These replacement lenses have more than 1 foci and can hence remove the dependence on glasses for more than 1 range. Bifocal lenses have 2 foci, one for FAR vision and one for NEAR vision. Trifocal lenses have 3 foci, one for each of the 3 ranges.
The need for glasses also depends on the shape of the cornea (the transparent tissue covering the black portion of our eyes). Most people have uniform (stigmatic) corneal surface (like a basketball), while some patients have a cylindrical (astigmatic) corneal surface (like a rugby ball). These patients require glasses to neutralize the distortion.
Cataract Surgery with TORIC lens implants provides an opportunity to neutralize the distortion of vision caused by rugby-ball corneas, and improve the quality of vision without glasses for these patients.
TORIC lenses are available in both single-focus and multi-focal variants.