Astigmatism cylinder - IOL vs Corneal vs Spectacle Planes?

[NightHawkGuy]

Can someone easily estimate the astigmatism cylinder value difference between the IOL vs Corneal vs Spectacle Planes?
I have seen in the specifications for toric IOLs, the maximum corrected cylinder is give in the IOL plane and sometimes in the corneal plane as well.  For example if the IOL plane cylinder is 2.75, it is reduced to 1.88 in the corneal plane.
In that example, what would the corresponding cylinder value in the spectacle plane (eyeglasses Rx cylinder value) be that the IOL could correct astigmatism for?

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?

[Joe_Traveler]

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.

[John C Hagan III, MD, FACS, FAAO]

There is no "simple answer"  the sphere and cylinder power of IOLs use complicated formula based on eye measurements, the type of IOL and a modification based on the surgeons preivous results.

[DocJFD]

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.  

[JohnHaganMD]

There are reliable formula for very long and very short eyes.

[JohnHaganMD]

DocJFD is a skilled cornea/cataract/refractive surgeon.

[NightHawkGuy]

Is this something that in real time during surgery that ORA can help with to get the astigmatism correction as close as possible, in selecting the closest available toric IOL?

[JohnHaganMD]

ORA is your best bet for real time at surgery checking of alignment of toric IOL

[NightHawkGuy]

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?

[JohnHaganMD]

No  first you have to decide whether to have surgery; then what your post op uncorrected vision; then what IOL only then measurements.

[NightHawkGuy]

But what if your decision whether to have the surgery or not depends on what specific IOLs would work and if additional laser corneal surgery would be required to make that decision?
I don't think I would make the final decision until all of that is known which would require the corneal measurements?

[JohnHaganMD]

Okay. I'm done.

[JohnHaganMD]

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.

[NightHawkGuy]

But would it be true that the spectacle plane cylinder value would be lower than the corresponding corneal plane cylinder, just as the corneal plane cylinder is lower than the IOL plane cylinder I see in the toric IOL specs?

Its looks to me like if my eye is 2.75D cylinder (eyeglasses Rx) I might require a toric IOL with 4D or higher cylinder in the IOL plane...