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M.S. Niemeyer, A.M. Scholte, J.A. Dunbar; Visual Target Size Effects on Vertical Fusional Amplitudes . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4088.
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Purpose: To study the effects of varying visual targets on distance vertical fusional amplitudes. Methods: Normal adult volunteers were recruited for the study. Ten subjects met the inclusion criteria, which were best corrected visual acuity of 20/20 in each eye and normal fusional responses to Worth Four Dot. An investigator masked to the nature of the target asked the subjects to report their subjective experience of diplopia as either a clear image, a blurred image, or a double image when gradually increasing amounts of base down prism were presented to one eye under binocular viewing conditions. Different distance visual targets were presented in random order, consisting of a single 20/20, 20/40, and 20/200 optotype and a video image. Results: The average vertical fusional amplitudes for all target types was 2.6 prism diopters (PD). Vertical fusional amplitudes for the single 20/20 optotype were 2.3 PD, for 20/40, 2.4 PD, for 20/200, 2.9 PD, and for the video image, 2.8 PD. Conculsions: Subjects showed an average of 0.5 PD increase in their vertical fusional amplitudes when the 20/200 optotype and video image targets were viewed.
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