Toric contact lenses correct for astigmatism issues that arise from a different curvature of the cornea or lens in your eye (referred to as regular astigmatism, corneal astigmatism or lenticular astigmatism).
In these cases, the cornea or lens is curved so that the refraction of your eye differs between the vertical and horizontal planes. This causes blurry vision and trouble seeing fine details. Sometimes, vertical lines will appear to tilt.
The ability for toric contact lenses to provide different refractive powers on the vertical and horizontal orientations addresses this specific peculiarity that causes astigmatism.
Fitting is especially critical for toric contact lenses
Since toric contact lenses have a particular orientation, they need to stay on your eye in the correct way. Manufacturers design toric contact lenses with features to help the lenses stay put, including:
- Thin-thick zones
- Lens truncation, where the bottom of the lens is cut off a little
- Ballasting, where the lens is a little thicker or heavier
This means that the fitting the contact lenses to your eyes is even more important than usual. Toric contact lenses have a middle axis, like the Earth’s equator, that keeps your line of vision clear. If your lenses don’t fit well and slip, so does the visual clarity.