Canthaxanthin retinopathy. An investigation by light and electron microscopy and physicochemical analysis.

The eyes of a patient with canthaxanthin retinopathy were obtained at autopsy and examined by light and electron microscopy. Various tissues of one eye were also studied by physicochemical methods. Morphologically, there were red, birefringent, lipid-soluble crystals in the inner layers of the entire retina. They were particularly large and numerous perifoveally, where they were also clinically visible, but they also occurred frequently in a ring-shaped form peripherally and, less frequently, equatorially. The crystals were located in a spongy degeneration of the inner neuropil, where atrophy of the inner parts of the Müller cells was noticed. The compound isolated from the retina was identical with synthetic canthaxanthin according to mass and proton-resonance spectroscopy. Quantitatively, the retina contained up to 42 micrograms canthaxanthin per gram of tissue besides a minor amount of other carotenoids. Of the other tissues of the eye, only the ciliary body contained measurable concentrations of canthaxanthin. From the great number and size of the crystals, on the one hand, and the relatively small amount of isolated canthaxanthin on the other, it was concluded that the crystals presumably represent a canthaxanthin-lipoprotein complex rather than pure canthaxanthin alone. Examination showed that clinically, only the central portion of the canthaxanthin thesaurismosis, where crystals are packed most densely, can be seen.