Patients below 50 are likely to have WTR. The plus cylinder is in the 90 axis ( 90 degrees plus / minus 30 is taken as WTR.).
The Toric lens is rotated to a vertical axis.
With ATR astigmatism, the toric lens is rotated to a horizontal axis.
Baylor normogram teaches us that the back of cornea has against the rule cylinder. This back of cornea will nullify part of WTR , anterior corneal cylinder. This is mostly why this patient will not be accepting the full 2 cylinder at 80 and 100 that we see in keratometry.
Both Douglas Koch and Warren Hill advice leaving the patients will a little bit of WTR cylinder. This is to enable more comfortable vision and to neutralize the ATR shift in the anterior cornea that will occur as the cornea ages.
In my patients with 2 WTR cylinders I would minus 1.5 and implant the weakest available toric lens.
Upto 1.5 WTR I do not put in a toric lens.
In a patient in his 20s who is likely to retain WTR for 30 yrs of more It will be best to target for zero post op cylinder and I would probably undercorrect by one step from the Alcon toric calculator.
Current thinking is that the best toric lens calculator in the world is the Barretts Toric calculator. This is free at the ascrs web site. Please try it out for your patient?
http://www.ascrs.org/barrett-toric-calculator
It takes into account, posterior corneal cylinder, unlike the Alcon toric calculator site.
Inputs from Dr. Ramesh D.