title: Morphometry of axons in optic nerves of Siamese's twins.
abstract: OBJECTIVE
  To observe the development of optic nerve, we examined four optic nerves from Siameses Twins by absolute counts of axons.
  
  
  METHODS
  Mean axon diameter, mean axon density, totally axonal population and optic nerve area were noted for each optic nerve. The mean axon diameter and the mean axon density were compared between paraxial (inner sectors) and cortical(outer sectors) areas of the nerves.
  
  
  RESULTS
  More myelinated axons were seen in the inner sectors as compared to the outer sectors (average 11 axons/1000 microm2 in inner sectors and 34 axons/1000 microm2 in outer sectors (P = 0.036). The myelinated fibers were also smaller (63 microns) in the outer sectors as compared to the inner sectors (72 microns) (P = 0.001). The average cross sectors area for the four 40 week stage optical nerves of Siamese Twins was 3.32 x 103 as compared to 1 million axons for 32-week-old normals.
  
  
  CONCLUSIONS
  Our finding of fewer axonal number and small myelinated fibers in the Siamese Twins suggests hypoplasia. Myelination was more abnormal in the paraxial optic nerve than that in the peripheral sectors, suggesting anomalous development of optic nerve peripherally and delayed developnent centrally. Axonal density is higher in inner sectors than that in outer sectors, suggesting delayed development of the outer nerve sector.
authors.affiliation: Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060 China.
authors.forename: Xinzu
authors.initials: X
authors.lastname: Gui
authors.forename: Zhenping
authors.initials: Z
authors.lastname: Zhang
authors.forename: Qi
authors.initials: Q
authors.lastname: Lin
authors.forename: Jiongji
authors.initials: J
authors.lastname: Liang
authors.forename: Wenyu
authors.initials: W
authors.lastname: Lu
authors.forename: Xiulan
authors.initials: X
authors.lastname: Ye
authors.forename: A A
authors.initials: AA
authors.lastname: Sadun
mesh_terms: D000886:Anthropometry; D001369:Axons / Q000473:pathology*; D002452:Cell Count; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009412:Nerve Fibers / Q000473:pathology; D009413:Nerve Fibers, Myelinated / Q000473:pathology; D009898:Optic Disk / Q000166:cytology; D009900:Optic Nerve / Q000098:blood supply / Q000473:pathology*; D014428:Twins, Conjoined / Q000473:pathology*