title: B-mode-guided vector-A-mode versus A-mode biometry to determine axial length and intraocular lens power.
abstract: OBJECTIVE
  To compare prospectively the reproducibility and accuracy of B-mode-guided biometry with those of A-scan biometry using a conventional A-mode probe to calculate intraocular lens (IOL) power.
  
  
  METHODS
  Department of Ophthalmology, Hôtel-Dieu de Paris, France.
  
  
  METHODS
  The axial length (AL) in 87 eyes of 72 candidates for cataract surgery was determined by B-mode-guided vector-A-mode and A-mode biometry using an Ophthascan S Ultrasound imager. Patients were assigned to one of two groups based on the B-mode biometry: nonmyopic (AL < 24.5 mm; n = 54) or myopic (AL > 24.5 mm; n = 33). Postoperative refractive results were compared with attempted values.
  
  
  RESULTS
  Mean AL variance was significantly greater when using the A-mode than the B-mode: 0.157 mm +/- 0.260 (SD) versus 0.015 +/- 0.018 mm in the myopic group (P < .001) and 0.024 +/- 0.024 +/- 0.045 versus 0.009 +/- 0.011 mm in the nonmyopic group (P < .001). More eyes having B-mode biometry achieved a final refraction within +/- 0.50 diopter (D) of the attempted refraction (63 and 43%, respectively; P < .05). No deviation greater than 1.60 D was observed with the B-mode in the myopic or nonmyopic group. Three cases with a such a deviation (up to 2.24 D) would have been observed had A-mode-based biometry been chosen for the IOL power calculation. In the myopic group, attempted postoperative refraction was within +/- 0.50 D in 78% of eyes having B-mode biometry compared with 65% having A-mode. This difference was not statistically significant. CONCLUSION> These results suggest that the reproducibility and accuracy of AL measurements are significantly better with B-mode-guided A-mode biometry than with A-mode biometry in myopic and nonmyopic eyes.
authors.affiliation: Department of Medical Imaging, Fondation Ophthalmologique A. de Rothshild, Paris, France.
authors.forename: O
authors.initials: O
authors.lastname: Bergès
authors.forename: M
authors.initials: M
authors.lastname: Puech
authors.forename: M
authors.initials: M
authors.lastname: Assouline
authors.forename: L
authors.initials: L
authors.lastname: Letenneur
authors.forename: M
authors.initials: M
authors.lastname: Gastellu-Etchegorry
mesh_terms: D001699:Biometry / Q000379:methods*; D005123:Eye / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006801:Humans; D007910:Lenses, Intraocular; D009216:Myopia / Q000150:complications / Q000000981:diagnostic imaging; D055095:Optics and Photonics; D018918:Phacoemulsification; D011446:Prospective Studies; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D014463:Ultrasonography