Contact Lens Overview

Dr. Diane Spada
A woman putting on contact lenses

In today’s contact lens market, there are many options and they all have advanced chemical makeup. Contact lenses can be classified in many ways, but the two main groupings are hard lenses and soft lenses. The soft lenses can then be subcategorized as listed below.

  1. Soft Lens – Hydrogels with high water content
  2. Soft Lens – Silicone Hydrogels

Hard lenses or rigid gas permeable (RGP) lenses offer some benefits over soft lenses. They are stiff and do not bend upon blinking, keeping the vision stable and sharp. They do not contain any water and therefore do not build up debris from the protein and lipids in your tear layer. They are very durable and do not tear as easily as soft contacts can. However, the one major disadvantage with hard lenses is that they have longer adaptation periods for comfort and thus many wearers choose soft lenses.

Soft hydrogel lenses with high water content have the ability to absorb significant amounts of water to keep the lens soft and pliable. The water content ranges from 38-75% by weight. It facilitates the pass-through of oxygen to keep the cornea healthy during wear, while simultaneously keeping the lens from drying out. Comfort with soft hydrogel lenses really depends on the wearer, but most wearers do experience good comfort (less dryness) and clear vision with these lenses. These lenses do not offer enough oxygen to the cornea to be approved for overnight wear, and are specified for daily wear with removal and cleaning every night. They are relatively inexpensive as compared to the soft silicone hydrogel lenses.

Soft silicone hydrogel lenses are relatively new and offer 5-6 times more oxygen transmission to the eye than conventional hydrogel lenses. All silicone hydrogels are considered low water content lenses. As silicone is added to the hydrogel material, the oxygen transmissibility increases but the water content decreases. Therefore, because of the silicone content, these lenses are usually given surface treatments and monomers to improve their wettability and comfort on the eye. Eye care professionals mostly prescribe silicone hydrogels for the increased oxygen transmission quality, and also because many wearers are not compliant with their eye doctor’s instructions for proper lens wear and replacement.

In summary, soft hydrogel materials are taking over the market share from hard lenses, while soft silicone hydrogel lenses are in turn taking the world’s market share from the soft hydrogel lenses. When it comes to comfort with wearing contact lenses, it really depends on the wearer. Some wearers will find that the soft hydrogels with high water content dry out quicker while some wearers will feel the silicone hydrogels do. It is always best to work with your eye care professional to see which lens will work best for you.

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