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J Gustafsson, P Unsbo; Eccentric Correction in Low Vision Subjects with Central Visual Field Loss . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2004.
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Purpose: To evaluate if the correction of off-axis optical aberrations has any influence on the visual function in partially sighted subjects with large central scotomas who use eccentric fixation. Only the most important off-axis aberrations, oblique astigmatism and defocus are considered in this study. Methods: The peripheral refraction in the preferred eccentric fixation angle was measured with photorefraction using the PowerRefractor instrument from Tübingen, Germany. The average values from these measurements were used to prescribe the eccentric correction. To objectively analyse the impact on visual performance a ring target in High-pass Resolution Perimetry was used. The ring target was set to evaluate the detection and resolution threshold in the eccentric fixation angle, with and without eccentric correction in spectacle lenses. Contrast sensitivity with the Pelli-Robson chart was also measured. Results: In five of the seven subjects with large central scotomas and, correspondingly, large eccentric fixation angles, an objective improvement of visual performance was found. The results showed an improved threshold value for visual acuity when the eccentric (oblique) astigmatism and eccentric spherical refractive errors were corrected. Five subjects also showed an improvement of the contrast sensitivity function. The results corresponded well with the subjective improvements that the subjects reported after evaluating the new correction in practical use. Conclusions: Improving the optical image quality in the preferred retinal location for well-adapted users of eccentric fixation leads to an improved resolving capacity. This increases the possibility for the individual subject to use their remaining visual function. It also shows that there are optical limitations in visual function in larger off-axis angels.
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