Astigmatism occurs when light entering the eye does not converge at a single focal point in the back of the eye, but instead focuses at two different locations. Visually, this causes images to appear smeared / elongated, due to the distance between these points, and degrades vision at both distance and near. The most common cause is due to a non-uniform corneal surface, where the curvature is greater in one meridian (plane) than the other but can also be caused by the crystalline lens of the eye. Visual correction for patients with astigmatism requires different optical powers in two different meridians (a spherical and a cylindrical component) in order to refocus the two focal points back into one single point. In order to accomplish this effectively, the use of spherocylindrical spectacle glasses, toric contact lenses, refractive surgery, or a toric IOL is required, as these options allow for the correct power at both meridians. Correction using spherical equivalent power, without a discrete cylindrical component (sometimes referred to as “masking” astigmatism) will always result in uncorrected astigmatism and compromised visual quality relative to the magnitude of the astigmatism.
Astigmatism amounts of >0.75D (in at least one eye) occur in 47% of individuals. Of those with astigmatism, who are being corrected, 68% are corrected by eye glasses, 22% by spherical contact lenses, and 10% by toric contact lenses. Modern toric contact lenses have made significant improvements in design and surface technology allowing for exceptional comfort, stabilization, and vision making them an excellent option for astigmatic correction. Additionally, it has been shown that toric contact lenses provide superior visual acuity, visual quality, and functional vision, particularly during digital device use (less need to increase zoom and contrast) compared to spherical equivalent contact lenses even for low to moderate astigmatism making them the ideal choice of soft contact lens correction.