Toward Using Hybrid Image as a Visual Acuity Assessment Tool

The visual acuity test is a routine part of an eye examination or general physical examination, particularly if there is a change in vision or problems with vision. In most places, the Snellen chart is used to test visual acuity in humans. The Snellen chart usually comprises of many optotypes, which sizes decreasing along with subsequent rows. A person's visual acuity is determined by the smallest letter on the chart that he/she is able to identify. This visual acuity testing method requires a room with enough viewing distance. With the advent of new technology, computerized visual acuity assessment has been proposed and used in some clinical applications. This paper proposes an innovative media to assess human visual acuity using hybrid images. A hybrid image is an image that changes its meaning according to the viewing distance. It is an image composited from two different image's spatial frequency, high and low, accordingly. Based on the contrast sensitivity function, maximum sensitivity of spatial frequency is related to the viewing distance. With this assumption, we propose the use of hybrid image as a new tool to assess human visual acuity, starting with a pioneer vision experiment described in this paper. From the experiment, it was found that the hybrid images can discriminate between patients with vision problems and patients with normal vision, and that the difference detected is statistically significant.