ASSESSMENT OF A NEW THROUGH-THE-EYELID TECHNIQUE FOR A-SCAN ULTRASOUND OCULAR AXIAL LENGTH MEASUREMENT

This study evaluated the repeatability both within one session and bet ween two sessions of a new technique of axial length measurement using 'A' scan ultrasound through the eyelids. The validity of the techniqu e was assessed by comparing the results to those taken through the cor nea, The new technique was very reliable, the mean difference between two readings at the first visit being 0.01 mm and between the two visi ts being 0.01 mm with 95% of differences between two readings in both cases being less than two standard deviations. The axial length measur ements through the lid were a mean of 0.05 mm longer than the corneal measurements. The standard deviation of the difference between the two forms of measurement was 0.16 mm and 95% of axial length readings thr ough the eyelid were within two standard deviations (+/-=0.32 mm) of t he corneal measurement. Providing strict criteria are applied to the q uality of the 'A' scan images we believe that satisfactory axial lengt h values may be obtained using this technique. (C) 1998 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved.