Correction of spatial distortion and registration in ophthalmic fluorescein angiography

The study of indocyanine green (ICG) angiography in retinal and choroidal diseases has provided one significant advantages on the quantification of retinal and choroidal vessels. In order to compensate for the uneven magnification resulting from the hemispherical surface of the retina, 26 mm diameter phantoms were constructed. Two calibrated markers (grid patches) were planted on the surface of both the macular and peripheral regions. Parameter optimization methods were applied on both regions and then a series of images were taken from those regions by an ophthalmic fundus camera. Preliminary results on different angles of view have shown that the central region of the retina (macula) has minimum spatial distortion which can be ignored. However, the peripheral regions demonstrated large spatial distortion which need to be compensated for in future quantification measurements. The authors also demonstrate a correction method for the spatial distortion at peripheral regions, which was by parabolic realignment. Registration results, by using affine transformation, are also discussed here both with and without spatial correction. >