title: Melanocytes and iris color. Electron microscopic findings.
abstract: OBJECTIVE
  To quantitatively associate iris color with melanocyte pigment content.
  
  
  METHODS
  Autopsy eyes were classified as uniform-blue, uniform-hazel, or uniform-brown or showing a darker peripupillary ring. Using electron microscopic images and computerized image analysis, area, number, and size of mature melanosomes within the perinuclear cytoplasmic area only or within perinuclear and peripheral cytoplasmic areas of the superficial stromal melanocytes combined were measured.
  
  
  RESULTS
  Average melanosomal area per perinuclear cytoplasmic area (AMAC) and average number of melanosomes per perinuclear area (AMNC) significantly differed across iris color groups (overall P<.001). This result reflects the large difference between blue-uniform and all other color groups. A marginally significant (nominal) trend from blue-ring through brown-ring was also detected (P=.06 for AMAC and P=.07 for AMNC). The average perinuclear cytoplasmic area was larger in the central iris zone (within 1 mm around the pupillary margin) than in the intermediate iris zone (between 1 and 2 mm around the pupillary margin) (P=.002), but AMAC and AMNC did not significantly differ between zones. The average melanosome size did not differ significantly across color groups (P=.11).
  
  
  CONCLUSIONS
  Differences in iris colors are at least partially attributed to variable AMNC and AMAC within superficial melanocytes.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, USA.
authors.forename: P D
authors.initials: PD
authors.lastname: Imesch
authors.forename: C D
authors.initials: CD
authors.lastname: Bindley
authors.forename: Z
authors.initials: Z
authors.lastname: Khademian
authors.forename: B
authors.initials: B
authors.lastname: Ladd
authors.forename: R
authors.initials: R
authors.lastname: Gangnon
authors.forename: D M
authors.initials: DM
authors.lastname: Albert
authors.forename: I H
authors.initials: IH
authors.lastname: Wallow
mesh_terms: D000368:Aged; D002452:Cell Count; D005127:Eye Color; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007498:Iris / Q000648:ultrastructure*; D008297:Male; D008544:Melanocytes / Q000648:ultrastructure*