Comparison of the Biometric Formulas for Applanation A-Scan Ultrasound Biometry

Friday, April 17, 2015
KIOSKS (San Diego Convention Center)
Fatih Ozcura, MD
Serdar Aktas
Haci M. Sagdik
Mehmet Tetikoglu

Purpose
To compare the accuracy in predicting postoperative refraction determined by various biometric formulas using applanation A-scan ultrasound.

Methods
This retrospective study included 485 eyes that had uneventful phacoemulsification with intraocular lens (IOL) implantation. Applanation A-scan ultrasound biometry (Sonomed EZ Scan AB 5500+, Lake Success, NY, USA), and postoperative manifest refraction were obtained in all eyes. Biometric data were entered into each of the 5 IOL power calculation formulas (SRK II, SRK/T, Holladay I, Hoffer Q, and Binkhorst II). All eyes were divided into 3 groups according to axial length: short eyes ≤22.0 mm, average eyes 22.0 to 25.0 mm, and long eyes ≥25.0 mm. Postoperative spherical equivalent calculated and compared to the predicted refractive error with each biometric formula.

Results
The mean absolute error (MAE) of SRK II, SRK/T, Holladay I, Hoffer Q, and Binkhorst II formulas were 0.53±0.44 diopter (D), 0.53±0.44 D, 0.55±0.45 D, 0.57±0.46 D, and 0.61±0.48 D respectively in all eyes. All formulas have significantly low MAE by comparison Binkhorst II formula (P<0.01). SRK II has the lowest MAE in average (0.49±0.40 D) and short (0.67±0.54 D) eyes. SRK/T has the lowest MAE in long (0.61±0.50 D) eyes. SRK II has highest postoperative hyperopic shift in average (46.8%), short (28.1%) and long (48.4%) eyes. Holladay I has highest postoperative myopic shift in average (66.4%) and long (71.0%) eyes. SRK/T has highest postoperative myopic shift in short eyes (80.6%).

Conclusion
SRK II has lowest postoperative MAE in average and short eyes. SRK/T has lowest postoperative MAE in long eyes. SRK II has highest postoperative hyperopic shift in all eyes. Holladay I has highest postoperative myopic shift in average and long eyes. SRK/T has highest postoperative myopic shift in short eyes.