Relationships Among Visual Acuity Demands, Convergence, and Nystagmus in Patients With Manifest atent Nystagmus Libe Gradstein, MD,a Herschel P. Goldstein, PhD, a--& Sheryl S. Wizov, COA,a Takao Hayashi, MD, c and Robert D. Reinecke, MD a.b Background:We investigated the role convergence plays in nystagmus dampening, in particular, relationships among visual acuity demands, convergence, and nystagmus. Previously we showed that subjects with idiopathic infantile nystagmus exhibit a range of responses to acuity targets, one of which is nystagmus blockage syndrome. We report herein eye movement responses to acuity targets of patients with manifest/latent nystagmus. Methods: Fourteen patients, 11 with latent or manifest latent nystagmus and 3 with combined manifest latent with infantile nystagmus, were asked to indicate the direction of the gap in Landolt C optotypes while their eye movements were recorded. Results:The tested patients exhibited various responses to acuity demands: (1) dampening of nystagmus with con- vergence (i.e., nystagmus blockage syndrome) (5/14 patients), (2) changes in vergence without nystagmus dampening (2 patients), (3) decrease of nystagmus without convergence (2 patients), and (4) little change in nystagmus or ver- gence (5 patients). In nystagmus blockage syndrome the amount of convergence increased with acuity demands in two of five patients and the convergence duration in four of five patients; nystagmus dampening increased with acu- ity demands in one of five patients and the blockage duration in four of five patients. Conclusions: Many, but not all, patients with manifest/latent nystagrnus, similar to those with infantile nystagmus, used convergence to dampen their nystagmus. The convergence response tended to increase with acuity demands, but the amount of dampening was idiosyncratic and not predictably related to the measured convergence across patients. (J AAPOS 1998;2:218-29) L atent nystagmus is a jerk nystagmus that develops at an early age and occurs with monocular view- ing. The fast phase beats to the side of the view- ing eye and the slow phase is a decreasing velocity expo- nential.i, 2 Manifest latent nystagmus is similar to latent nystagmus but present when both eyes are open and only one eye is used for vision. Studies, however, have shown that most subjects who are believed to have latent nys- tagmus on clinical examination have small amplitude manifest latent nystagmus evident by eye movement recordings with both eyes open) It is logical therefore to From the Foerderer Eye Movement Center for Children, Wills Eye Hospital, a the Department of Ophthalmology, Jefferson Medical College of Thomas ffefferson University,b Philadelphia, Pennsylvania, and the Department of Ophthalmology, Teikyo University School of Medicine, Tokyo,Japan. c Supported by a postdoctoral fellowship from the Fightfor Sight research division of Prevent Blindness America (L. G.). Presented at the AnnuaI Meeting of the American Associationfor Pediatric Ophthalmology and Strabismus, Charleston, South Carolina, April 2-6, 1997. Submitted April 5, 199Z Revision acceptedJanuary 7, 1998. Reprint requests: Libe Gradstein, MD, Foerderer Eye Movement Center for ChiMren, Wills Eye Hospital, 900 Walnut St., Philadelphia, PA 1910Z Copyright © 1998 by the American Assodationfor Pediatric Ophthalmology and Strabismus. 1091-8531/98 $5.00 + 0 75/1/89674 combine these two types of nystagmus into one group, manifest/latent nystagrnus. Manifest/latent nystagmus is common in childhood, and its frequent association with strabismus, in particular congenital esotropia, 4, 5 aggravates visual impairment in these children. Amblyopia is common with manifest/ latent nystagmus, whereas binocular vision with normal stereopsis is rare. 4 The cause of manifest/latent nystag- mus is unknown, with both sensory and motor mecha- nisms being proposed to account for it. 3, 4, 6 Lack of binocularity during visual system maturation is one of the proposed factors in its pathogenesis. 7-10 Treatment of manifest/latent nystagmus is problematic, and the only available modalities today target improving the binocular- ity and not the nystagmus. 11-13 Several factors cause a reduction of visual acuity in manifest/latent nystagmus and other types of nystagmus.14 One of them is the degrading effect of image motion. In normal subjects retinal-image slip above 2.5 deg/sec degrades Landolt C resolution, is In congenital nystagrnus (which we prefer to call idiopathic infantile nystagmus, as was proposed by Borchert et al., 16 because it is usually not apparent at birth I7) visual acuity correlates with the time eyes spend moving at a velocity equal to or less than 10 218 August 1998 7ournal of AAPOS