LED Based Dual Wavelength Heterochromatic Flicker Method for Separate Evaluation of Lutein and Zeaxanthin in Retina

Abstract

The decrease of density and consequentially optical density of macular pigment serves as a diagnostic mean for a number of ophthalmological pathologies, particularly as a risk factor for age related macular degeneration. Macular pigment absorbs light in short wavelength blue spectral range. Thus the optical density of macular pigment can be detected by various optical – both objective and subjective psychophysical techniques. Latter techniques use eye and brain visual pathways as spectral sensitive optical detector and decision maker, and exploit perception facility to process information flow in a unique manner to create various perception illusions. The psychophysical methods of detection of optical density of macular pigment include heterochromatic flicker photometry and minimum illusory motion photometry. We develop and employ a heterochromatic flicker photometry method where LEDs are used as visual stimuli. LED emission maximum wavelengths in blue spectrum region are chosen in range 445-460 nm, that corresponds to spectrally resolved maxima of light absorption for two types of macula pigments – lutein and zeaxanthin or in spectral range 500-510 nm, where lutein and zeaxanthin absorption have decay, that for both type of pigments have a detectable shift. Statistical dispersion of the results allows to use the difference between results of psychophysical measurements obtained for different LEDs to estimate the concentration of lutein and zeaxanthin in human retina.