Evaluation of the validity and reliability of A-scan ultrasound biometry with a single use disposable cover

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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.

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