Karl Jensen

University of Wisconsin, Madison, Madison, MS, United States

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Publications (4)8.93 Total impact

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    ABSTRACT: To assess the consistency of digitization of 35-mm slides as practiced in ophthalmologic research and estimate the impact of variation on semi-automated retinal vessel width measurements. A single retina slide was repeatedly digitized under various conditions on three scanner models. Average color levels were extracted from the resulting images, from which vessel widths were graded. The color channel level variations and possible correlation with width were analyzed. The Nikon 5000 scanner (Nikon Corp., Tokyo, Japan) had average coefficients of variation of 0.4, 2.3, and 0.5 for the red, green, and blue channel levels across all runs. The P values of the correlation between the red, green, and blue color channel levels and the width of the large retinal arteriole were .89, .27, and .58, respectively. The results suggest that the tested scanners digitize the 35-mm slides in a reliable manner without biasing the retinal vessel measurements.
    Ophthalmic Surgery Lasers and Imaging 01/2010; 41(1):60-6. · 1.46 Impact Factor
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    ABSTRACT: To assess indices of nuclear sclerosis derived from digitized images made from color (slide) photographs. Film-based slit lamp images taken at baseline and at 5- and 10-year follow-up examinations of the Beaver Dam Eye Study cohort were digitized, and optical traces were taken along an axis through the center of the cornea and lens. Four indices of the severity of sclerosis were calculated based on the optical densities. The associations of the original Beaver Dam grades and these indices to age, vision, and change in severity of sclerosis over two subsequent visits were compared. At baseline photographs, the Spearman correlation between age and severity was 0.65 for the original film-based grading (n = 4518 right eyes) and varied between 0.46 and 0.71 for the measures from digitized images. Correlations of the indices to visual acuity were 0.38 for the film-based grading and ranged from 0.32 to 0.38 for the other indices. The authors assume that nuclear sclerosis does not regress and the percentage of regression is a reflection of error in grading. The percentage of regression and progression of sclerosis over 5- and 10-year intervals was determined for each index. After 5 years, 48.2% progressed and 4.9% regressed, using the Beaver Dam grades; progression occurred in 4.9% to 9.9%, and regression occurred in 4.5% to 7.0% for the other indices. After 10 years, 61.9% progressed and 3.2% regressed using the Beaver Dam grades; progression occurred in 8.0% to 19.7%, and regression occurred in 2.6% to 9.7% for the other indices. Semiautomated grading of the digitized images can be used to process thousands of images with little oversight by a trained grader. Indices of sclerosis that closely parallel human grading in their relationships to age and visual acuity can be easily computed. However, the indices appear to identify significantly less progression of nuclear sclerosis than does human grading. Further development to define a useful metric for identifying severity and progression of nuclear sclerosis is needed.
    Investigative Ophthalmology &amp Visual Science 05/2005; 46(4):1155-62. · 3.44 Impact Factor
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    ABSTRACT: Neitz film-based retroillumination cameras, the standard for documenting retroilluminated lens opacities for epidemiologic studies, are no longer produced. A digital imaging system is now available for imaging these opacities. We sought to compare gradings of images from both systems. Comparison of technique. One hundred fourteen lenses were imaged with both systems and graded according to protocols. Concordance between the methods was compared using kappa statistics. There was moderate concordance for cortical opacities (kappa = 0.63) and good concordance for posterior subcapsular opacities (kappa = 0.83). Grades from digital images slightly underestimated the frequency and severity of cortical cataract. Digital imaging of retroilluminated lens opacities results in similar classification of the severity of opacities. It will be useful for epidemiologic studies of cortical (CC) and posterior subcapsular cataracts (PSC).
    American Journal of Ophthalmology 11/2004; 138(4):668-70. · 4.02 Impact Factor
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