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IOL rotation can treat residual astigmatism after toric lens implantation
A surgeon explains how a toric IOL calculator helps determine if a lens is ideally aligned.
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Rotating the IOL is one way to treat residual astigmatism after toric IOL implantation, rather than exchanging the implant or undertaking laser vision correction, a surgeonsaid at OSN New York 2014.
“The concept here is pretty straightforward,” John Berdahl, MD, said. “The ideal axis of the toric lens is not the same as the actual axis of the toric lens. And it may not be the same as the intended axis of the toric lens where you intended to put it in the first place.”
Berdahl considers residual astigmatism to be a common problem, having seen about 20,000 entries over the last 2 years entered in the Toric Results Analyzer (astigmatismfix.com), a toric IOL calculator developed by Berdahl and David R. Hardten, MD, to “determine if a previously placed toric IOL is ideally aligned,” according to the website.
Example case
In one case, at 1 week postoperatively, a patient had an IOL at 158° with uncorrected vision of 20/70. The patient had 3.5 D of astigmatism with a spherical equivalent near plano, according to the presentation.
Using the Toric Results Calculator, the current refraction, the position of the existing lens in the patient’s eye and the axis of the lens were calculated. The online analyzer calculated taking the astigmatism from 3.5 D to just under 1 D by rotating the lens 28°, Berdahl said.
Technique
After a good manifest refraction is found, the IOL axis and its toricity must be measured. If it is determined that rotating the IOL can adequately neutralize the astigmatism, the spherical equivalent is acceptable, and the IOL can be easily rotated, then the axis can be measured and marked in order to proceed.
Berdahl recommended marking where the toric lens is in addition to where it will be rotated to, not its originally intended degree, “because now I’ve got even better information that includes the posterior corneal curvature and the surgically induced astigmatism,” he said.
In the example case, the current and desired lens locations were marked, and Berdahl then rotated the IOL 28° clockwise from the initial mark.
If more than 1 week has elapsed postoperatively, Berdahl recommended putting viscoelastic behind the IOL to protect the capsular bag. Next, using a Sinskey hook, it must be ensured that the haptic is freed from the posterior capsule and rotated into the desired position. Then the viscoelastic can be removed before tamping the IOL back into the posterior capsule.
Results
After the 28° rotation, the patient’s visual acuity improved to 20/20 uncorrected.
“I believe that if you can rotate the IOL, that’s the best way to do it because now you’ve neutralized corneal astigmatism with the lenticular astigmatism,” Berdahl said.
If the spherical equivalent is inadequate or rotating the IOL does not effectively neutralize the astigmatism, laser vision correction and implant exchange may also treat the residual astigmatism.
There is wide variability in surgically induced astigmatism, according to Berdahl.
“As we’ve been analyzing this data from our website, what we’re finding is about one-third of the time the problem is that the IOL is rotated,” he said. “About one-third of the time the problem is that the preoperative measurements that we took are not adequate, and about one-third of the time it’s a combination of those two things. So it’s a common problem and one we want to get better at.” – by Kristie L. Kahl
For more information:
John Berdahl, MD, can be reached at Vance Thompson Vision, 3101 W. 57th St., Sioux Falls SD, 57108; email: johnberdahl@gmail.com.
Disclosure: Berdahl reports he is a consultant for Alcon, Allergan, Avedro, Bausch + Lomb, ClarVista, Envisia, Glaukos, Omega Ophthalmic and Vittamed.