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