GP lens eye Rounds

HIGH ASTIGMATISM: Toric Designs and Indications

Jessica Conroy OD, FAAO

Sphere Power Effect (SPE) Bitoric

• A bitoric lens that can rotate on the eye without induction of power and, therefore, without affecting vision¹
• Has two base curve radii and two different powers¹

Cylinder Power Effect (CPE) Bitoric

• A bitoric lens that can NOT rotate on the eye without induction of power and, therefore, ends up affecting vision¹
• Has two base curve radii and two different powers¹

Back Toric

• Toric on back surface and spherical on front surface of lens
  • Spherical power is made possible due to the induction of cylinder power when back toric lens is fit¹
  • Amount of cylinder included = 0.456 times the back surface toricity¹
• Requires well-centered and stable lens¹
• Minimizes problems like flexure, flare, and lens rocking¹

Sources

1. Bennett ES, Henry VA, Kinoshita BT, Lampa M. Correction of Astigmatism. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses, 5th ed., Wolters Kluwer, Philadelphia, PA, 2020:388–439.