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R.J. McLean, F.A. Proudlock, N. Sarvananthan, S.J. Farooq, I. Gottlob; Reduction of congenital nystagmus during monocular veiwing. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2521.
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Purpose:Usually if one eye is covered the waveform of nystagmus does not change when it is of congenital idiopathic in nature and in latent nystagmus the amplitude increases. We describe a patient with reduction of congenital idiopathic nystagmus during monocular viewing. Methods:A 56–year–old male with nystagmus from early childhood underwent ophthalmological examination, electrophysiology and eye movement recordings with a high–resolution infrared eye tracker (Eyelink, Sensomotoric Instruments). Eye movements were recorded at distant and near, under binocular and monocular viewing conditions with and without 10 prism base out. Results:Corrected distance visual acuity was 20/60 with both eyes open, 20/30 in the right eye and 20/40 in the left eye. He had horizontal conjugate nystagmus and habitually closed the left eye for better vision. He had no oscillopsia or manifest squint and stereoacuity of 150 sec arc. The nystagmus was significantly reduced on closing either eye and at near. He had a slight head turn to the right with a null point to the left. Scotopic and photopic electroretinograms were normal as well as dark adaptometry. Eye movement recordings revealed predominantly right, but also left beating horizontal conjugate nystagmus. The nystagmus had increasing velocities of the slow phase with foveation periods. At distance the nystagmus amplitude was between 2 and 6 degrees and the frequency was 1 to 3 Hz. During monocular viewing eye movement recordings showed mainly small square–wave jerks, and also intermittent low amplitude nystagmus (1–2 degrees). There were periods of stable fixation for up to 4 seconds. The nystagmus also dampened on convergence and at distance with 10 prism base out. Conclusions:We describe an unusual patient with congenital idiopathic nystagmus, in which occlusion of either eye increased visual acuity and reduced the nystagmus significantly, to small square–wave–jerks. This underlines the relationship betwen saccadic oscillations and congenital idiopathic nystagmus, as described during development of congenital idiopathic nystagmus (Gottlob IOVS 1997;38,767–773) and in latent nystagmus (Abadi et al. IOVS 2000,41,3805–3817). Mechanisms causing the nystagmus to be reduced on monocular vision are unclear, but may be related to abnormal neuronal pathways similar as in latent nystagmus, for example the NOT.
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