Quantification of the image obtained with a wide-field scanning ophthalmoscope.

PURPOSE To quantify the angle of view, the magnification, and the quality of images acquired with an Optos 200Tx. METHODS We obtained fundus images of a model eye with the Optos 200Tx and recorded the maximal scale imaged in each direction. We measured the length of the scale bar and the interval of the scale bars at each angle and calculated the magnification. We also measured the contrast between scale bars and the intervals between scale bars. RESULTS The fundus image obtained with the Optos 200Tx covered 96, 101, 76, and 102° in the up, right, down, and left directions, respectively. Quantitative measurement showed that the overall image is stretched 1.12-fold in the horizontal direction with respect to the vertical. The magnification with respect to the posterior pole increased quadratically in all directions, most steeply in the vertical direction, reaching 2.0 × 1.5 in the most extreme case. The image quality was best in the left part and was worse in the inferior and superior parts. CONCLUSIONS The Optos 200Tx can obtain an image duplicated, with an angular range of approximately 200° horizontally and 170° vertically, with greatest limitation in the inferior direction. It should be noted that the most peripheral part of the image is significantly and unequally magnified. In addition, the contrast is not the same at all positions. The present data would serve as a guide to correct the peripheral magnification in future studies.