Dr Oyakawa,
I spent some time to play with the Alcon toric calculator and I think I understand a little more. I found some thing a bit strange and like to get help from you.
I tried some K number to give a little bigger corneal astigmatism than I have and assume the small incision is in the steep axis and my doctor thinks that make sense to have the corneal more round.
The Alcon calculator suggest me the following without using the Toric lens and with 0.86 D residual astigmatism.
Pre-Op Corneal Astigmatism: 1.13 D X 90°
Surgically Induced Astigmatism: 0.40 D X 0°
Crossed-Cylinder Result (corneal plane): 0.73 D X 90°
Anticipated Residual Astigmatism: 0.73 D X 90°
I also don’t understand why the Alcon Toric calculator doesn’t suggest a Toric lens as it seems adding a T3 at 90 deg can reduce the residual astigmatism. Is there any rule of thumb (like residual astigmatism is less than 0.9D) that a toric lens will not be used ??
If I move the incision location to 60 deg (this is just trial and error), the Alcon calculator suggests using the Toric lens and with the following result and less residual astigmatism:
AcrySof® IQ Toric IOL SN6AT3
IOL Spherical Equivalent (SE) 21.0 D
Axis of Placement 100°
Cylinder Power (IOL Plane) 1.50 D
Cylinder Power (Corneal Plane) 1.03 D
Pre-Op Corneal Astigmatism: 1.13 D X 90°
Surgically Induced Astigmatism: 0.40 D X 150°
Crossed-Cylinder Result (corneal plane): 0.99 D X 100°
Anticipated Residual Astigmatism: 0.04 D X 10°
Comparing the 2 scenarios, it seems the 2nd is much better as the residual astigmatism magnitude is smaller. Isn’t it? Or the other factors need to be considered like the axis of astigmatism, the shape of the corneal, the complication of having a toric lens ?
The most important thing is where the surgeon feel comfortable operating. A surgeon who operates temporally will have difficulty making an incision a 90 degrees.
You should discuss this with your surgeon unless you want operate on yourself.
Dr. O.