When should I use a bitoric lens design?
“Definitely a -2.50 or greater corneal cylinder should be considered for a bitoric design. Many times a low eccentricity (0.50 or so) back surface aspheric design will work if it is fit a little steeper than average. However, the topography will tell the most as to when a bitoric is indicated as a good design.” (Jim Slightom, ABB Concise)
“Anytime it would improve fit and/or vision. This may be as little as 1.5 to 2 diopters of corneal cylinder, depending on whether it is central or limbus-to-limbus astigmatism. Corneal topography maps can be especially beneficial in these cases. First, it can determined if the astigmatism is at all irregular, which may contraindicate a bitoric design. Secondly, topography can show if the astigmatism is central or limbus-to-limbus. In the latter case, toric peripheral curves are also typically indicated.” (George Mera, Tru-Form Optics)
“We consider a bitoric lens design at 2.5 to 3.0 diopters of corneal astigmatism. We also commonly manufacture aspheric back surface designs, which can often result in a successful fitting relationship in the 2.0 to 3.0 diopter toricity patients before a toric design is used.” (Mike Johnson, Art Optical)