The effect of cataract surgery and IOL implantation on the magnification of a fundus photograph: a pilot study.

Purpose: 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.

Conclusion: 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.