The Effect of Zoom Magnification and Large Display on Video Comprehension in Individuals With Central Vision Loss

PURPOSE: A larger display at the same viewing distance provides relative-size magnification for individuals with central vision loss (CVL). However, the resulting large visible area of the display is expected to result in more head rotation, which may cause discomfort. We created a zoom magnification technique that placed the center of interest (COI) in the center of the display to reduce the need for head rotation. METHODS: In a 2 × 2 within-subject study design, 23 participants with CVL viewed video clips from 1.5 m (4.9 feet) shown with or without zoom magnification, and with a large (208 cm/82” diagonal, 69°) or a typical (84 cm/33”, 31°) screen. Head position was tracked and a custom questionnaire was used to measure discomfort. RESULTS: Video comprehension was better with the large screen (P < 0.001) and slightly worse with zoom magnification (P = 0.03). Oddly, head movements did not vary with screen size (P = 0.63), yet were greater with zoom magnification (P = 0.001). This finding was unexpected, because the COI remains in the center with zoom magnification, but moves widely with a large screen and no magnification. CONCLUSIONS: This initial attempt to implement the zoom magnification method had flaws that may have decreased its effectiveness. In the future, we propose alternative implementations for zoom magnification, such as variable magnification. TRANSLATIONAL RELEVANCE: We present the first explicit demonstration that relative-size magnification improves the video comprehension of people with CVL when viewing video.