Comparative study of two calibration methods on fundus camera

Two photogrammetric camera calibration methods based on two calibration objects, i.e., 3-D and planar calibration objects, were used with a nonmydriatic fundus camera and the results were presented. Experimental results show that lens distortion plays a major role in the system error contribution and it is therefore necessary to be taken into account. Although the planar calibration pattern method is slightly more complex, it is found to be more robust and less sensitive to noises. From this method the calibration results achieved an error of approximately 0.6 pixel from an effective picture area of 752 × 582 pixels. These results could help obtaining a more accurate estimate of 3-D retinal surface profile from this type of fundus camera.