Toric IOL prediction

Toric IOL outcomes

Comparative study seeks highest prediction accuracy. Cheryl Guttman Krader reports

Toric IOL prediction accuracy varies significantly depending on the tool used to measure corneal astigmatism, reported Qayim Kaba at the 37th Congress of the ESCRS in Paris, France.

He presented results from a prospective cohort study that showed the corneal astigmatism prediction error differed whether the keratometry data used for toric IOL calculations was acquired with the OPD (Nidek), Pentacam (Oculus) or IOLMaster (Carl Zeiss Meditec). Overall, Pentacam topography resulted in the least corneal astigmatism prediction error.

“Keratometry values from these three modalities may be used for toric IOL calculations to determine the most suitable lens for correcting astigmatism, but to our knowledge, no study has compared the accuracy of their predictions,” said Mr Kaba, a medical student in the United Kingdom, presenting the research conducted at Uptown Eye Specialists, Canada.

The investigation included 42 eyes of Figure 1. POM3 WTR results by mean centroid error of prediction error for each modality.

Figure 2. POM 3 ATR results by mean centroid error of prediction error for each modality.

Figure 3. POM3 Oblique results by mean centroid error of prediction error for each modality.

26 patients that had reliable topography measurements and no ocular comorbidities. Postoperative residual astigmatism was determined using vector analysis. Comparisons between modalities were based on the centroid astigmatism prediction error and with eyes categorised by type of astigmatism. Astigmatism was with-therule (WTR) in 13 eyes, against-the-rule (ATR) in 23 eyes and oblique in six eyes.

Postoperative three-month results showed the centroid error of prediction error in WTR eyes was greatest using keratometry data from the IOLMaster (0.23D@150°) and not significantly different comparing the Pentacam (0.12D@128°) and OPD (0.11D@60°). In the eyes with ATR astigmatism, the centroid error of prediction error was lowest for the Pentacam (0.04D@169°) and not significantly different between the IOLMaster and OPD (0.08D@54° and 0.09D@34°, respectively). In the cohort with oblique astigmatism, the centroid error of prediction error was identical using the Pentacam and OPD keratometry values (0.02D @148°) and significantly greater using the IOLMaster (0.13D@142°).

An axis-to-axis comparison was also done, and the analyses showed no statistically significant difference for actual and predicted axis comparison between the IOLMaster, Pentacam and OPD.

TOPICS FOR FUTURE RESEARCH Mr Kaba noted that the prediction accuracy using the optical biometer for measuring the cornea might be improved using the newer IOLMaster 700, which differs from the IOLMaster in that it incorporates the posterior cornea to calculate total keratometry. He also noted that the current APACRS toric IOL calculator allows surgeons to input keratometry data from different modalities which can generate a value for use in the power calculation.

“It would be interesting to see if these methods result in higher prediction accuracy for toric lenses,” he said. Qayim Kaba: qayimkaba@gmail.com

INDIA