Gas permeable contact lenses, also known as rigid gas permeable (RGP) lenses, are a lesser-known alternative to traditional soft contact lenses. In this blog we will discuss how these contact lenses work and their benefits.
What are Rigid Gas Permeable Contacts Made of?
Rigid gas permeable lenses became available in 1979. Sometimes referred to as “semi-soft” lenses, RGP lenses are made with conventional plastics combined with silicone and a fluoropolymer, a special kind of plastic that is more oxygen-permeable. This is important because the cornea – the outer, protective layer of the eye – needs oxygen to stay healthy, and it gets oxygen from the surrounding air and tears.
Understanding RGP Contact Lenses
Unlike soft contacts that absorb water and are flexible enough to conform to the shape of the eye, gas permeable lenses work in a different way.
Stronger, more durable materials allow the lenses to maintain their shape when placed in the eye, yet the breathability of the lenses still allows oxygen to pass easily to the cornea.
Here is an overview of how these lenses work:
Permeability: Gas permeable lenses are actually better for your eyes than most soft lenses in terms of how much oxygen reaches the cornea. This is due to three characteristics:
- The special materials used in the lenses are more permeable to oxygen than the materials used in most soft contacts.
- RGP lenses are smaller in size than soft lenses, which means they cover less of the cornea allowing more oxygen to reach it.
- Since rigid gas permeable lenses hold their shape, they move with each blink. This action pulls tears, which contain oxygen, under the contacts further nourishing the cornea.
Sharper vision: The rigid nature of the RGP lenses and more customized fit allows them to maintain their shape, enabling light to more consistently focus on the retina to correct refractive errors to include irregular corneas from scarring, surgery, trauma, etc. This is particularly true for astigmatism correction. In contrast, the shape of soft lenses can change if they lose moisture and they are more prone to buildup that decreases visual acuity.
Durability: Rigid lenses are less prone to tearing compared to soft lenses. They are also longer lasting — if cared for properly, the life of a single pair of RGP can be more than a year. This can make them much more affordable than soft lenses that need to be purchased frequently.
Eye health: Rigid lenses do not absorb as much water, which keeps bacteria levels low and reduces the risk of eye infections. In addition, since the lenses do not retain as much moisture and have a smooth surface, they are also less prone to protein and lipid buildup, which can cause blurry vision, discomfort, irritation, or an immune response. Moreover, due to decreased oxygen permeability, wearing soft contact lenses can sometimes lead to corneal hypoxia, which is the deprivation of oxygen to the cornea that can lead to irritation, swelling, or cysts, although newer soft lenses that incorporate silicone are more oxygen permeable and reduce this risk.
Who Can Benefit from Rigid Contact Lenses?
Rigid contact lenses can take longer to get used to as compared to soft contact lenses and this, along with the difference in comfort, can mean RGP lenses are not for everyone.
RGP lenses can provide sharper, clearer vision for people with certain vision problems such as the following conditions:
Astigmatism: People with astigmatism have an abnormal curvature of the eye, making soft lenses more prone to moving and hindering vision. Rigid lenses hold their shape well, which decreases the chances the lenses will shift out of place.
Keratoconus: This condition causes the cornea to be cone-shaped instead of shaped like a dome. For those with mild keratoconus, rigid lenses are firm enough to help provide stability and compensate for the cornea’s irregular shape.
Presbyopia: This condition involves the inability to see images up close as you age. Most people turn to reading glasses as a solution, but RGP multifocal contacts can have multiple prescription powers in different zones of the contact. Clear vision is then possible across various distances eliminating the need for reading glasses.
Dry eye syndrome: The fact that tears flow beneath RGP lenses increases lubrication and the oxygen supply to the cornea, both of which can help reduce the symptoms of dry eye, which is why some people with dry eyes prefer these types of lenses.
