Questions of using the Alcon Toric Calculator.

[taurus1203]

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 ?

[taurus1203]

Thanks for your response.
It seems you also prefer using LRI to Torics lens.
Is it LRI easier to fine tune the amount of astigmatism to correct ?  Or there are some other complications of Toric lens ?
Thanks

[Ray T Oyakawa, MD]

I have used LRIs to almost 4 diopters of astigmatism and rarely use Torics.

The advantage of operating of the steep axis is that the LRI needed will be less.

Dr. O.

[taurus1203]

Dr Oyakawa,
Thanks for your advice first and I understand I need to think from the side of the surgeon.
I met 2 surgeons to have the consultation. The first one has a topograph machine and estimate I have only around 1.0 of astigmatism. He seems to be expert in LRI and told me he can comfortable operation on my incision at 90 deg to make my corneal more round and the result should be better than the toric lens. He also mentioned that depending on the final measurement and he may put one more small incision to keep the final residual astigmatism to be within 0.5 D and he thinks 0.5 D will not affect the vision.

The second one hasn't use the topograph for me yet (will use it when I decide to go for him) but he simply says that anything above 1.0 astigmatism should be easily fixed by a Alcon Toric lens and this can reduce the incision size.

I know you are strong in LRI and will you consider toric lens with astigmatism between 1.0 to 1.2 D.
Is it any real benefit to the put the cataract incision at the steep axis to make the corneal more round ?

Thanks