GEODESIC LENGTH MORPHOMETRY: A simple method for quantifying severe degeneration laterally in rodent models of...

Quantification of degeneration extent in curvilinear microscopic specimens, such as the retina, is challenging due to inherent geometric complexity. In the rodent retinal photic injury model, degeneration arc lengths are a critical, yet difficult-to-quantify parameter for assessing severity. We developed a novel, precise platform, termed "Geodesic Length Morphometry," that quantifies the actual arc lengths of curvilinear structures using a precisely determined digital scale factor. In this methodology, defining a curved coordinate axis along the retinal contour enables precise numerical localization of any position and the measurement of dorsoventral arc lengths between any two points. This robust platform resulted in two analytical innovations. One is a new visualization method, termed "Geodesic Equidistant-Projection Plot," which converts arc length data measured from curved anatomical imagery into a cumulative line chart, allowing for the direct visual comparison of actual degeneration arc length and location. The second is the definition of the "Geodesic Index" (0 ≤ x ≤ 1), which normalizes the degeneration arc length against the entire retinal arc length to enable an objective, size-independent comparison of extent of degeneration. The Geodesic Length Morphometry platform offers a robust standard for the quantitative analysis of curvilinear tissue arc length and serves as a versatile tool applicable to diverse biological and morphometric fields.