title: Towards a quantitative OCT image analysis.
abstract: BACKGROUND
  Optical coherence tomography (OCT) is an invaluable diagnostic tool for the detection and follow-up of retinal pathology in patients and experimental disease models. However, as morphological structures and layering in health as well as their alterations in disease are complex, segmentation procedures have not yet reached a satisfactory level of performance. Therefore, raw images and qualitative data are commonly used in clinical and scientific reports. Here, we assess the value of OCT reflectivity profiles as a basis for a quantitative characterization of the retinal status in a cross-species comparative study.
  
  
  METHODS
  Spectral-Domain Optical Coherence Tomography (OCT), confocal Scanning-Laser Ophthalmoscopy (SLO), and Fluorescein Angiography (FA) were performed in mice (Mus musculus), gerbils (Gerbillus perpadillus), and cynomolgus monkeys (Macaca fascicularis) using the Heidelberg Engineering Spectralis system, and additional SLOs and FAs were obtained with the HRA I (same manufacturer). Reflectivity profiles were extracted from 8-bit greyscale OCT images using the ImageJ software package (http://rsb.info.nih.gov/ij/).
  
  
  RESULTS
  Reflectivity profiles obtained from OCT scans of all three animal species correlated well with ex vivo histomorphometric data. Each of the retinal layers showed a typical pattern that varied in relative size and degree of reflectivity across species. In general, plexiform layers showed a higher level of reflectivity than nuclear layers. A comparison of reflectivity profiles from specialized retinal regions (e.g. visual streak in gerbils, fovea in non-human primates) with respective regions of human retina revealed multiple similarities. In a model of Retinitis Pigmentosa (RP), the value of reflectivity profiles for the follow-up of therapeutic interventions was demonstrated.
  
  
  CONCLUSIONS
  OCT reflectivity profiles provide a detailed, quantitative description of retinal layers and structures including specialized retinal regions. Our results highlight the potential of this approach in the long-term follow-up of therapeutic strategies.
authors.affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Marina
authors.initials: M
authors.lastname: Garcia Garrido
authors.affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Susanne C
authors.initials: SC
authors.lastname: Beck
authors.affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Regine
authors.initials: R
authors.lastname: Mühlfriedel
authors.affiliation: Section of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Julien
authors.affiliation: Section of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schraermeyer
authors.affiliation: Division of Ocular Neurodegeneration, Institute for Ophthalmic Research, Centre for Ophthalmology, Tuebingen, Germany.
authors.forename: Mathias W
authors.initials: MW
authors.lastname: Seeliger
mesh_terms: D000818:Animals; D005451:Fluorescein Angiography / Q000662:veterinary; D005849:Gerbillinae; D008252:Macaca fascicularis; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009887:Ophthalmoscopy / Q000662:veterinary; D011237:Predictive Value of Tests; D051381:Rats; D012160:Retina / Q000473:pathology*; D013045:Species Specificity; D041623:Tomography, Optical Coherence / Q000379:methods* / Q000662:veterinary*