Revisiting the internal absorption coefficient of the retinal pigment epithelium melanosome

R. D. Glickman, S. L. Jacques, R. T. Hall, N. Kumar

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Retinal pigment epithelial (RPE) cells of the vertebrate eye contain melanin packaged in structures called melanosomes. Previously, we reported that the bovine melanosome has a laser photodisruption threshold of 153.6 mJ/cm2 at 25 °C and 532 nm (Glickman et al., Proc SPIE 2681:460-467, 1996), and an internal absorption coefficient of 2237 cm-1 (Jacques et al., Proc. SPIE 2681:468-477, 1996). Those values used an estimate of melanosome density inferred from studies of skin laser effects (Jacques et al., J. Invest. Dermatol. 88:88-93, 1987). We now revisit that calculation using a density value obtained from density centrifugation analysis of bovine and baboon RPE melanosomes. Stepped-density gradients (60% to 80%) of the nonionic medium, Nycodenz, were formed, and samples of melanosomes were spun on the gradients in a swinging-bucket rotor at 10,000 rpm for 60 m. Bovine melanosomes formed two populations, one at the interface between 70% and 75%, and the other between 75% and 80%, corresponding to densities of ∼1.38 and ∼1.41 gm/cm3, respectively. Baboon melanosomes migrated to within the same density region. Using a density value of 1.41 gm/cm3, and assuming a water content of 52% for hydrated melanosomes, the internal absorption coefficient was calculated as 2339 cm-1. Although this calculation uses an objective density measurement, the water content remains an estimate, and the actual value in situ may differ.

Original languageEnglish (US)
Pages (from-to)134-141
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2001


  • Density
  • Laser photodisruption
  • Melanin
  • Nycodenz
  • Optical properties
  • RPE

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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