Apparent Retinal Vessel Width as a Function of Wavelength

Abstract

Abstract: : Purpose: To understand and quantify the effects of wavelength–dependent dispersion on the apparent size of retinal vessels and other structures as observed using imaging systems. Apparent changes in feature sizes as a function of wavelength may be a source of error for experimental techniques such as OCT which use broadband spectral beams for imaging. Methods: The structure of pressurized vessels within five enucleated swine eyes is imaged using a modified fundus camera with illumination provided by a scanning monochromator with 10 nm spectral resolution. Images are acquired every 10 nm from 440 to 700 nm. Sample arteries and veins are selected for cross–sectional analysis. Images are scaled and then aligned via cross–correlation, and the apparent width of the vessel as a function of wavelength is measured by an inflection point method. Differences in vessel width are also quantified directly using an image subtraction technique. Results: Differences in apparent vessel width as a function of wavelength on the order of 10% are observed over the experimental wavelength region, with the largest apparent widths observed at shorter wavelengths. Conclusions: Image processing methods are developed to quantify the apparent size of retinal features as a function of wavelength. Differences in feature size may be caused by dispersion within the eye, wavelength–dependent light scattering and absorption by the vessel and/or its sheath, and chromatic aberrations within the imaging system.

Keywords: imaging/image analysis: non–clinical • retinal neovascularization • optical properties