Contact lenses are a common method of vision correction. While most prescribed lenses are soft and flexible, Rigid Gas Permeable (RGP) lenses, or GP lenses, offer a distinct approach for specific visual needs. This article details the properties, applications, and practical considerations of GP contact lenses.
Defining the Rigid Gas Permeable Lens
A Gas Permeable lens is defined by its core material properties: rigidity and oxygen permeability. The “rigid” aspect means the lens maintains a consistent, stable shape on the eye, unlike a pliable soft lens. This rigidity is provided by durable plastic polymers, specifically fluorosilicone acrylate materials.
The lens material is engineered to allow oxygen molecules to pass directly through the polymer matrix to the cornea. This process is quantified by the Dk value, which measures oxygen permeability and promotes corneal health. This modern design distinguishes GP lenses from older hard lenses made of polymethyl methacrylate (PMMA), which were completely impermeable to oxygen. Contemporary RGP materials ensure a continuous supply of oxygen, which is necessary for the avascular cornea.
Comparing GP and Soft Contact Lenses
The fundamental difference between GP and soft contact lenses lies in their structural stability and interaction with the eye. Soft lenses conform to the shape of the cornea, whereas the rigid structure of a GP lens creates a smooth, uniform optical surface over the eye’s natural curvature. This dimensional stability often results in sharper, more precise visual acuity, particularly for people with astigmatism.
The fitting process for GP lenses is more meticulous, requiring custom measurements to ensure the lens rests correctly on the cornea and allows for proper tear exchange. Soft lenses, conversely, often use a more standardized fit that offers immediate comfort due to their flexible nature. A new wearer of GP lenses typically experiences a noticeable awareness of the lens initially, which often diminishes over a few weeks.
In terms of longevity and maintenance, the non-porous material of GP lenses resists the accumulation of proteins and lipids from the tear film more effectively than soft lenses. This resistance to deposits makes the lenses easier to clean and contributes to their durability. While soft lenses must be replaced frequently (daily, bi-weekly, or monthly), GP lenses can last for a year or longer, making them a cost-effective option over time.
Specialized Vision Conditions Requiring GP Lenses
The structural characteristics of GP lenses make them the preferred option for certain specialized eye conditions that soft lenses cannot adequately correct. Their rigidity is particularly useful in managing conditions where the cornea has an irregular shape. The lens functions by creating a reservoir of tears, known as a “tear lens,” between the back surface of the contact lens and the front surface of the cornea.
This liquid lens effectively neutralizes or masks the underlying corneal irregularities, transforming the distorted surface into a smooth, spherical one. This mechanism is especially beneficial for people with keratoconus, a progressive condition that causes the cornea to bulge into a cone shape. GP lenses are also commonly used for post-surgical vision correction, such as managing corneal ectasia—a complication that can occur after refractive procedures like LASIK. For these complex irregularities, the stability of the rigid lens provides a consistent focal point.
Handling and Adjustment for New GP Wearers
New wearers of Gas Permeable lenses should anticipate a brief adjustment period, as the eye adapts to the feel of the smaller, firm lens. This adaptation can take anywhere from one to several weeks of consistent wear before comfort levels improve significantly. Learning the proper insertion and removal techniques is an important part of the process, often involving methods like the blink technique or using a small suction cup for removal.
The cleaning regimen for GP lenses requires strict adherence to specific solutions designed for rigid materials. The daily routine involves rubbing the lens with an RGP-specific cleaning solution to physically remove debris, followed by a thorough rinse with saline solution. The lenses are then stored overnight in a disinfecting and conditioning solution. Never use tap water for rinsing or storage, as it contains microorganisms that can adhere to the lens surface and increase the risk of eye infection.