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S.R. Tari, V.C. Greenstein, G.R. Barile, R.T. Smith, I. Barbazetto, W. Seiple; Determining Location, Stability and Function of the Preferred Retinal Locus in Macular Disease . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5827.
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© ARVO (1962-2015); The Authors (2016-present)
The characteristics of visual function of patients with preferred retinal locations (PRLs) are not fully understood. Here we used a variety of methods to assess the effects of different functional tasks on the location and stability of fixation. In addition the relationship of the PRL to pathologic features of the fundus was assessed.
Four patients with established PRLs were tested. Following pupil dilation, standard fundus examination and fundus autofluorescence (AF) were performed. Fixation locus was then assessed monocularly with standard fundus photography. The subject was instructed to fixate the end of a target. A series of three photographs were taken. Fixation was then recorded with the MP 1 (Nidek Inc.) that has a background luminance of 1.27cd/m2. The subject was instructed to fixate the center of a red cross (3° in diameter) and fixation was tracked for 30 seconds. This task was followed by threshold perimetry with the MP 1 Thresholds to "white" stimuli, (Goldmann III, 200 ms) were presented in an array subtending a radius of 6 deg. The subject was instructed to maintain steady fixation of a cross. Again fixation was tracked throughout perimetry.
There was agreement between fixation location assessed with fundus photography and the MP 1 fixation task. The MP 1 provided information regarding stability of fixation. Compared to patients with foveal fixation, the four patients with PRL showed more variability for the fixation task. Stability was >97% within a 1°radius for patients with foveal fixation compared to 90 –79% for patients with a PRL. This variability increased for both groups during the perimetry task. For patients with foveal fixation, stability decreased by 4–5% and for the patients with PRL it decreased by 56–81%. The results of AF showed that the patients with PRLs used retinal areas with a normal fluorescent pattern.
The results of these tests using different tasks to identify and monitor fixation suggest that the clinician and rehabilitation specialist should be aware of the effect of different functional tasks on fixation stability.
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