Gas Permeable Contact Lenses
Gas Permeable Contact Lenses (GP) have been available in the United States since 1978, and they are a good option for patients with more complex or difficult prescriptions or those who require really precise vision.
Gas Permeable Contact Lenses were the next advancement in technology after hard contact lenses, and they are made of materials that contain silicone and fluorine as well as other additives to improve permeability and comfort. GP lenses are softer than their original counterparts, but they still hold their shape on the eye. This is why they are often called rigid rather than hard lenses.
These special polymer formulations make the materials very permeable to oxygen, and the surfaces of these lenses are evolved to be less attractive to mucous and protein coating from the tear film. In fact, they generally allow more oxygen to pass through than most soft contacts. All gas permeable contact lenses offer longer lens life and a flexible wearing schedule.
Types of Gas Permeable Contact Lenses
Gas permeable contact lenses are also called RGP (Rigid Gas Permeable) contact lenses, and oxygen permeable lenses.
GP designs are differentiated primarily by size. For many years virtually all GP lenses were fitted significantly smaller than the corneal diameter, typically 9 to 10 mm in diameter. As materials improved, larger lens designs became more common, the largest sometimes referred to as semi-scleral design lenses.
Recently there has been a resurgence of interest in larger scleral designs similar to what eye care practitioners were fitting in the 1950s and 1960s. Modern scleral lenses are made of very permeable materials. They are large (15 to 17 mm) in diameter to cover most of the eye’s surface, and are primarily used to manage complex eye conditions.
Gas permeable contact lenses are generally worn during waking hours, although some materials are approved—but infrequently prescribed—for overnight wear. In general, GP contact lenses are great alternatives for people who cannot achieve their desired visual correction with soft contact lenses, and they are especially helpful for patients who have medical eye conditions that cause corneal irregularity, such as keratoconus. GP lenses are also known to pose a lower risk of infection. GP lenses are usually placed in the eyes in the morning and then removed before bed.
Advantages and Disadvantages of Gas Permeable Contact Lenses
GP lenses are made of hard plastic and are always custom fitted. They are durable and have a longer lifespan than soft contact lenses. Modern GP lenses require a relatively short adaptation time compared to the old hard lenses, but they still require some getting used to. In contrast, most soft lenses provide relatively instant comfort.
One disadvantage is the size of a gas permeable contact lens compared to a soft lens. Most GP lenses are much smaller and are designed to move on the eye with each blink. This increases the risk of dust particles or other debris getting underneath the lens and causing discomfort or possible abrasions to the cornea, although this is less of a problem with modern designs. Their smaller size can also make them more prone to loss during vigorous activities such as sports, since they can be dislodged from their position. Because GP lenses must be custom fitted and are replaced infrequently, there is often little if any advantage to purchasing replacement lenses from sources other than the doctor or contact lens specialist who fitted them.
Are Gas Permeable Contact Lenses for Me?
GP contact lenses are great alternatives for people who have tried soft contact lenses but are not satisfied with their results. GP lenses are less popular than soft lenses, but they provide sharper vision for people with astigmatism, nearsightedness, farsightedness and presbyopia. Good candidates for RGP lenses include people who:
- Can tolerate the adjustment period
- Are unhappy with soft contact lenses
- Need multifocal or bifocal contact lenses
- Want to reduce their risk of infection
Caring for Gas Permeable Contact Lenses
When you receive your rigid gas permeable contact lenses, your eye doctor should give you a set of care instructions. Always follow your doctor’s advice before anyone else’s. Here are some tips to help you care for and maintain your GP contacts:
- Wash your hands before and after handling your lenses
- Only use cleaning products recommended by your eye doctor
- Never share your lenses
- Never top off old solution in storage case with fresh solution
- Always keep your storage case clean and sterile
- Avoid using tap water to rinse your lenses
Gas Permeable Contact Lenses and Orthokeratology
Orthokeratology is a non-surgical treatment that uses specially shaped GP lenses to temporarily reshape the cornea in order to eliminate nearsightedness. People who are best suited for Orthokeratology (Ortho-k) have nearsightedness less than -4.00 diopters and astigmatism less than -1.50 diopters. Orthokeratology is a great alternative for those who are too young to consider LASIK, those whose prescriptions are continuing to change, and those whose involvement in sports might be limited by wearing contact lenses. It reshapes the cornea in order to eliminate myopia (nearsightedness), so that you can see better at distance without wearing eyeglasses or regular contact lenses throughout the day. Ortho-k is safe for people of all ages, as long as their eyes are healthy. It is also called corneal reshaping or corneal refractive therapy (CRT).
Complications of Gas Permeable Contact Lenses
Although there are many benefits associated with rigid gas permeable contact lenses, complications can arise:
- Eyes may become dry at the end of each day
- Costs may be high especially for complex designs
- Adjustment period may be necessary
- Abrasions may develop if dust or debris enters eye
- Lenses may get lost due to their smaller size
- May not be as effective as eyeglasses or other forms of vision therapy
Talking to Your Eye Doctor
Here are some questions to ask your eye doctor about rigid gas permeable contact lenses:
- Are GP lenses available in my prescription?
- Do you think GP lenses are the best solution for me?
- How long should I expect the adjustment period to be?
- How should I store my lenses when I am not using them?
- Which cleaning products do you recommend for my lenses?
- How much will my lenses cost over time?
- How many follow-up visits do I need to schedule each year?
- What alternatives do I have to GP lenses?
- J. Anshel, MD “Smart Medicine for Your Eyes” (SquareOne Publishers, 2011) 332-333
- J. Anshel, MD “Smart Medicine for Your Eyes” (SquareOne Publishers, 2011) 329-330
- GP Contact Lenses, What Are GP Contact Lenses? http://www.contactlenses.org/whatare.htm
- The Journal of the British Contact Lens Association A. Jonathan Jackson, Clive J. Wolsey Contact Lens & Anterior eye – October 2009 (Vol. 32, Issue 5, Pages 204-206, DOI:10.1016/j.clae.2009.06.006)
- J. Weizer, MD; J. Stein MD, MS “Reader’s Digest Guide to Eye Care” (Quantum Publishing Ltd. 2009) 38