Prediction of refractive outcomes with toric intraocular lens implantation

Abstract

Prediction of astigmatic outcomes with toric IOLs can be improved with appropriate measuring devices and methods to establish the required toric IOL power.

New regression formula for toric intraocular lens calculations

“…One cause of this untoward occurrence is inaccurate estimation of the total corneal astigmatism. 6,9,[11][12][13] A perfect method to calculate preoperative total corneal astigmatism has not been established. 25 To our knowledge, none of the manufacturers' online toric IOL calculators account for posterior corneal astigmatism, 6 resulting in ATR prediction errors when using radii measurements based on the anterior corneal surface alone.…”

“…25 To our knowledge, none of the manufacturers' online toric IOL calculators account for posterior corneal astigmatism, 6 resulting in ATR prediction errors when using radii measurements based on the anterior corneal surface alone. 12,13 The Barrett toric calculator, A which uses a mathematic model to estimate posterior corneal astigmatism, was shown to be better than standard toric calculators that use anterior cornea-based keratometry 12 and those that use direct measurements of the posterior cornea by the Scheimpflug camera device (Pentacam, Oculus Optikger€ ate GmbH). 26 The aim of our present study was to describe a new regression formula (Abulafia-Koch) that calculates an estimated net corneal astigmatism using standard K measurements (based on the anterior cornea).…”

“…[1][2][3][4] However, the results are not always predictable. 3,5,6 Corneal surgically induced astigmatism (SIA), 2,7 errors in the alignment of toric IOLs, 8 errors in measuring corneal astigmatism, [9][10][11][12] and errors in the method used to predict the required toric IOL and residual astigmatism after surgery 12,13 have been described as factors that might contribute to unexpected residual astigmatism. Accurate measurement of net corneal astigmatism in cataract patients is crucial to achieve optimum postoperative uncorrected visual acuity and patient satisfaction.…”

“…Those methods apply nomograms, 13 coefficients of adjustment, 6 direct measurements of the posterior cornea, 10,18 a ray-tracing approach using combined keratometry and tomography data, 14 intraoperative aberrometry, 19 and mathematic models. 12 The purpose of this study was to describe a new regression formula that can calculate the estimated total corneal astigmatism using standard keratometry (K) measurements and to compare the error in the predicted residual astigmatism of 2 representative toric IOL calculators with and without the use of the new formula. Those results were further compared with those of the Barrett toric calculator.…”

Progress in Modern Cataract Surgery – New Steps and Algorithms for Precise Measuring and Intraocular-lens Calculations

“…First studies have shown promising outcomes, but further clinical investigation is needed. 34,35 In large sample studies, 34,35 the latest formulae such as Barrett toric, 25 have shown the smallest MAE, and most patients are within the expected post-operative refraction. However, there are still outliers where posterior corneal surface has an influence not present in nomograms.…”