Abstract

P 300

Axial eye length determination by contact B-Scan sonography

Philipp Martius, Stefanie Tech, Oliver Stachs, Rudolf F. Guthoff
Universitäts-Augenklinik Rostock

Objective
The therapy of Microphthalmus or the differentiation of an Exophthalmus to a Pseudoexophthalmus needs a determination of the axial eye length. Coupling problems avoid its correct determination based on contact B-scan sonography. The aim of the study is the development of a simple method for the determination of the axial eye length based on this contact B-scan sonography.
Methods
For method development the ultrasound devices Master Vu (Sonomed Inc.), CineScan (Quantel Medical) and I³ System-ABD (Innovative Imaging Inc.) were used. For defining the position of the coupling layer of the handpiece and the correlation to the B-scan video display a fiber phantom was measured by the different ultrasonic devices. In a first step an axial B-scan in immersions technique of one subject was recorded. A strong signal of the posterior lens pole and the ocular fundus as well as the visibility of the cornea was required. In a second step an axial B-scan of the same subject was generated in contact mode with the closed eyelid. For the estimation of the eyelid thickness an axial length measurement was effected under consideration of the device-specific coupling layer position of the different handpieces and the measured eye length using immersions technique. Out of it device-specific correction values result. For the evaluation of the method the axial eye length of 30 eyes (10 each with myopia, emmetropia and hyperopia) based on contact B-scan sonography was compared with the optical biometry (IOL Master).
Results
Using the device-specific correction values (Master Vu 3.0 mm), (CineScan 1.5 mm) und (System-ABD 1.5 mm) it is possible to determine the absolute eye length of patients. In comparison with the optical biometry of the so far tested subjects the CineScan-device denoted the highest difference of 1.0 ± 0.5 mm. The Sonomed Inc. pointed a difference of 0.3 ± 0.3 mm and the difference of the I³ System-ABD-device was 0.4 ± 0.3 mm.
Conclusions
The developed method is able to determine the axial eye length in vivo by contact B-scan sonography without immersions technique. This offers the possibility to differentiate an Exophthalmus of a Pseudoexophthalmus or a determination of the axial eye length for Microphthalmus patients.

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