Mapping of fundus photography to 3D imaging for ocular radiotherapy

Abstract

Aims/Purpose: Ocular Proton Therapy (OPT) is one of the main treatments for uveal melanoma. Full inclusion of fundus images in the treatment planning is currently hindered by the refraction of the eye's optical elements. In this study we developed and evaluated a method to correct for these effects, with the final aim of enabling an OPT‐planning which spares more of the healthy retina.Methods: A paraxial method to correct for the scaling fundus photographs of the central retina was developed using ray transform matrices. This method was subsequently extended to the full retina using ray tracing simulations in Zemax OpticStudio through the ZOSPy library [1]. These methods were evaluated in 33 eyes in which the corneal topography, lens location, thickness and curvature, and retinal shape were personalized. The resulting scaling of the fundus images was finally compared with the method currently used in OPT planning (EYEPLAN).Results: For the central retina the magnification relative to the average eye ranged from 0.79 to 1.50 and was approximately inversely proportional to the eye's spherical equivalent. For the peripheral retina, a nodal point‐based mapping provided no systematic errors and the least variation between subjects (up to 2.5 degrees at 70degrees eccentricity). This method proved a significant improvement compared to the currently used method which had a systematic error of approximately 21 degrees as it incorrectly modelled the refractive effect of the eye's optics.Conclusions: Using the nodal point as a reference point, fundus images can be accurately mapped to 3D imaging, enabling the inclusion of optical information in OPT planning.