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S.E. Hill, H. Han, F. Thorn; Visual Posture and Focus During Recreational and Study Reading . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5598.
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Purpose:Visual posture (the relationship between head, eyes, and reading material) may contribute to retinal image quality, convergence and accommodation demands, binocular comfort and overall comfort and pleasure during reading. Reading distance may also affect hyperopic defocus and myopia development in children. Thus, we have examined the reading posture and accommodative lags of young adults while they read in two different settings with different font sizes. Methods: Eight optometry students read in a recreational setting, "Harry Potter and the Sorcerer’s Stone" in font sizes (9, 10, and 12 point font) while sitting in an armchair and in a study setting, "Adler’s Physiology of the Eye" in the same three fonts sizes while using a desk. Subjects read each assignment for 3 minutes and were filmed from the side with an iSight digital camera. Distance from eyes to book, downward angle of the book relative to the eyes, head tilt angle, and vertical gaze angle were determined at 10 second intervals. Accommodation was measured repeatedly in each condition with a PlusOptix II during a second session in which reading was restricted to the previously determined visual postures. Results: Reading distance was significantly closer in the study setting (31.1 cm) than the recreational setting (38.8 cm)(P=0.006) while reading distance increased slightly with font size for both settings (P=0.046). Subjects held "Harry Potter" about 43.2° below the eyes. "Adler" was left on the desk so the downward angle was much greater (62.8°)(P=0.0009). Subjects tilted their heads much less for "Harry Potter" (17.1°) than for "Adler" (37.4°)(P<0.0001). As a result the vertical angle of eye gaze was virtually identical for the two settings (26.3° vs 24.2°). Accommodative lag increased when text was held closer to the eyes. Conclusions: Visual posture was constrained by the setting and font size. Subjects reported that the most comfortable tasks involved larger font sizes held further from the eyes with a small head tilt in the recreational reading setting. These conditions may make reading more pleasurable for children and by reducing accommodative lag may reduce the likelihood of myopia.
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