Evaluation of OPTOS wide-field fundus image projections for radiotherapy planning of uveal melanoma

Abstract

Purpose

To investigate the relationship between the stereographic and azimuthal equidistant projection (AEP) of the human retina for radiotherapy planning with OPTOS optomap wide-field fundus images (Optos, UK). Further, the geometric accuracy of an OPTOS fundus image is quantified.

Methods

The fundamental relationship between both projection modes was applied to transform images acquired with an OPTOS Silverstone camera to the azimuthal equidistant projection using MATLAB. Fundus images of four patients were used to quantitatively demonstrate the impact for neglecting the proper projection. For that purpose, a delineated contour for each patient was analyzed if created in a treatment planning system, which assumes AEP, and compared with an OPTOS image. Furthermore, an eye model with a novel 3D printed retina pattern was used to quantify the geometric accuracy for an OPTOS optomap image.

Results

The difference between both projections was found substantial, leading to a change in delineated contours of more than 5 mm in the investigated cases and a change of delineated area of more than 40%. The geometric accuracy of OPTOS images of a customized eye model was found to be 0.2 mm on average, increasing to at most ∼0.5 mm at eye angles of 81°.

Conclusion

The fundamental difference in the representation of the eye fundus needs to be accounted for in radiotherapy planning of uveal melanoma. The basic underlying relationship for transformation is known, but more research is required to quantify other aberrations. The novel use of 3D printed retina patterns with known dimensions is providing a flexible approach for further investigations.