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Unlike a regular spherical lens, toric contact lenses with the addition of a cylinder effect optical surface are not symmetrical around their center and must be rotated to a certain degree for correct vision. While this is quite easy to accomplish with optical lenses fitted into an eyeglass frame, with a freely moving contact lens the task is a bit more challenging. Typical toric contact lenses are designed with the bottom portion of the lens thicker than the top. Gravity and the help of one’s eyelids pushing down on the lens during blinking, keeps the lens right side up and aligned with the right axis for correct vision.
This method used in many toric contact lenses has enabled patients suffering from astigmatism the option of ridding themselves of the burden of eyeglasses. However, this design does have its disadvantages with the lens frequently moving in the eye and often interfering with the lower lid resulting in a less comfortable fit. The thicker design also limits oxygen permissibility and creates a general feeling of discomfort in the eye.
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