Evaluation of the validity and reliability of A-scan ultrasound biometry with a single use disposable cover.
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.
Cass
K
K
Department of Optometry and Neuroscience, UMIST, PO Box 88, Manchester M60 1QD, UK. kevin.cass@stud.umist.ac.uk
Thompson
C M
CM
Tromans
C
C
Wood
I C J
IC
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