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Darshak S Patel, Luca Ilari; Comparison of refractive outcomes for different intraocular lens formulae using ultrasound biometry. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1152.
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© ARVO (1962-2015); The Authors (2016-present)
Applanation A-scan ultrasound biometry (USB) remains widely used, particularly when partial coherence interferometry (PCI) devices fail to penetrate the cataract, or if there is poor fixation. This retrospective study investigates a large cohort of phacoemulsification plus intraocular lens (IOL) cases employing USB and the effect of both axial length and IOL formula choice on refractive outcomes.
We examined all phacoemulsification plus IOL cases using USB, across two years. The exclusion criteria were combined procedures, posterior capsule rupture, failure to achieve intracapsular IOL placement and previous corneal refractive surgery. All cases had axial lengths (AL) calculated from the Nidek US-1800 Echoscan. Keratometry was PCI (IOL Master 500) derived. Cases were subdivided into 3 groups based on USB derived axial length: short (<22.0 mm), medium (22.0-26.0 mm) and long (>26mm). All cases were performed by a consultant surgeon using the Raynor C-flex Aspheric or Superflex Aspheric IOLs. Post-operative autorefraction was recorded for each case. The predicated post-operative spherical equivalent derived from Hoffer Q, Holladay 1 and SRK/T formulae was compared to the actual post-operative spherical equivalent using the Medisoft electronic record system.
Following exclusions, 181 consecutive cases were identified for analysis. There were 17 short, 153 medium and 11 long axial length eyes. The ages ranged from 37 to 96 years old with a mean of 72.41 years. For short ALs, a significant hypermetropic shift was seen with all three formulae; the lowest median arithmetic error (MAE) was obtained with Hoffer Q (+0.40 ± 1.01 dioptres). For medium and long ALs, SRK/T produced the lowest MAE (-0.02 ±0.91 dioptres and +0.07 ±0.73 dioptres, respectively).
For short eyes, USB can be inaccurate and care should be taken to eliminate sources of measurement error. Even with the use of the Hoffer Q formula, a post-operative hypermetropic shift should be anticipated. This study supports the routine use of SRK/T with medium and long ALs derived from USB.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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