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Reliability of a Single Light Source Purkinjemeter in Pseudophakic Eyes
Edgar Janunts1, Ekaterina Chashchina, Berthold Seitz
1*PhD †MD ‡MD, PhD Institute of Experimental Ophthalmology, Saarland University, Homburg/Saar, Germany (EJ, EC, AL); Department of Ophthalmology, Saarland University Medical Center, Homburg/Saar, Germany (EC, BS); and Section of Neurobiology of the Eye, Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany (FS).
Purpose:
To study the reliability of Purkinje image analysis for assessment of intraocular lens tilt and decentration in pseudophakic eyes.
Methods:
The study comprised 64 eyes of 39 patients. All eyes underwent phacoemulsification with intraocular lens implanted in the capsular bag. Lens decentration and tilt were measured multiple times by an infrared Purkinjemeter. A total of 396 measurements were performed 1 week and 1 month postoperatively. Lens tilt (Tx, Ty) and decentration (Dx, Dy) in horizontal and vertical directions, respectively, were calculated by dedicated software based on regression analysis for each measurement using only four images, and afterward, the data were averaged (mean values, MV) for repeated sequence of measurements. New software was designed by us for recalculating lens misalignment parameters offline, using a complete set of Purkinje images obtained through the repeated measurements (9 to 15 Purkinje images) (recalculated values, MV'). MV and MV' were compared using SPSS statistical software package.
Results:
MV and MV' were found to be highly correlated for the Tx and Ty parameters (R2 > 0.9; p < 0.001), moderately correlated for the Dx parameter (R2 > 0.7; p < 0.001), and weakly correlated for the Dy parameter (R2 = 0.23; p < 0.05). Reliability was high (Cronbach α > 0.9) for all measured parameters. Standard deviation values were 0.86 ± 0.69 degrees, 0.72 ± 0.65 degrees, 0.04 ± 0.05 mm, and 0.23 ± 0.34 mm for Tx, Ty, Dx, and Dy, respectively.
Conclusions:
The Purkinjemeter demonstrated high reliability and reproducibility for lens misalignment parameters. To further improve reliability, we recommend capturing at least six Purkinje images instead of three.
