Novice with Cataract lens questions

You're correct. By itself the degree of astigmatism you report doesn't justify toric lenses. You might ask for the surgeon's rationale.

First off this sounds a bit suspicious. Have you had the detailed eye measurements done in preparation for cataract surgery? They are done with instruments like the IOLMaster and Pentacam, and are used to determine the IOL lens power you need, and how much cylinder there is to correct. As you say there can be astigmatism (cylinder) in both the natural lens and in the cornea. And, some of the astigmatism in the lens can be the result of the cataract itself.

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The pre-surgery eyeglass astigmatism is the total of the lens and cornea astigmatism. Because the effect has an angle the astigmatism in the lens can be at a different angle than that in the cornea. They can offset each other, or they also can be additive. That is why you need a predicted residual astigmatism after the lens is taken out of your eye and the lenticular astigmatism is gone. These instruments can do that. Until you get those measurement I would not make a decision. You should ask for the IOL Calculation Sheet which will have these numbers in it.

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My personal experience with both eyes was that my eyeglass astigmatism was significantly reduced with a non toric lens. In one eye my eyeglass cylinder went from -2.75 D down to -0.50 D after surgery. In the other it went from -1.25 down to -0.75 D. If your -0.25 D was to increase after surgery, it is possible, but I think highly unlikely.

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The other issue is as you have identified correctly is the minimum cylinder power of an IOL. Alcon (AcrySof IQ Toric) and B+L (enVista Toric) make lenses that have a minimum cylinder power of 1.0 D. This is at the lens plane, which translates into 0.75 D at the cornea or eyeglass plane. Other manufactures have a minimum power which is higher still as you note. The standard practice is to not over correct astigmatism, as it can flip the angular position of it. For that reason the minimum power corrected is -0.75 D or more, and only with the lower power lens like the Alcon and B+L ones.

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So as I say, I would not even think about going ahead with a toric unless they give you the predicted residual cylinder for each eye.

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As for cost I can tell you where I am in Canada the basic monofocal is free. The monofocal toric (Alcon AcrySof IQ Toric) is $1,100 CDN per eye. That is an extra cost over the monofocal. $8,000 US? for two torics sounds very very high.

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As I say this is suspicious. Perhaps time to get a second opinion from another surgeon...

Hi RonAKA,

Thank you for such a comprehensive reply. The attachment didn't attached, but no worries, a quick google and I was able to d/load.

I did mention that I would provide feedback after my office visit. I didn't speak to the surgeon but one of her techs who could view the calculation spreadsheets. What I learned follows on ...

• They do use IOL and Pentacam, and they do have the data sheets. I can view my sheet if I sign a release (which I will do in a day or so). I'll then be able to use your guide to help decipher the numbers!
• She did give me the predicative residual eye glass prescription: L +1.00 R +0.75.
• I had been offered standard or premium lenses: when I quizzed her regarding the use of toric lenses for low values, she told me that I was NOT a candidate for toric lenses (JUST AS YOU PREDICTED!).
• When I quizzed further, I was told that they would insert a standard distance lens, and then immediately carry out further a laser surgery procedure to correct the astigmatism. I didn't catch the terms she used but it wasn't lasik.
• This all very strange ... I listened closely to the surgeon, and as an engineer I'm used to dealing with numbers, and I was left with the distinct feeling that I was being up-sold. I was never informed that this isn't a lens-related fix, and is an add-on procedure, by her or the surgery planner who went through all the insurance stuff. Weird!