.

Follow Recommended Wear Schedules

It is required to stick to your contact lenses’ recommended wear schedule. Wearing lenses too long, particularly overnight, can cut off oxygen to the cornea, resulting in corneal hypoxia or infection. Always follow the guidelines provided by your eye doctor and the lens manufacturer.

Maintain Proper Hygiene

It is important to maintain proper lens care so that infection and other complications do not occur. Wash your hands thoroughly before handling lenses, clean them using recommended solutions, and store them properly. For daily disposable lenses, throw them away after each use for best eye health.

Prioritizing Oxygen Permeability for Optimal Eye Health

Understanding the value of oxygen permeability in contact lenses is crucial for your eyesight, comfort, and complete lens satisfaction as a user. By selecting lenses that allow for the proper flow of oxygen, and caring for your lenses in the correct manner, you can enjoy clear vision without compromising the health of your eyes.