Like most contact lens wearers, you likely don’t think about the technical aspects or characteristics of contact lenses. For you and any other contact lens wearer, what’s important is that your contact lenses provide you with clear vision and are comfortable to wear.
That said, it pays to know about the different characteristics of contact lenses because, more often than not, it is these characteristics that determine how comfortable a contact lens is to wear.
Don’t know where to start? Not to worry. Lens.com is here to help you understand. In this post, we’ll discuss three important characteristics of contact lenses and how they affect eye health and comfort.
Wettability refers to the ease by which liquid spreads over the surface of the contact lens. Different contacts have different degrees of wettability, which plays a crucial role in how comfortable a contact lens is to wear.
Contacts with high wettability prevent changes to the surface of the eyelid that touches the lens when the wearer blinks. Wettability is also vital in preventing deposit build-up.
Advancements in contact lens technology have made contact lenses more wettable with the inclusion of wetting agents and more biocompatible with the human eye, making today’s contact lenses significantly more comfortable than they were a decade or two ago.
2. Oxygen permeability
Oxygen permeability measures the amount of oxygen that can pass through the contact lens to reach the eye. Every part of your body, including the eyes, needs oxygen, so oxygen permeability directly affects eye health and comfort.
The oxygen permeability of a contact lens is expressed using a numerical value known as Dk/t. D stands for diffusivity, which is how fast the oxygen moves through the contact lens. K stands for solubility, which is the amount of oxygen in the contact lens material. T stands for the thickness of the contact lens. Generally speaking, the thicker the lens, the less the amount of oxygen that can pass. A higher Dk/t value means higher oxygen permeability.
Compared to early soft contact lenses, today’s hydrogel and silicone hydrogel contact lenses have much higher oxygen permeability. Early contact soft contact lenses had a Dk/t value of less than 10, whereas today’s soft contact lenses can have a Dk/t value of 150 to 160.
Contact lenses with a high Dk/t or oxygen permeability allow the eyes to breathe, thereby preventing oxidative stress that can lead to eye conditions such as cataracts, keratitis, and ocular inflammation.
3. Water content
Do not confuse wettability with water content. As the term suggests, water content refers to the amount of water in a contact lens. Manufacturers express the water content of contact lenses using percentages. For example, the 1-DAY ACUVUE® MOIST contact lenses from Johnson & Johnson have a water content of 58%.
High-water content contact lenses are those that have a water content of at least 50%. It’s a common misconception that contact lenses with a higher water content are better for individuals who suffer from dry eye syndrome.
Contact lenses with a high-water content dry out more easily due to unavoidable environmental factors like pollution, dirt, and dust. Furthermore, high-water content contact lenses tend to pull moisture from tears, which can aggravate the symptoms of dry eyes.
There isn’t a “one-size-fits-all” approach to contact lenses. As such, no contact lens has the perfect combination of wettability, oxygen permeability, and water content. Contact lenses that work for you may not work for another individual, and vice versa, because you have unique eye requirements.
When choosing contact lenses, what’s important is that you listen to the recommendation of your eye care professional (ECP) and pay attention to how your eyes feel. If your current contact lenses are uncomfortable, then consult your ECP so that they can examine your eyes and prescribe you different contact lenses if necessary.