Hard contact lenses are still manufactured, but the technology has changed significantly from the original versions. The term “hard contact lens” is now replaced by the more accurate name Rigid Gas Permeable (RGP) lens. These lenses are rigid, meaning they maintain their shape on the eye, but their material is engineered for eye health. The modern RGP lens fulfills a specific and necessary role in vision correction that soft lenses cannot match.
The Evolution from “Hard” to Rigid Gas Permeable
The original hard lenses were made from a plastic material called polymethyl methacrylate (PMMA). While PMMA offered excellent optical clarity and durability, it was completely impermeable to oxygen. The cornea needs a constant supply of oxygen to remain healthy. With PMMA lenses, oxygen could only reach the cornea through the tear film exchanging underneath the lens with each blink.
This lack of oxygen transmission often led to corneal swelling, discomfort, and long-term health issues. The introduction of RGP lenses solved this fundamental problem by incorporating materials like silicone and fluoropolymers. These advanced materials are durable and rigid, yet they contain microscopic pores that allow oxygen to pass directly through the lens material to the eye. This gas permeability is the defining difference that made RGP lenses a safer and healthier alternative.
Why RGP Lenses Are Still Essential
The rigid structure of RGP lenses provides a superior optical surface necessary for correcting complex vision disorders. Unlike soft lenses, which drape over the cornea and conform to its irregularities, RGP lenses maintain their spherical shape. This shape creates a smooth, uniform refracting surface over the eye, which is critical for clear vision.
This characteristic makes RGP lenses the preferred solution for conditions like keratoconus, where the cornea thins and bulges into a cone shape. The rigid lens vaults over the irregular cornea, creating a tear-filled space that neutralizes the distorted front surface. This leads to significantly sharper vision than is possible with a soft lens. RGP lenses are also highly effective at correcting severe or high degrees of astigmatism, which is caused by an irregularly curved cornea.
Managing and Caring for RGP Lenses
The care routine for RGP lenses is generally more involved than for soft lenses, primarily due to the difference in material composition. RGP lenses require a dedicated, two-step cleaning process involving a daily cleaner and a conditioning or soaking solution. The cleaning step involves placing the lens in the palm and gently rubbing it with a specialized solution to remove protein deposits, oils, and microbes from the non-porous surface.
After cleaning, the lenses must be rinsed and stored in a fresh disinfecting solution overnight to keep them hydrated and free of pathogens. Never use tap water for cleaning or rinsing, as this can introduce harmful microorganisms to the lens and eye. Proper handling is also important because RGP lenses are smaller and more prone to being dropped than soft lenses.
Longevity and Replacement Schedules
RGP lenses are known for their exceptional durability, which contributes to a replacement schedule significantly longer than that of disposable soft lenses. With proper daily cleaning and care, a single pair of RGP lenses can often last for one to two years, and sometimes longer. This extended lifespan is due to the robust nature of the plastic material, which resists deposit buildup more effectively than softer materials.
Although the lenses themselves are highly durable, regular check-ups with an eye care professional remain a necessity. The lens may need to be replaced sooner if the wearer’s prescription changes or if the lens surface develops scratches or damage that compromise vision or comfort.