1. ¹Department of Optometry and Ophthalmic Dispensing Anglia Polytechnic University, Cambridge, UK
2. ²Department of Ophthalmology Norfolk and Norwich University Hospital NHS Trust, Norwich, UK

Correspondence: P Gunvant, Department of Optometry and Ophthalmic Dispensing Anglia Polytechnic University, East Road, Cambridge, CB1 1PT, UK. Tel: +44 1223 363271 x 2684; Fax: +44 1223 417712; E-mail: contact@pinakin-gunvant.com

Received 8 July 2002; Accepted 17 December 2002.

Abstract

Purpose To evaluate the interobserver and intraobserver reliability of a commercially available, portable, ultrasonic pachymeter.

Methods For the interobserver variability study, 42 healthy subjects underwent repeated ultrasonic pachymetry under topical anaesthesia performed by two observers. For the intraobserver study, another 30 further healthy subjects underwent repeated pachymetry by one of the observers. Agreement was analysed by means of Bland–Altman plots and by determination of the intraclass correlation coefficient.

Results For the interobserver variability study, the mean measurement difference between observers was 0.7 m (95% CI -0.8–2.2 m) and the intraclass correlation coefficient was 0.9958 (95% CI 0.9922–0.9977). The Bland–Altman plot showed narrow limits of agreement with respect to central corneal thickness (CCT). For the intraobserver variability study, the mean difference between the repeated measurements was 0.9 m (95% CI -3.1–1.3 m). The intraclass correlation coefficient was 0.9934 (95% CI 0.9863–0.9969). A Bland–Altman plot again showed narrow limits of agreement with respect to CCT. The mean CCT for 72 subjects was 538 m (95% CI 528–545 m).

Conclusions Measurements of CCT using the BVI Pocket Pachymeter were repeatable and had excellent interobserver reliability. Measurement variation amounted to less than 0.2% assuming a mean CCT of 538 m.