Comparative analysis of the effectiveness of various calculation formulas and measurement systems for the target astigmatic axis of the toric IOL in intraocular correction of corneal astigmatism

Background. The effectiveness intraocular correction of corneal astigmatism on the target astigmatic axis in the online calculators toric IOL.

The aim. To establish the effectiveness of corneal astigmatism correction by toric IOLs calculated by various methods of astigmatic axis measurement.

Material and methods. Forty patients (60 eyes) with corneal astigmatism were analyzed. Keratometry parameters for calculations in 30 eyes were obtained using Wave Light Oculyzer II or Pentacam HR, the measurement of the toric astigmatic axis was carried out using the Kane formula. In 30 eyes, keratometric data for calculation were obtained using the Verion Measurement Module, the target axis was calculated using the Barett formula in Verion.

Results. Statistically significantly lower vector and centroid error was shown by calculations of the target astigmatic axis using the Kane formula with Oculyzer II or Pentacam HR keratometry compared with the results of calculations with kerat ometry and Barett in Verion (p < 0.05). The smallest centroid (0.05 dpt) and the smallest average absolute error (0.47 ± 0.51 dpt) of the residual astigmatism indicators in the Kane calculation group, the arithmetic difference of the calculated target axes of the toric orientation according to Verion and Kane revealed, in 70 % of the calculations of the second group, a difference of more than 5° in measuring the axis orientation. The percentage of eyes with a vector error of less than 0.5 dpt in the second group exceeded the indicator of the first group by 13.3 %, less than 1.0 dpt – by 23.3 %.

Conclusion. The calculation of the toric axis according to online formula using Oculyzer II or Pentacam HR keratometric indicators allows us to obtain a smaller average centroid error of 0.05 dpt compared with a centroid error of 0.25 with the orien tation of the toric axis according to keratometric measurements on Verion and the calculation on Verion.

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