Comparison of Noncontact Specular and Confocal Microscopy for Evaluation of Corneal Endothelium
Purpose
To compare endothelial cell assessments obtained by non-contact specular and confocal microscopy using the Konan NSP-9900 and Nidek ConfoScan4 systems.
Methods
Sixty-four healthy eyes and 127 diseased eyes (49 eyes with Fuchs’ Endothelial Dystrophy and 78 with glaucoma) were examined with the Nidek ConfoScan4 confocal microscope and the Konan NSP-9900 specular microscope. Certificated anterior segment graders at the Doheny image reading center compared the images from both instruments side by side for image quality assessment. Endothelial cell density (ECD) measurements were calculated with each instrument’s fully automated, semi-automatic and manual methods, and compared to each other.
Results
All normal and most of glaucomatous eyes had gradable images. However, in corneas with Fuchs’ Endothelial Dystrophy, poor image quality precluded ECD grading in 8.2% (4/49) and 40.8% (20/49) of the eyes, as obtained by confocal and specular microscopy respectively. Regardless of whether the eye was normal or glaucomatous, ECD values obtained manually from either device were not statistically significantly different (P>0.05). In contrast, machine-generated ECD values were significantly different from manual results, measuring greater in all cases with specular microscopy. Machine-generated ECD values from confocal microscopy also differed significantly from manual determinations, but not in a consistent direction. Semi-automatic methods of both instrument obtained clinical acceptable ECD values.
Conclusion
Automatic machine-generated ECD measurements differed significantly from manual assessments, suggesting the automated results should be used with caution. ECD values derived from Konan Center method were comparable to Nidek’s Manual method in both normal and glaucomatous eyes, suggesting that, with manual grading, the two instruments can be used interchangeably for reliable ECD measurements. Because of higher proportion of gradable images, confocal microscopy might be superior to specular microscopy for ECD measurements in Fuch’s Corneal Dystrophy.