Residual Astigmatism: A Last Frontier of Cataract Surgery and a Perfect Result

Residual astigmatism remains a key complaint of patients and surgeons alike after what seemed like “perfect cataract surgery.” The issue is that the cornea, the window of the eye, can have a curvature that is more like a football than basketball. And this curvature can change depending on age, genetics, history of eye rubbing, dry eye issues, and general healing curves after cataract surgery. It can be very frustrating to chase after residual astigmatism, so surgeons try their best to address all of it before the surgery. Still, though, some astigmatism can remain or “come back.” In some patients, it is known that the general tendency for a certain axis of astigmatism to return despite all attempts to get rid of all astigmatism. 

In preparing for astigmatic correction during cataract surgery, the surgeon typically has the following options to correct corneal astigmatism:
1. Femtosecond Laser
2. Limbal Relaxing Incision (LRI) (a cut in the cornea on the steep axis of astigmatism) 
3. Toric IOLs 
4. Make the corneal incision on the steep axis of astigmatism: a surgeon may sit temporally (near the nose) or superiorly (near top of head) to help with this. 

Sometimes more than 1 of these techniques is used depending on the degree of astigmatism. 

Femtosecond Laser (#1), LRI techniques (#2), and/or  #4 can be used to decrease 1.5 D or less of corneal astigmatism. Toric IOLs are recommended in general if there is more than 1.5 D of corneal astigmatism (if there is no other pathology).

Here are the ways we Calculate what exactly needs to be done to remove Residual Astigmatism: 

1. The Barrett Toric Calculator is awesome and can be used with any IOL manufacturer.

2. The Alcon Toric Calculator is an awesome tool that takes into account the posterior corneal curvature (the inner part of the eye’s window shield). You can only use this with Alcon IOLs.

3. The LRI Calculator has fallen out of favor a bit since it does not take into account the posterior corneal curvature

What to do with Residual Astigmatism after the IOL Calculator says you have some astigmatism remaining?

1. Use Femtosecond Laser Assisted Cataract Surgery to address residual Astigmatism with the Laser.

2. LRI incision with a Diamond or Steel blade: Limbal Relaxing Incisions

What to do if the toric IOL rotates and/or astigmatism is still there?

The effect of a torsion (or turning) of the Toric IOL or misalignment of the Toric IOL on the refractive outcome worsens with increasing cylinder power of the Toric lens. For example, 5° of misalignment results in 17.5% loss of effect, but that translates into a loss of 0.18 D for a toric IOL with 1.03 D of cylinder power at the corneal plane and 0.71 D for an implant with 4.11 D of cylinder power at the corneal plane. This can make the difference between seeing 20/20 and seeing 20/40 without glasses. 

1. LRI incision with a blade: Limbal Relaxing Incisions. This is generally very safe with low risk of endophthalmitis, infection or complications.

2. Re-enter the eye to rotate the IOL: this is sometimes needed but carries all the risks of intraocular eye surgery: risk of needing another surgery, risk of infection, risk of loosing vision, risk of loosing the eye. 

To determine how to move the Toric Lens (ie, clockwise or counter clockwise): we use
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