Comparison of A-scan and MRI for the measurement of axial length in silicone oil-filled eyes.
ABSTRACT The aim of the study was to compare the accuracy of A-scan biometry and MRI for the measurement of axial length in silicone oil-filled eyes.
This was a prospective randomised study of 70 patients. Biometry was performed using MRI in 33 patients (MRI group) and A-scan echography in 37 patients (A-scan group). The difference between predicted and final refraction was measured and evaluated statistically.
In patients with axial length >/=26 mm, the mean deviation of the final from predicted refraction was -1.23 (SD 0.67) D in the MRI group and -2.3 (SD 2.02) D in the A-scan group. The difference between these two groups was statistically significant (p = 0.02). In patients with axial length <26 mm, the mean deviation of the final from predicted refraction was -0.12 (SD 1.29) D in the MRI group and -0.33 (SD 1.39) D in the A-scan group. There was no statistical significance between the two groups (p = 0.629).
For highly myopic patients MRI biometry was a more accurate measurement of axial length in silicone oil-filled eyes. A-scan and MRI biometry were comparably accurate in measuring axial length in patients with axial length <26 mm.
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ABSTRACT: In this paper, we suggest a new approach for accurate measurement of three-dimensional eye movements employing dual- camera acquisition. Two calibrated mini CCD cameras are used to capture two simultaneous images of one eye. Center-of-mass and template-matching algorithms are utilized to obtain two-dimensional coordinates of the center of pupil and iris striation. Instead of asking each subject to fulfill intricate calibration steps, a novel and simpler technique to solve geometric distortion is presented by utilizing direct linear transformation (DLT) algorithm which requires only one preliminary calibration procedure for each camera without changing any camera installation. The DLT algorithm is then used to extract three-dimensional coordinates of the center of the pupil and iris striation from prior two-dimensional coordinates, allowing the three-dimensional angular positions of the eye to be computed. Real-time eyeball visualization based on tracking results is incorporated to help clinicians diagnose eye movements. Experimental results show that our system has high accuracy, as the average errors in the horizontal, vertical, and torsional angular positions were confined to 0.15◦, 0.14◦, and 0.20◦, respectively. Real-time implementation demonstrates that our system can be used in clinical routines to observe either voluntary or involuntary human eye movements.IEEJ Transactions on Electrical and Electronic Engineering 01/2013; 8(3):238-246. · 0.36 Impact Factor