Official ESCRS | European Society of Cataract & Refractive Surgeons


Comparative efficacy of Barrett True-K IOL power calculation with and without measured posterior corneal astigmatism

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Session Details

Session Title: Toric IOLs & Lens Power Calculations

Session Date/Time: Sunday 15/09/2019 | 08:00-10:00

Paper Time: 09:14

Venue: Free Paper Forum: Podium 3

First Author: : M.Lawless AUSTRALIA

Co Author(s): :    C. Hodge   G. Sutton   T. Roberts   C. Chan                    

Abstract Details


Utilizing posterior corneal data may increase the accuracy of IOL calculations. The Barrett IOL power calculation formulae have recently incorporated the option to include the measured posterior corneal astigmatism (PCA). In this study of eyes which have previously had corneal laser surgery, we compare refractive outcomes using the Barrett True-K formula with and without PCA values to determine the impact upon the refractive success following surgery.


Private clinic, Sydney Australia


Patients with successful cataract surgery following previous corneal laser refractive procedures were identified. Using the values obtained from the IOLMaster 700 and the revised Barrett True-K formula, the refractive target was identified. The difference from the postoperative spherical equivalent was then calculated to achieve the arithmetic and absolute difference from target. Calculations were grouped by patients with and without pre-refractive history and with and without PCA.


There were 16 eyes with prior refractive history and 22 eyes that were calculated without prior information. The mean absolute error (MAE) for patients with refractive history was 0.36±0.22D and 0.30±0.22D for True K and True K with PCA values respectively (75.0% and 81.25% were within ± 0.5D of target). For patients without prior refractive history, the MAE was 0.38±0.37D and 0.37±0.32D for True K and True K with PCA respectively (72.7% and 68.2% were within ± 0.5D of target).


Post corneal laser refractive patients represent a challenge for surgeons when choosing the IOL power. Our cohort suggests that obtaining the refraction history may provide additional accuracy compared to no-history calculations. The incorporation of PCA into the Barrett True K formula represents an additional positive contributive factor to increase postoperative accuracy.

Financial Disclosure:


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