title: Evaluation of the validity and reliability of A-scan ultrasound biometry with a single use disposable cover.
abstract: BACKGROUND
  The UK Medical Devices Agency has suggested that ophthalmic practitioners should, where practicable and not compromising clinical outcome, restrict corneal contact devices to single patient use to minimise a remote theoretical risk of transmission of new variant Creutzfeldt-Jakob disease (vCJD). This study reports on a modified technique of ultrasound A-scan biometry that complies with the MDA recommendations.
  
  
  METHODS
  The right eyes of 37 consecutive hospital patients had a series of biometry readings taken with a Humphrey 820 A-scan instrument with a plane wave transducer use d conventionally and with the addition of a disposable latex cover.
  
  
  RESULTS
  Intrasessional repeatability of axial length measurements was similar for conventional readings--mean difference 0.027 mm, 95% confidence intervals (CI) +/- 0.44 mm and those taken with a disposable cover (0.028 mm, CI +/- 0.38). Intersessional repeatability was equivalent with (0.002 mm, CI +.- 0.51) and without a cover (0.03 mm, CI +/- 0.51). Readings with a cover were not significantly different from those without (paired t test; p >0.05), but tended to be greater (mean difference 0.085 mm, CI +/- 0.60).
  
  
  CONCLUSIONS
  These findings suggest that corneal contact biometry with a disposable cover is a viable and theoretically safer alternative to the conventional technique.
authors.affiliation: Department of Optometry and Neuroscience, UMIST, PO Box 88, Manchester M60 1QD, UK. kevin.cass@stud.umist.ac.uk
authors.forename: K
authors.initials: K
authors.lastname: Cass
authors.forename: C M
authors.initials: CM
authors.lastname: Thompson
authors.forename: C
authors.initials: C
authors.lastname: Tromans
authors.forename: I C J
authors.initials: IC
authors.lastname: Wood
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001699:Biometry / Q000295:instrumentation*; D004209:Disposable Equipment / Q000592:standards; D004867:Equipment Design; D006801:Humans; D008875:Middle Aged; D015588:Observer Variation; D009885:Ophthalmology / Q000295:instrumentation*; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000295:instrumentation* / Q000592:standards