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G. Taibbi, Z. I. Wang, L. F. Dell'Osso; Infantile Nystagmus Syndrome: Broadening the High-Foveation-Quality Field With Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2008;49(13):140. doi: https://doi.org/.
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To investigate whether contact lenses are able to broaden and improve the high-foveation-quality field in a subject with Infantile Nystagmus Syndrome (INS).
A high-speed, digital video system was used for eye-movement recording. The subject was asked to fixate a target at different horizontal gaze angles with contact lenses inserted. Data from a previous study for the same subject, who performed the same trials viewing at far without refractive correction and at near at a convergence angle of 60 PD, were retrieved for comparison. The eXpanded Nystagmus Acuity Function (NAFX) was used to evaluate the foveation quality at each gaze angle.
Contact lenses broadened the high-foveation-quality range of gaze angles in this subject. The broadening was comparable to that achieved during 60 PD of convergence although the NAFX values were lower (shown in Figure).
Contact lenses employ afferent feedback (exteroception) via the ophthalmic division of the V cranial nerve to damp INS slow phases over a broadened range of gaze angles. Convergence and tenotomy have the same effects; proprioceptive feedback has been hypothesized for the tenotomy procedure. Contact lenses allowed the subject to see "more" (he had a wider range of high-foveation-quality gaze angles) and "better" (he had improved foveation at each gaze angle). This supports the proprioceptive hypothesis of INS improvement.
Figure. Fixation data (Eye Position vs. Time) for the subject during far viewing with contact lenses at different gaze positions: -20° (a), 0° (b) and 25° (c). In (d), plots of NAFX vs. Gaze Angle for far viewing, far viewing with contact lenses, and while converged (60 PD). Fitted polynomial curves are shown. Positive gaze angles indicate rightward gaze and "Conv" is convergence.
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