The UV‐Absorption Spectrum of Human Iridal Melanosomes: A New Perspective on the Relative Absorption of Eumelanin and Pheomelanin and its Consequences^†

Abstract

Photoemission electron microscopy is used to measure the absorption coefficients, εc, of intact iridal stroma melanosomes isolated from dark brown and blue-green human irides for the spectral range λ=244-310 nm. These iridal stroma melanosomes were chosen because different colored irides produce organelles of varying eumelanin:pheomelanin ratios with similar size and morphology. Similar absorption spectra are found for the two types of melanosomes. The experimental spectra measured within are compared with both the extinction coefficient spectra obtained on soluble synthetic model systems and the monomeric precursors to each pigment.

Quantitative pigment extraction analysis for human pluripotent stem cell derived retinal pigment epithelial cells

“…The UV-Vis-spectra recorded here from synthetic melanin and from hESC-RPE extracts illustrates the complexity and the polymeric nature of the melanin-extracts. This result is in accordance with the published literature (10,13,14). Melanosomes of the RPE are non-transparent and appear in two shapes: elliptical melanosomes (0.5 to 1.0 µm in width, 1.0 to 2.5 µm in diameter), spherical or oval melanosomes (smaller one 0.5 to 1.0 µm, larger ones 1.5 to 2.0 µm) (15,16).…”

Uveal schwannoma in a brown‐eyed dog

“…Due to the natural lack of pigment, blue eyes are more exposed to UV‐induced oxidative stress and this in turn allows for a higher likelihood of a mutation occurring in the p53 tumor suppressor gene and thus potential neoplastic transformation of normal cells . There is a variation in the density of melanin in brown eyes in people; thus, despite having melanin, UV damage can still occur . This could potentially have been a contributing factor for the neoplastic changes observed in this case, as the dog's normal iris coloration was a ‘medium’ brown.…”

Chemical and biochemical control of skin pigmentation with special emphasis on mixed melanogenesis

“…In humans, PM and EM are present in various parts of the eye, such as in the iris and choroid‐retinal pigment epithelium (Sturm & Frudakis, 2004) (Figure 4a), where they mainly play photoprotective and anti‐oxidant roles (Biesemeier et al., 2011; Peles & Simon, 2012; Rózanowska, 2011; Weiter et al., 1986). Iris pigmentation affects the incidence of several important ocular diseases, including uveal melanoma and age‐related macular degeneration (Duffy et al., 2004; Sun et al., 2013; Wakamatsu et al., 2008).…”