Modern technologies, techniques improve IOL calculations after laser vision correction
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WAIKOLOA, Hawaii — Swept-source OCT and total keratometry can help improve IOL calculations in patients who have previously undergone laser vision correction, according to a presentation here.
At Hawaiian Eye 2022, Preeya K. Gupta, MD, said there are several reasons why a post-refractive cornea can cause problems when determining which IOL to use.
First, there is a keratometric index of refraction error caused by some calculation techniques.
“1.3375 is used to convert the radius of anterior corneal curvature into diopters,” she said. “The problem is that it assumes a constant ratio of the anterior-posterior corneal curvature, but of course with LASIK, we’re changing the corneal shape.”
Gupta said that eyes with decentered ablations or smaller optical zones are at higher risk for errors in measurement. Typical devices will extrapolate the central corneal curvature from paracentral measurements, so it is important to use topography on these patients to find decentered ablations.
In addition, Gupta said some formulas that use corneal power to predict estimated lens position can underestimate the position in post-LASIK patients who have reduced corneal power.
“Our modern formulas, such as Haigis-L and Barrett True-K, have increased our refractive accuracy,” she said. “When you are running all this data, it is important to choose formulas that have the lowest amount of residual refractive error based on prediction.”
Gupta said swept-source OCT and total keratometry, in addition to modern formulas, can accurately measure the total corneal power, address the errors caused by estimation and improve the accuracy of IOL calculations in post-refractive eyes.
“We can actually measure the true power of a cornea,” she said. “That really has been our Achilles’ heel, not being able to measure the true power of each individual patient, because it’s always different.”
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Gupta PK. How to approach post laser vision correction IOL calculation. Presented at: Hawaiian Eye 2022; Jan. 15-21, 2022; Waikoloa, Hawaii.
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