In addition to real-world applications for normal vision, vertical text may have practical applications for some people with low vision, especially those who have a central scotoma. Age-related macular degeneration (AMD), which frequently causes scotomas in central vision, is the leading cause of visual impairment in developed countries. Afflicted patients must rely on their peripheral vision, making reading slow and difficult (Faye,
1984; Fine & Peli,
1995; Fletcher, Schuchard, & Watson,
1999; Legge, Ross, Isenberg, & LaMay,
1992; Legge, Rubin, Pelli, & Schleske,
1985). Evaluating the potential utility of vertically aligned letters in reading rehabilitation for people with AMD may yield beneficial results. Due to individual differences in retinal damage, the region of central-vision loss (scotoma) shows substantial variation across AMD patients. Patients often select a region in the peripheral visual field near the boundary of the scotoma for fixation and reading, called the preferred retinal locus (PRL). Previous studies have found that the majority of patients with central scotoma have either a left-field PRL or a lower-field PRL (Fletcher & Schuchard,
1997; Fletcher, Schuchard, Livingstone, Crane, & Hu,
1994; Sunness, Applegate, Haselwood, & Rubin,
1996; Timberlake et al.,
2005). If PRL locations were adopted purely by chance, only 25% of PRLs would fall into the left field, but the preference for a left-field PRL reached 63% in the study by Sunness et al. (
1996). For PRLs on the left or right of a scotoma, the scotoma will block a significant amount of the horizontal text and reading will be compromised. What kind of text format would be best for these AMD patients? Peli (
1986) suggested that the optimal direction of saccadic eye movements (reading direction) for AMD patients is the tangential direction (orthogonal to the line connecting the fovea with the PRL), while saccadic eye movements along the radial line are more difficult.