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P. Rosales, M. Dubbelman, G.L. Van der Heijde, S. Marcos; A Comparison of Crystalline Phakometry Measurements From a Distortion Corrected Scheimpflug Camera and a Purkinje Imaging System (PIS) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):722.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the anterior and posterior crystalline lens radii obtained with a Scheimpflug Camera and a Purkinje Imaging System for a cross–validation of the techniques. Method: Lens radii were measured on 20 eyes (mean age= 25.9±2.9yr; mean refraction= –1.89±2.34D), using both distortion–corrected Scheimpflug (VUMC University Medical Center, Amsterdam) and a PIS (Instituto de Optica, CSIC, Madrid). The Scheimpflug Camera (Topcon SL–45, adapted with a high resolution CCD camera) captures sections of the anterior segment of the eye. Custom software compensates distortions induced by the geometry of the camera (the object– and image plane are tilted) and the refraction from preceding intraocular surfaces. The PIS captures reflections of double LEDs produced by the anterior corneal (PI), and anterior and posterior lens surfaces (PIII , PIV). The heights of PIII and PIV relative to PI, corneal and lens thickness, anterior chamber depth, and lens refractive index (from Scheimpflug images, and for comparison, from Gullstrand model eye) were used to estimate lens radii, using the equivalent mirror theorem and the iterative method. Measurements were performed using the unaccomodated contralateral eye for fixation. Statistical analysis was performed with Welch test (95% CI). Results:Scheimpflug and PIS average anterior lens radii were 11.35 ± 0.94 and 10.98 ± 1.04 mm, respectively. Average posterior lens radii were 6 ± 0.61 and 6.47 ± 0.73mm. Individual differences across techniques ranged from 1.19 to 0.11 mm for the anterior, and 1.74 to 0.08 mm for the posterior lens. Only 3 of 20 eyes showed statistically significant differences for the anterior lens, and 5 for the posterior lens, using biometry data from Scheimpflug imaging, and 5 and 2 respectively using constant data from Gullstrand model. The merit function provides better agreement than the equivalent mirror theorem in all cases. Conclusions: We found a good agreement in the anterior and posterior lens radii measured with a distortion–corrected Scheimpflug camera and a PIS, which provides a cross–validation of these techniques.
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