Comparison of Recording Systems and Analysis Methods in Specular Microscopy

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Abstract
To compare corneal endothelial cell images from contact and automated noncontact specular microscopes and to compare endothelial image analysis by the Konan Robo Center Method and the Bio Optics Bambi Corners Method. Twenty-six normal corneas of 13 subjects and 41 penetrating keratoplasties (PKs) of 38 patients were photographed with a Keeler-Konan contact specular microscope and a Konan Noncon Robo automated noncontact specular microscope. (i) After measuring and calibrating the magnification of each instrument, we digitized the cellular apices and analyzed the images from both instruments by using the Corners Method modified to accept x and y calibrations, (ii) Using the internal calibration marks of the Konan Noncon Robo specular microscope for calibration of magnification (as required for the Center Method), we evaluated identical cells on images from this microscope by both the Center Method and the Corners Method. (iii) We evaluated the reproducibilily of both methods by repeating measurements on the same image. (i) When the images were properly calibrated for magnification by using an external scale, endothelial cell density (ECD) of normal corneas was 2,703 ± 354 (mean ± SD) cells/mm2 by contact and 2,685 ± 357 cells/mm2 by noncontact techniques (p = 0.51). ECD of PK corneas was 1,767 ± 773 cells/mm2 by contact and 1,807 ± 775 cells/mm2 by noncontact techniques (p = 0.31). (ii) When images from the Konan Noncon Robo specular microscope were calibrated for magnification on the internat marks, the measured ECD from the same noncontact photographs was 6% less (p 2 (i) Images from the automated noncontact specular microscope may be used interchangeably with those from the contact specular microscope to measure ECD, but only if both are properly calibrated by measuring an external scale. (ii) As a method of analysis, the Center Method is equivalent to the Corners Method in normal corneas, but the proprietary internal calibration of the Center Method, which is required for its use, yields ECDs −6% less than when an external scale is used for distance calibration. (iii) Cell density measurements by both the Center Method and the Corners Method were reproducible within 1%.

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