Improving IOL power calculations

February 14, 2007

By using calibrated axial length readings obtained with partial optical coherence interferometry (PCI) and intraocular lens (IOL) power calculation formulas incorporating anterior chamber depth (ACD) prediction algorithms, the accuracy of power calculations can be greatly improved, according to study published in the February issue of Acta Ophthalmologica Scandinavia.

By using calibrated axial length readings obtained with partial optical coherence interferometry (PCI) and intraocular lens (IOL) power calculation formulas incorporating anterior chamber depth (ACD) prediction algorithms, the accuracy of power calculations can be greatly improved, according to study published in the February issue of Acta Ophthalmologica Scandinavia.

Thomas Olsen from the University Eye Clinic, Aarhus Kommunehospital, Aarhus, Denmark, calculated the IOL power for 461 consecutive cataract patients using both PCI and ultrasound. The accuracy of the results from each technique were compared. Predictions were calculated using both a recently published 5–variable method and the Haigis 2–variable method. All calculations were optimized in retrospect to account for systematic errors, including IOL constants and other off–set errors.

The average absolute IOL prediction error (observed minus expected refraction) was 0.65 D with ultrasound and 0.43 D with PCI using 5–variable ACD prediction method (p‹0.00001). The number of predictions within ±0.5 D, ±1.0 D and ±2.0 D of the expected outcome was 62.5%, 92.4% and 99.9% with PCI, compared with 45.5%, 77.3% and 98.4% with ultrasound (p‹0.00001), respectively. The 2–variable ACD method resulted in an average error in PCI prediction of 0.46 D, which was found to be significantly higher than the 5–variable method (p‹0.001).

Olsen concluded that the accuracy of IOL power calculations is significantly improved when using PCI and modern calculation formulas that incorporate the latest generation ACD prediction algorithms.