Polymethyl methacrylate lenses (PMMA lenses) were developed in the 1960s, and were the first ever prescribed to patients needing contact lens vision correction. These rigid lenses did not allow oxygen to pass through the durable plastic material to the cornea. Instead, when the wearer blinked, the lens would move, allowing the natural tears in the eye to transfer oxygen to the cornea. Since these lenses are not very comfortable, they are rarely prescribed to patients today.
Today, rigid gas permeable lenses (RGP) have replaced the PMMA lenses of the past. These durable contact lenses are much safer and more comfortable to wear, even for extended periods of time. For a more in-depth explanation, read on.
Frequent contact lens wearers generally know the difference between daily or monthly lenses or whether contact lenses are colored or not. There is another differentiator, and that is whether the contact lenses are soft lenses or hard lenses. This article will take a deep dive into hard contact lenses.
Conventional hard lenses were popular in the past. Known as PMMA, short for Poly (methyl methacrylate), they are not moldable to fit the eye as they are made of rigid plastic. Although they were durable and inexpensive, they also tend to be the least comfortable option for contact lens wearers, especially when first wearing them and the eye hasn’t adjusted to them. The lack of oxygen reaching the cornea may cause damage and be uncomfortable.
Alternatively, most hard lenses in the market today are rigid gas permeable (RGP) lenses made of materials that allow oxygen to reach the cornea while maintaining its shape on the eye. This reduces problems that may occur when the cornea does not get enough oxygen. They help slow the development of nearsightedness in contact lens wearers and correct refractive errors such as astigmatism with no distortion. Some RGP lenses are designed for extended wear (overnight). However, many eye specialists advise against wearing them for an extended period or while sleeping.
RGP contacts are incredibly durable, easy to care for, handle, and wear. They are more comfortable than PMMA lenses. However, RGP lenses cost more than PMMA hard lenses and are somewhat less durable. RGP lenses usually need to be replaced after 2 to 3 years of use. The RGP lenses can be quite economical compared to soft lenses, which require more frequent replacements.
The main disadvantages to hard lenses are their vulnerability to scratches. They can easily dislodge from the eye’s center position, and wearers may need to wear them consistently to grow accustomed to them.
If hard contact lenses are not as comfortable, you may be asking yourself, why do we still have them? Hard contact lenses may be required for specific prescriptions where soft lenses aren’t effective. These lenses can also be used to correct vision for people with unusually shaped or distorted corneas, such as astigmatism and keratoconus.
Either way, it is always good to be well-informed on the types of lenses in case one may fit your needs. Make sure to always check with your eye care professional before purchasing your contact lenses.