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Refractive Surgery/Vision Correction

Consider These Pearls When Treating Posterior Corneal Astigmatism

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Posterior corneal astigmatism (PCA) plays a significant role in total refractive astigmatism, but can still be a confusing topic, observed Elizabeth Yeu, MD, assistant professor, Eastern Virginia Medical School, and partner, Virginia Eye Consultants, during OSN New York 2018.

As many as 13% of patients have with-the-rule astigmatism, noted Dr. Yeu, which can lead to surprise results. If you don’t account for PCA, with-the-rule patients are overcorrected and flip to against-the-rule. Moreover, against-the-rule patients are undercorrected and are left with residual against-the-rule cylinder.

How does PCA behave in patients with oblique corneal astigmatism? Dr. Yeu noted that the answer is unclear, but there are two theories:

  • Oblique astigmatism is actually with-the-rule astigmatism that was captured along its march towards against-the-rule.
  • It is naturally occurring oblique astigmats.

She explained that the patient’s spectacles can clue clinicians in to the refractive astigmatism. For oblique astigmatism, she suggested treating on the spot or choosing higher toric power if spectacles demonstrate a greater amount. 

Finally, Dr. Yeu said that PCA is “not the only sneaky consideration in refractive astigmatism. Effective lens position can drastically affect the strength of toric power, especially in shorter eyes.” Specifically:

  • In < 22.0 mm eyes, consider decreasing toric power.
  • In > 26.0 mm eyes, consider increasing toric power.

Yeu E. Posterior corneal astigmatism: What are the best ways to identify it? Talk presented at: OSN New York 2018; September 28-30, 2018; New York.

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