I have the same question: “Specifically, if my right eye has a 2.75 cylinder astigmatism (eyeglasses Rx, spectacle plane) what would approximately be the required cylinder value to correct it for a Toric IOL in the corneal and IOL planes?” In my own case, my spectacle cylinder is 2.5, my biometric measurements indicated astigmatism of 2.0, and the Toric IOL my ophthalmologist ordered for me is 3.0 cylinder. I have yet to have surgery.
Most formula assume a fixed ratio between the IOL and the corneal plane, based on the average pseudophakic human eye (ie, 1.46 D at the IOL plane = 1.00 D at the corneal plane, and 1.00 D at the IOL plane = 0.68 D at the corneal plane). In long and short eyes and eyes with deep or shallow anterior segments these assumptions may be confounders to optimal results. A surgeon will decide on factors at time of surgery that would optimize the result for given individual.
It would seem like the eye surgeon needs to do full measurements of my eye's cornea right away in order to be able to decide which toric IOLs and/or possibly laser corneal LRI/AK surgery would be appropriate for my eye's astigmatism?
Should I request that at the initial consultation/exam?
No its not easy. Complex formula based on A constants of the IOL, corneal astigmatism and A scan measurement of different parts of the eye.