Measuring How Quickly the Eye Focuses After Sustained Viewing of Close-up Images and Videos

In this experiment, subjects will view a cross pattern on the screen and be asked to focus their eyes on it. The cross pattern will look like it is moving towards and away from the eye in a back-and-forth motion. As the subjects focus their eyes on the shapes, we will measure the focus of their eyes using a device called a wavefront sensor. This device uses infrared light to measure the optical properties of the eye in real time. Our goal is to find out how well the eye focuses before and after viewing images on a screen up close (25cm). Since many people spend a lot of time looking at a computer screen while at work or at school, it is important to understand how this affects the eye's ability to focus.

Inclusion Criteria: * We will recruit participants for inclusion who are adults in the age range of 18-35 years, because these are the ages at which people's eyes are able to focus at near distances. Exclusion Criteria: * Participants will be screened for having normal or corrected-to-normal (glasses/contacts) vision. Participants with vision worse than 20/20 will be excluded. People with fragile or loose teeth will be excluded because participants need to bite a piece of dental clay to stabilize their heads so that measurements can be taken from their eyes (too much head and eye movement disrupts the measurement). People who are pregnant, with heart disease, or personal/familial history of epilepsy will be excluded because some studies recommend against them viewing computer displays while sitting down for an extended period of time.