BLOG: How can you tell if your patient’s toric IOL has rotated?
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Toric IOLs are beloved for their ability to counteract astigmatism accurately and safely. However, they do come with an increase in risk for your patient.
There is a small chance of the IOL rotating inside the capsular bag. If this happens, the patient will need to make a quick trip back to the operating room to put the IOL back at its appropriate axis.
How can you tell if your patient has experienced such a rotation? And how should you manage this situation?
Toric IOLs counteract corneal astigmatism; in the United States the vast majority are manufactured in roughly 0.5 D steps from 1 D to 4 D of cylinder. They depend on good alignment to do their job; one rule of thumb states that for every 10 degrees of misalignment, one-third of the astigmatism-reducing effect is lost. By the time a toric has rotated 45 degrees, all benefits are lost (Lee BS, et al).
Toric IOLs are carefully placed by the surgeon on their intended axis in the capsule. This axis will correspond roughly to the steep axis of the anterior cornea, but because of other sources of cylinder in the eye, especially posterior corneal curvature and expected corneal remodeling after incisional surgery, it will rarely correspond exactly.
We know that, unfortunately, somewhere between 1% and 3% of all torics rotate to some degree after placement. This rotation will always occur within 4 weeks of surgery; after that, the anterior and posterior leaflets of the capsule fuse together and lock down the IOL’s haptics. Because the haptics of all toric IOLs curve counterclockwise out from the optic of the IOL, when they rotate, they rotate clockwise.
The quickest suggestion that a toric IOL has rotated will be your patient’s happiness; they paid a premium price for a lens that should provide good uncorrected vision at one distance, and if they did not get what they were expecting, it is possible that they have suffered a rotation.
The most accurate indication that a toric IOL has rotated is a refraction with a significant amount of astigmatism but a spherical equivalent that is close to the original refractive target, such as emmetropia. Each surgery center will have its own criteria for when the benefits of a toric rotation outweigh the risks, but commonly this will be triggered when the residual astigmatism rises to around 1 D of cylinder and the patient is bothered by the blur.
Some surgery centers will indicate to you at what axis they wanted the toric to be aligned, and you can compare this number to the observed axis in the eye. However, this is the least useful method for evaluating axis: If the patient is unhappy and vision could be improved by a rotation, they will likely be offered this, regardless of the orientation of the IOL.
If you suspect a rotated toric, you must speak with the surgery center as quickly as possible. This is not an emergency, but the surgeon will want to correct the IOL’s axis before it locks down, and the window for an easy rotation is sometimes only 1 month.
Reference:
- Lee BS, et al. Ophthalmology. 2018;doi:10.1016/j.ophtha.2018.02.012.
For more information:
Oliver Kuhn-Wilken, OD, is a staff optometrist at Pacific Cataract and Laser Institute’s Tualatin Clinic in Oregon.
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