When the subject looks through the hologram, they will see the images of various sunburst patterns located at different distances from their eye. The subject will be asked to identify the sunburst patterns that appear to have all the lines uniformly blurred and two other patterns where one of the lines appears darkest/ sharpest than the other lines. From the location of these patterns in the array and from the orientation of the darkest lines seen, the astigmatism of the subject can be calculated.

Image Credit: Kodikullam Avudainayagam