title: The effect of cataract surgery and IOL implantation on the magnification of a fundus photograph: a pilot study.
abstract: OBJECTIVE
  The goal was to determine the effect of cataract surgery-induced change in ametropia and anterior chamber depth on the magnification of a fundus photograph.
  
  
  METHODS
  Fundus photographs were taken from 11 subjects undergoing cataract surgery and intraocular lens (IOL) implantation before and after surgery with a telecentric Zeiss and Topcon fundus cameras. The distance between two distinct fundus landmarks, i.e. two crossings of retinal vessels, was measured before and after surgery, and the results were compared to axial length and surgery-induced change in ametropia and anterior chamber depth. In addition, the change in the conversion factor of Topcon fundus camera was calculated and its correlation to axial length, change in ametropia and anterior chamber depth was analysed. Further, the change in the mathematical location of P', i.e. the second principal point of the eye in the formula of Bennett et al. (1994), was calculated.
  
  
  RESULTS
  Cataract surgery and IOL implantation did not significantly influence the magnification of a fundus photograph taken with a telecentric Zeiss or Topcon fundus camera even when ametropia changed markedly. Axial length and anterior chamber depth did not correlate with change in the magnification of a fundus photograph. The average change in the mathematical location P' due to surgery was -39.4%, SD 0.33.
  
  
  CONCLUSIONS
  Fundus photographs taken with a telecentric Zeiss or Topcon fundus camera can be reliably used to follow the size of fundus landmarks even if ametropia and anterior chamber depth are changed after cataract surgery and IOL implantation.
authors.affiliation: Department of Ophthalmology, Turku University Hospital, Turku, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Knaapi
authors.affiliation: Department of Ophthalmology, Turku University Hospital, Turku, Finland.
authors.forename: Tuomo
authors.initials: T
authors.lastname: Lehtonen
authors.affiliation: Department of Ophthalmology, Turku University Hospital, Turku, Finland.
authors.forename: Eija
authors.initials: E
authors.lastname: Vesti
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002386:Cataract / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002387:Cataract Extraction / Q000009:adverse effects*; D005260:Female; D005654:Fundus Oculi; D006801:Humans; D019654:Lens Implantation, Intraocular / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods*; D010865:Pilot Projects; D011184:Postoperative Period; D057234:Preoperative Period; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*
keywords: IOL
  ; cataract surgery; fundus photograph; magnification