Off-the-rack soft contact lenses across all manufacturers typically come in one or two standardized shapes, or base curves. These base curves were designed with the assumption that they would be fit on average corneal shapes. Soft contact lenses are designed to drape smoothly over the common corneal shape, but for patients with keratoconus, soft contact lenses either drape irregularly or rotate off-kilter due to the uneven nature of keratoconic eyes. The irregular draping of the lens leads to less-than-optimal vision.

Custom soft contact lenses can be designed to accommodate the patients with higher prescriptions as well. However, contacts can still rotate every time you blink, which leads to blur. Lastly, fully-custom soft contact lenses are to be discarded quarterly and tend to be less comfortable due to their thickness.

Gas permeable (GP) lenses (also known as “RGP” or “hard” lenses) represent the traditional form of contact lens correction, predating soft contact lenses. GP lenses were once the standard due to the simple nature of their design and their ability to reduce/eliminate much of the resulting astigmatism from keratoconus. But, there are very significant drawbacks to gas permeable lenses. First, adaptation to GP lenses is known to be difficult and uncomfortable, as the lenses rest on the most sensitive tissue of your body, the cornea.

Second, GP lenses are limited to the size of the cornea, which means that there’s less room for the lenses to stabilize on the eye, resulting in blur from the improper alignment of the lens. Third, accidental lint or dust behind the lens can lead to extreme discomfort, requiring the removal and reinsertion of the lens. Lastly, permanent scarring of the cornea can occur if the lenses are improperly designed and/or yearly lens updates are neglected.

Hybrid contact lenses are named due to the hybrid combination of two materials. The center of the lens utilizes GP materials (it’s a rigid lens in the center), resulting in clear vision similar to that of a GP lens. The rigid center of the lens is bonded to a soft contact lens “skirt,” which allows a softer edge to interact with the sensitive cornea instead of the hard edge of a GP lens.

In theory, hybrid lenses represent a perfect unity between clear vision and comfort, but in real-world wear, drawbacks still exist. The most significant issue with hybrid lenses is the lack of control of the position of the lens. Because hybrid lenses have a soft skirt, or lens edge, practitioners can’t predict how the soft material will interact with the eye.

With firmer materials, more accurate predictions can be made about how the lens will settle on the eye. The lens must always settle to a predictable location to maintain eye health in keratoconus eyes. The second issue involves the fit of the lens changing over time as the soft contact lens material wears. Resultant shrinkage and over-tightening of the soft contact lens material leads to lens irritation and discomfort. Lastly, Hybrid contact lenses can be more challenging to remove than the other contact lens options.

Due to hybrids being a second-line option among keratoconus experts, even the largest manufacturer of hybrid lenses has started offering scleral lenses as an alternative.