title: Magnification-corrected photodynamic therapy.
abstract: BACKGROUND
  To present a method for performing photodynamic therapy (PDT) with a constant predictable light fluence based on actual laser spot magnification.
  
  
  METHODS
  A calibrated Gullstrand-type model eye with a scale of half circles in the centre of the artificial fundus was used for this study. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the actual laser spot magnification of four indirect condensing laser lenses were determined using a PDT laser unit.
  
  
  RESULTS
  Equations for determining the actual laser spot magnification were calculated for each laser lens. The total change in laser spot magnification from hyperopia (axial length 20 mm) to myopia (axial length 31 mm) was -20% to +24.8% for Mainster Standard lens (Ocular Instruments Inc, Bellevue, Washington, USA), -15.7% to +27.7% for Mainster Wide Field lens (Ocular Instruments Inc), -16.3% to +33.1% for Volk Transequator lens (Volk Optical Inc, Mentor, Ohio, USA), and -19.2% to +24.4% for Volk PDT Laser lens (Volk Optical Inc).
  
  
  CONCLUSIONS
  Axial length of the eye has a considerable effect on PDT laser spot magnification when an indirect laser lens is used. By calculating the actual laser spot magnification in conjunction with knowledge of the true greatest linear dimension of the neovascular lesion, the clinician may be able to deliver a constant predictable amount of light fluence to the fundus independent of the axial length of the PDT treating eye.
authors.affiliation: Department of Ophthalmology, Medical University of Graz, Auenbruggerplatz 4, A-8036, Graz, Austria. ansarishahrezaei@yahoo.co.uk
authors.forename: Siamak
authors.initials: S
authors.lastname: Ansari-Shahrezaei
authors.forename: Erdem
authors.initials: E
authors.lastname: Ergun
authors.forename: Robert
authors.initials: R
authors.lastname: Chong
authors.forename: Adnan
authors.initials: A
authors.lastname: Tufail
authors.forename: Andreas
authors.initials: A
authors.lastname: Wedrich
authors.forename: Michael
authors.initials: M
authors.lastname: Stur
mesh_terms: D020256:Choroidal Neovascularization / Q000188:drug therapy; D006801:Humans; D006956:Hyperopia / Q000150:complications; D007834:Lasers; D008954:Models, Biological; D009216:Myopia / Q000150:complications; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011166:Porphyrins / Q000627:therapeutic use; D000077362:Verteporfin
chemical_list: D017319:Photosensitizing Agents; D011166:Porphyrins; D000077362:Verteporfin