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Effect of Axial Length Measurement Method on Refractive Outcomes of Cataract Surgery: Real World Comparison of Partial Coherence Interferometry and Immersion Ultrasound. Nathaniel Knox Cartwright & Derek Tole Bristol Eye Hospital, Bristol, United Kingdom Financial Disclosure: none. Background.
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Effect of Axial Length Measurement Method on Refractive Outcomes of Cataract Surgery:Real World Comparison of Partial Coherence Interferometry and Immersion Ultrasound. Nathaniel Knox Cartwright & Derek Tole Bristol Eye Hospital, Bristol, United Kingdom Financial Disclosure: none
Background • Partial coherence interferometry (PCI) has become the clinical gold standard for axial length (AL) measurement but cannot be used in all eyes • Intraindividual comparisons of PCI and immersion ultrasound (IUS) have found they result in postoperative refractive equivalence after cataract surgery • This contrasts with the clinical situation for PCI users who only use IUS as a second line measurement method • The purpose of this study was to compare refractive outcomes after cataract surgery when PCI is used for AL measurement with when IUS is used due to PCI failure
Cohort • 2544 phacoemulsification and Akreos Adapt AO (Bausch & Lomb) IOL implantations • No copathology • Uncombined and uncomplicated surgery • Postoperative subjective refraction • Corrected distance visual acuity ≥6/12 (20/40) • IOLMaster (software version 3, Carl Zeiss Meditec) keratometry performed in all • PCI AL measurement attempted in all but IUS used if this was not possible
Optimisation Process • Hoffer Q, Holladay 1 and SRK/T formulae entered in code into Freemat (http://freemat.sourceforge.net/) • Optimised biometry formula constants calculated by 2 methods • To give an overall mean deviation from predicted postoperative refraction of zero (zero method) • As recommended in the IOLMaster manual, that is as the mean of the all personalised constants excluding those > 2 SD from overall mean (Zeiss method)1 1. IOL Master Software Version 3.xx User Manual.http://www.doctor-hill.com/iol-master/docs/iolmaster_3.pdf (downloaded 17/0/2008).
Results: Zero method Unpaired t-test: PCI V IUS all p>0.05
Results: Zeiss method Unpaired t-test: PCI V IUS all p<0.05
Zeiss method Zero method
Conclusions • Optimised biometry formula constants (BFC) varied according the method by which they were calculated • When the Zeiss optimisation method was used, AL measurement by IUS following PCI measurement failure did not require use of different BFC and did not worsen refractive outcomes • Additionally, the Zeiss optimisation method resulted in a lower mean absolute error than when the zero method is used