A Gas Permeable (GP) contact lens offers an alternative to soft lenses for vision correction. These lenses are technically referred to as Rigid Gas Permeable (RGP) lenses, a designation that speaks directly to their physical structure. Unlike soft lenses that mold to the eye’s shape, RGP lenses maintain their rigid integrity to provide a stable corrective surface.
Defining Rigid Gas Permeable Lenses
Rigid Gas Permeable lenses are made from durable, specialized plastic compounds, often including silicone, that are designed to hold their form on the eye. The term “rigid” distinguishes them from soft, pliable lenses. These lenses are smaller than soft contacts, typically covering about 75% of the central clear surface of the cornea. Their precise, stable shape is the foundation for the sharp visual acuity they provide, especially for complex prescriptions.
Mechanism of Oxygen Delivery
The “gas permeable” characteristic refers to the material’s ability to allow oxygen to pass through the lens matrix to the cornea. Since the cornea lacks blood vessels, it must receive its oxygen supply directly from the atmosphere via the tear film. Modern RGP materials are engineered with a high oxygen permeability (Dk) value, providing a direct pathway for this necessary gas. This material-based oxygen transmission supports corneal health and prevents issues caused by reduced oxygen supply.
The rigid nature and smaller size of the lens facilitate a second, highly effective mechanism for oxygen delivery called tear pumping. With every blink, the RGP lens moves slightly on the eye, creating a pumping action. This action exchanges the old tear film beneath the lens for a fresh, oxygen-rich layer of tears. This tear exchange is a significant factor in ensuring the cornea receives adequate oxygenation, which is crucial for maintaining clarity and preventing swelling.
Key Differences from Soft Contact Lenses
RGP lenses offer significantly sharper vision compared to soft lenses, particularly for individuals with astigmatism or high refractive errors. Because the RGP lens maintains a stable optical surface, it corrects vision more accurately than soft lenses, which conform to slight irregularities on the eye. However, the physical rigidity means that RGP lenses require a longer initial adaptation period, often spanning several days or weeks. During this time, the eye adjusts to the lens’s presence and movement on the cornea.
A major functional difference lies in their durability and replacement schedule, as RGP lenses are extremely robust. With correct handling, a single pair can last a year or longer, sometimes up to three years, offering a more cost-effective vision solution compared to disposable soft lenses. Furthermore, the non-hydrophilic material of RGP lenses is highly resistant to attracting protein and lipid deposits from the tear film. This resistance minimizes deposit buildup that can reduce visual clarity and potentially compromise eye health.
Practical Use and Maintenance
Daily Care Routine
Maintaining RGP lenses requires a consistent daily routine using specific cleaning solutions designed for rigid materials. The care system generally involves three steps:
- Physically cleaning the lens by rubbing both surfaces with an RGP-specific cleaning solution for at least ten seconds.
- Rinsing the lens with saline or an approved rinsing fluid.
- Soaking the lens in a fresh disinfecting and conditioning solution overnight.
Handling Precautions
Wearers must never use tap water for rinsing or storing RGP lenses, as it may contain harmful microorganisms that can lead to serious eye infections. Before handling the lenses for insertion or removal, individuals must thoroughly wash their hands with soap and dry them with a lint-free towel. Proper daily cleaning is the primary defense against deposit accumulation, ensuring the lens maintains its clarity and the eye remains healthy.