title: Morphological variations of the peripapillary circle of Zinn-Haller by flat section.
abstract: OBJECTIVE
  To evaluate the morphometric and morphological variations of the circle of Zinn-Haller (CZH) in the human eye.
  
  
  METHODS
  42 human enucleated eyes were used in this study. After transverse flat thick sections were cut through the optic nerve and adjacent sclera, tissue sections were stained with haematoxylin and eosin or examined immediately by wet preparation under a light microscope. The average vessel diameter of the arterial circle and the average distance between the optic nerve head (ONH) and the arterial circle were determined. Various branching patterns of the CZH were also evaluated.
  
  
  RESULTS
  The vessel diameter of the arterial circle was 123 (SD 75) microm (range 20-230 microm). The distance of the CZH from the ONH margin was 403 (352) microm (0-1050 microm). The CZH gave off branches to the optic nerve and to the peripapillary choroid (PPC) with various branching patterns especially at the entry point of paraoptic short posterior ciliary artery.
  
  
  CONCLUSIONS
  The CZH exists within a variable distance from the ONH and its average diameter is similar to that of the central retinal vessels though it shows marked variation even in the same circle. The CZH also shows variable configurations in branching patterns. These variations may act as contributing factors that are responsible for the individual susceptibility of the anterior optic nerve and the PPC to circulatory disturbances.
authors.affiliation: Department of Ophthalmology, School of Medicine, Hanyang University, Seoul, South Korea.
authors.forename: M K
authors.initials: MK
authors.lastname: Ko
authors.forename: D S
authors.initials: DS
authors.lastname: Kim
authors.forename: Y K
authors.initials: YK
authors.lastname: Ahn
mesh_terms: D000328:Adult; D019842:Ciliary Arteries / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000033:anatomy & histology / Q000098:blood supply; D012590:Sclera / Q000033:anatomy & histology / Q000098:blood supply*