Astigmatism Prediction Accuracy Of Holladay Equivalent Keratometry Readings In Toric Intraocular Lens Power Calculations.

Residual astigmatism following cataract surgery remains a major factor limiting post operative refraction. The precision of astigmatic predictions is dependent on reliable keratometry measurements. Holladay’s equivalent keratometry reading (EKR65) has been known to be a more stable keratometry reading involving anterior and posterior corneal measurements. This study evaluated the accuracy of using Scheimpflug-derived EKR65 values for intraocular lens (IOL) Toric calculation using the Barrett Toric Calculator compared with the Barrett’s simulated Keratometry (SimK).

The Ottawa Eye Institute, Ottawa, Canada

In this retrospective study; 86 eyes of 68 patients undergoing cataract surgery with Toric IOL implantation (Acrysof IQ SN6AT/SA6AT Toric, Alcon, USA; or Tecnis Toric ZCT IOL, Johnson & Johnson Vision, USA) were included. Estimated residual astigmatism was calculated using Barrett Toric Calculator with keratometry data from EKR65 and SimK. Predicted values by each calculation method was compared with 3 months post-operative manifest refractive astigmatism. Prediction error in residual astigmatism was calculated using Alpins vector analysis method.

The final analysis included eyes with normal corneal topography and average keratometry value (44.9± 0.4 D) and comparable EKR65 readings (44.8± 0.4 D). The mean spherical equivalent at 3 months post-operatively was -0.55± 0.20 D. The SimK yielded a lower mean predictive error vector 0.39±0.07D; compared to the EKR65 (0.42± 0.08D). However, the difference between the two methods was not statistically significant (P=0.93).

The use of Holladay EKR65 for IOL calculations showed comparable astigmatism prediction performance compared to Barrett’s simK when using the Barrett Toric IOL Calculator in normal corneas. Future studies will focus on EKR65 use in Toric IOL calculation for irregular corneas.