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S.A. Kabanarou, C. Bellmann, M.D. Crossland, L.E. Culham, G.S. Rubin; Non-Foveal Fixation and Binocular Viewing in AMD . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2764.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Eccentric viewing develops in age-related macular degeneration (AMD) when central scotomas occur in both eyes. AMD often affects the two eyes differently regarding the size and the location of the scotomas. This binocular incongruity may interfere with the development of eccentric fixation, normal eye movement co-ordination and binocular function. Therefore, the locus of eccentric fixation (preferred retinal locus or PRL) in one eye may not correspond with the PRL in the other eye, nor with the PRLs used if the subject views with both eyes. The standard techniques for determining the PRL include the fundus camera and scanning laser opthalmoscope (SLO), both of which are monocular. Video eye trackers can be used to evaluate binocular fixation, but these do not tell us directly about the retinal locus for fixation. The purpose of this study is to investigate the development of PRLs in patients with advanced bilateral AMD under monocular versus binocular viewing conditions by a combined use of an SLO and a video eye tracker. Methods: Five patients with advanced bilateral AMD (aged 70-82 years) were included in the study. Four of them were tested with the SLO to identify their PRLs monocularly and with video presentation to identify their PRLs under binocularly viewing conditions. A previously described blind spot mapping technique (Kabanarou et al., ARVO 2002) was used to determine the location of the PRLs. In the remaining patient, PRLs were determined by mapping the blind spots under monocular versus binocular conditions using the video system only. Results: Two of the patients used the same retinal locations to fixate under monocular and binocular conditions although visual acuities were different between the two eyes (ranged from 6/18 to 6/60) and central scotomas appeared incongruous. The remaining three patients demonstrated a shift in their PRLs in their dominant eyes when viewing binocularly. The first of them shifted his PRL horizontally and vertically by 4.1 and 3.3 deg respectively, and the second patient 2.8 deg and 3.25deg. The third patient demonstrated only a 2.9 deg shift in the horizontal plane. Conclusions: There is evidence that when patients use non corresponding PRLs in order to fixate under monocular conditions they demonstrate a shift in their PRL when viewing binocularly. Somewhat surprisingly, this shift can occur even for the dominant eye.
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