Digital Image Capture and Quantification of Subtle Lens Opacities in Mice

Abstract

Abstract: : Purpose: The analysis of lenses in living mouse models becomes increasingly important as the use of targeted modification of functional genes becomes more practical. Research on lens transparency in animals can be limited by several factors that complicate reproducible documentation, including small eye size, subtle modes of opacity, and minimal scattering intensity. Methods developed for use in humans can be expensive and difficult to use for routine and systematic ophthalmic examinations of small experimental animals. Objective evaluation of the lens, using densitometry traces of digital images, is also important for spatial and temporal quantification of opacities. In response to these limitations and needs, we report a rapid method for digital image capture and image analysis of lens opacities in rats and transgenic mice using low cost components. Methods: The eyes of living, unanesthetized mice or rats are dilated with a 1:1 mixture of 10% Phenylephrine Hydrochloride and 1% Tropicamide. Slit lamp examinations (using a Nikon FS-2 slit lamp) are recorded by a Canon Optura Pi video camera on digital video tapes. Still images are captured from the video clips using Adobe Premiere and processed with Adobe Photoshop. Using the NIH imaging program, Image J, densitometry traces are taken through the center of the slit lamp image of the eye, plotted as a function of light scattering intensity, and normalized to the intensity at the cornea so that multiple images can be quantitatively compared. Results: This method allows the recognition and quantification of subtle opacities, such as the Six-5 deficient model for cataract in myotonic dystrophy (Nature Genetics 25:105) and the CP49-null (IOVS 43:3722) mouse, which were difficult to characterize. The high sensitivity of the system permits assessment of minor changes in transparency that occur at the earliest stages of opacification. Changes in transparency in the entire lens or in a region of the lens can be compared as a function of age and other experimental conditions. Conclusions: Quantitative digital image capture simplifies the recording and analysis of lens opacities in living animals. For all applications using living, unanesthetized mice or rats, the system was found to be rapid, simple and cost effective.

Keywords: cataract • imaging/image analysis: non-clinical • transgenics/knock-outs