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The contact and immersion ultrasound methods compared using the ray tracing method

Falhar M., Rehak J.

Optica Applicata

2010

Vol. 40, nr 1

77--92

The goal of this article was to compare the contact and immersion ultrasound methods using simulated data. The pursued changes were interrelated with both the axial length of the eye and with partial biometry parameters. The results were compared with empirical data from real eye samples. The main analysing method was a modified algorithm for the ray tracing method created in the DELPHI programming environment (Borland Enterprise). The sample included 129 eyes (64% women and 36% men) of average age 73.65 (SD 9.33) scheduled for surgical removal of cataract. The average axial length was 23.12 mm (SD 1.31). The methods were compared using the simulated movement of the probe from central and coincident positions. We confirmed the tendency of the contact method to register more scattered beam which provides distorted biometric data from the periphery. This was verified by the real data analysis. The average axial length of the eye was 23.12 mm (SD 1.315), measured by the contact method and 23.26 mm (SD 1.298), measured by the immersion method. The difference between the methods was 0.145 mm. The most important changes occur in the vitreum depth which correlated with the total axial length (r = 0.89). The ray tracing method provided evidence of greater accuracy of the immersion method which was more sensitive to probe displacement and provided more accurate data. The axial length of the eye was longer according to the immersion method but this had only secondary influence on the accuracy of the method. Applanation of the cornea is the primary source of the contact method inaccuracy. The vitreum depth was the most influenced.

A theoretical model of the human eye based on ultrasound and corneal data

Falhar M., Rehak J.

Optica Applicata

2009

Vol. 39, nr 1

195--210

The purpose of this study was to create a theoretical model of the eye based on a comparison of the real spherical equivalent of the eye and the calculated value of the axial refraction. The main contribution of this model is that it enables calculation of the equatorial plane of the lens for accurate assessment of the IOL position for a spherical eye model. The Gullstrand model of the eye was used as the source eye model and this was modified for the purposes of this study. The axial refraction of the final model of the eye was compared with the spherical equivalent. The accuracy of the developed model was statistically confirmed using statistic tests. Individual calculation of the axial refraction using it shows that IOL calculation is possible without any general statistical presumptions. It permits the calculation of variables with an accuracy accepted by inferential statistics. The accuracy of this theoretical eye model however, is limited by extreme values of variables - an extreme value provides a less accurate result.