Introduction: Autostereograms first appeared in the nineteenth century when scientists took two slightly offset pictures and viewed them through a stereoscope, causing each separate image to be isolated to one eye. This slight disparity produces stereopis, perceived depth perception as a result of the brains comparison and interpretation of the two images together . From there psychologist Bela Julesz developed a similar illusion but used images of random dots with a slightly off set shape ingrained within. In the stereoscope the shape then appears to float over the background. Psychologist Christopher Tyler then further improved this design by creating the basis for the current autostereograms. Vertical strips, each containing alternating pieces of each shifted image, are made into a pattern, by looking "through" the pattern the strips blur into one another, causing a fused right and left eye image, creating depth. Since one of the best ways to view the stereograms is to "look through" it a person's eyes will have wider range of focus, or decreased ocular convergence. With myopia the lens has an excess of curvature that focuses images in front of the retina, allowing myopics to be able to focus easier on extremely close objects. Myopics have to do less to focus correctly on the image, lessening focus pressure. With this ability also comes the predisposition for the eyes to have a wider than normal ocular convergence. This might allow them to see three dimensional stereograms quicker than people with normal vision. We plan to study the effects of myopia and hyperopia in stereoscopic viewing as well as forced myopia in people with perfect 20/20 vision with weak reading glasses for hyperopics If subjects are more myopic, then they will be better able to see the three-dimensional autostereograms.
Methods: To perform our experiment we first prepared two sets six different autostereograms of similar black and white background and size and mounted them to plain white pieces of paper. Three of the test images were more easily viewed and three were more difficult to view, all of which featured an image that popped out at the viewer. The test images were then shown to 19 subjects; of which were approximately equal numbers of myopics, hyperopics, and subjects with perfect 20/20 vision done in one room of constant size and lighting. The test images were first shown to the subjects in a fixed order with their vision aids on if necessary so as to produce perfect vision in all subjects. The time for the image to be seen was recorded for each subject; if the image could not be obtained within a minute then it was passed over. After this portion was completed the subjects removed their vision aids if necessary or the people with 20/20, so as to make them more myopic, used mild, hyperopic correcting, reading glasses, testing the effects of altered eye focus. The same six test images were shown again in a different fixed order and time was recorded for obtainment with the same criteria. Throughout testing this procedure of viewing the images as less to more myopic was rotated every other subject so as to provide some control over learned viewing. A questionnaire was then used to evaluate each subjectís performance. It gathered information on subjects' sex, eye problems, strength of problems if any, and the results of viewing the test images. Subjects were asked to describe what they saw, if an image was obtained, and how clearly they were able to focus on the image.
Results: The graph showed that for myopics and induced myopics in subjects with 20/20 vision on the majority that the time taken to see the stereograms decreased as they went from more to less myopic. However, the hyperopic subjects tested decreased in time to obtain the images as they went from a more myopic state to a reduced one. An overall average was also taken for all of the test images for all three test groups. For these averages only the myopic group showed the decrease in time going from increased to decreased myopia. Both the hyperopics and those with normal vision increased in time taken for obtainment with the myopic increase, however the 20/20 subjects only differed in a value of one second overall.
Figure 1: The graph displays the composite grouping of the average times for each of the three test groups. The increase in time for attainment as myopic effect decreased can be seen in the myopic subjects; and while the other two groups had a decrease in time going from increased to decreased myopia, the 20/20 value, differing in only one second, still suggests a strong correlation between myopia and faster visual obtainment.