title: Choroidal structure in normal eyes and after photodynamic therapy determined by binarization of optical coherence tomographic images.
abstract: OBJECTIVE
  To determine changes in choroidal structure by binarization of optical coherence tomographic (OCT) images.
  
  
  METHODS
  Choroidal images were recorded by enhanced depth imaging OCT. The subfoveal choroidal images were analyzed, and the luminal and interstitial areas were converted to binary images by the Niblack method. The interrater, intrarater, and intersession agreements of the binary images were determined for healthy eyes. In eyes with age-related macular degeneration (AMD), the binary images of the choroid before photodynamic therapy (PDT) were compared to those after PDT. The untreated fellow eyes were studied as controls.
  
  
  RESULTS
  In healthy eyes, the average ratio of the luminal to choroidal area was 65.4%. The interrater agreement rate was high, with intraclass correlation coefficient (ICC) 0.985 and 0.988 for the choroid and luminal areas, respectively. The intrarater ICC was 0.996 for the choroid and 0.997 for the luminal areas. The intersession ICC was 0.993 for the choroid and 0.984 for the luminal areas. In eyes with AMD, the subfoveal choroidal area, the luminal area, and the interstitial areas were thinner 6 months after PDT (all P < 0.01, Wilcoxon signed-rank sum test). The ratio of the luminal to choroidal area was significantly decreased to 62.8% (P < 0.01, Wilcoxon signed-rank sum test). The ratio for the fellow eyes was not significantly changed.
  
  
  CONCLUSIONS
  The Niblack binarization method can be used to analyze the luminal area of choroid in an OCT image with good repeatability and reproducibility. The change in the subfoveal choroidal area after PDT is due mainly to a decrease in the luminal areas.
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Shozo
authors.initials: S
authors.lastname: Sonoda
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Taiji
authors.initials: T
authors.lastname: Sakamoto
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Yamashita
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Shirasawa
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Eisuke
authors.initials: E
authors.lastname: Uchino
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Terasaki
authors.affiliation: Department of Ophthalmology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Tomita
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001808:Blood Vessels / Q000502:physiology; D002829:Choroid / Q000098:blood supply / Q000473:pathology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010778:Photochemotherapy; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence; D057135:Wet Macular Degeneration / Q000188:drug therapy* / Q000503:physiopathology
keywords: EDI-OCT; age-related macular degeneration; choroid; vessel