title: Determination of absolute size of fundus objects.
abstract: BACKGROUND
  Creating multiple beam interference fringes on the retina using the "retina fringe projector" (RFP) provides us with a scale which can be used to determine the absolute size of objects at the fundus.
  
  
  METHODS
  The procedure is tested on an model eye, the optical parameters of which are varied in order to simulate different refraction conditions. The RFP was used to determine the size of a known object at the model fundus; the result was then checked against the real value of the object. In a second series of measurements, the RFP fringes were included in fundus photos of 52 patients with varying levels of ametropia, taken at the University Eye Clinic in Jena using the FF450 fundus camera (manufacturer: Carl Zeiss Meditec AG) for diagnostic purposes. The distance between the fringes was determined using both the RFP and the Littmann method.
  
  
  RESULTS
  The differences to the real value of the fundus size of a known object deviated on average by 1 to 2%, and always remained under 3% in the model eye. A very good correlation between RFP and Littmann methods results could be found in the clinical part of the study. The resulting deviations are below 2.5%.
  
  
  CONCLUSIONS
  Integration of a RFP in a fundus camera permits measurement of absolute values of the retina, regardless of the type of observation or documentation. Knowing the real size of fundus objects holds a potential in many clinical classification scales of fundus objects such as drusen or vessels, or in optimizing photodynamic therapy spot size measurement.
authors.affiliation: Department of Ophthalmology, University Hospital Jena, Bachstr. 18, 07749 Bachstraße 18, 07740, Jena, Germany. jens.dawczynski@med.uni-jena.de
authors.forename: Jens
authors.initials: J
authors.lastname: Dawczynski
authors.forename: Michael
authors.initials: M
authors.lastname: Gebhardt
authors.forename: Thomas
authors.initials: T
authors.lastname: Mohr
authors.forename: Ingo
authors.initials: I
authors.lastname: Koschmieder
authors.forename: Bernhard
authors.initials: B
authors.lastname: Rassow
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Schubert
authors.forename: Jürgen
authors.initials: J
authors.lastname: Strobel
mesh_terms: D001699:Biometry / Q000295:instrumentation; D005654:Fundus Oculi; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D010781:Photography / Q000295:instrumentation*; D012858:Size Perception
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