Keratoconus Vs Astigmatism

It’s important to understand the difference of keratoconus and astigmatism when you’re looking for the proper eye wear. If a soft contact lens does not correct a vision problem, then the culprit may be astigmatism. Astigmatism is a defect in the eye or in a lens that is caused by a deviation from spherical curvature. The defect prevents light rays from meeting at a common focus, which results in distortion. If you feel you may have an astigmatism, then the rigid gas permeable (RGP) lens might be the better option for you.

Keratoconus is an eye condition in which a normally round, dome-shaped cornea can thin overtime causing a cone-like bulge in its place. If you feel you may have keratoconus, then the first step to resolve the issue would be to have a mapping of the corneal surface done. A corneal topography located the irregular areas on the front of the eye which prevent a lens from fitting properly.

What is a Hard Contact Lens?

A soft contact lens only lies on the cornea of the eye and does not fit over the irregular areas like a rigid gas permeable lens. If you have keratoconus, the rigid lens is essential because it provides the perfect dome shape for your football-shaped eye. As a result, light is able to focus better on the back of the eye giving the wearer superior vision as opposed to a soft contact lens.

Some patients are turned away from a rigid gas permeable lens because they’re worried about placing a rigid/hard lens in the eye for fear that it will hurt or scratch. At first, a rigid lens is more noticeable in the eye so it takes a little bit more time to adjust. However, rigid gas permeable lenses are breathable, safe, and more deposit-resistant than a soft lens.

Benefits of a Rigid Gas Permeable Lens (RGP)

A rigid gas permeable contact lens is ideal for patients who have two different eye prescriptions, which is a condition called anisometropia. The condition causes one eye to receive a different image size than the other. RGP lenses cut down the distance so the image size is more alike between the eyes.

Combining Soft and Hard Lenses for Optimal Vision

For improved comfort with an RGP for keratoconus, a soft contact lens is sometimes worn underneath it. This way the patient feels the soft lens against their eye and still has the visual benefits of a rigid lens. This technique if referred to as “piggybacking”. Another type of lens used is a hybrid where the RGP has a soft contact lens edge or “skirt” attached to it. This allows for better comfort and sharp vision. A third technique is using a scleral lens, which is a larger RGP that covers the cornea and white part of the eye or sclera. The large lens size may seem impossible to wear, but because the edge is away from the eyelid margins, it is not felt with every blink.

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