title: Precision of biometry, keratometry, and refractive measurements with a partial coherence interferometry-keratometry device.
abstract: OBJECTIVE
  To evaluate the precision of the axial length (AL), keratometry (K), anterior chamber depth (ACD), astigmatism, and minus astigmatic cylinder axis measurements by a partial coherence interferometry (PCI)-keratometry device.
  
  
  METHODS
  Private practice, Lynwood, California.
  
  
  METHODS
  This prospective comparative observational study analyzed measurements in the second eye to have cataract surgery. Before surgery in the first eye, AL, K, ACD, astigmatism, and cylinder axis in both eyes were measured with an IOLMaster PCI device. The measurements were repeated approximately 1 month later, before second eye-surgery. The 2 sets of measurements were compared.
  
  
  RESULTS
  The study evaluated 121 eyes of 121 patients. The interclass correlation coefficient (ICC) for AL was 0.999 in all 3 signal-to-noise ratio (SNR) categories; the highest difference range was with an SNR below 100. Astigmatism, K, and cylinder axis had a high correlation in flat corneas (K reading <42.0 diopters [D]) (ICC = 0.994, 0.978, and 0.918, respectively) and a poorer correlation with K readings between 42.0 D and 44.0 D (ICC = 0.905, 0.774, and 0.456, respectively) and K readings above 44.0 D (ICC = 0.988, 0.729 and 0.446, respectively).
  
  
  CONCLUSIONS
  The precision of the PCI measurements was extremely high for AL with low fluctuations (95% limits of agreement [LoA], 0.06 mm) and was relatively high for K readings with higher fluctuations (95% LoA, 0.55 D) and for ACD (95% LoA, 0.2 mm). The precision of astigmatism and cylinder axis was high in flat corneas and relatively low in steeper corneas.
authors.affiliation: Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA. jshammas@shammaseye.com
authors.forename: H John
authors.initials: HJ
authors.lastname: Shammas
authors.forename: Steven
authors.initials: S
authors.lastname: Chan
mesh_terms: D000867:Anterior Chamber / Q000473:pathology*; D001251:Astigmatism / Q000175:diagnosis*; D001699:Biometry / Q000379:methods*; D003315:Cornea / Q000473:pathology*; D005123:Eye / Q000473:pathology*; D006801:Humans; D007368:Interferometry / Q000295:instrumentation* / Q000379:methods; D007910:Lenses, Intraocular; D008027:Light; D011446:Prospective Studies; D012029:Refraction, Ocular; D015203:Reproducibility of Results