Congenital Nystagmus

Congenital Nystagmus; Infantile Nystagmus Syndrome; Horizontal Pendular Nystagmus; Optokinetic Nystagmus AbsentOscillations of the EyesThis 11 year old Italian boy was referred for evaluation of nystagmus. Emanuel is the second son in a family of two and his older brother, age 13, had no visual problem. Emanuel was born at term, normal delivery, birth weight 9 pounds. Neonatal and infant development was perfectly normal. A pediatrician in Rome first noted he had eye oscillations at birth but did not tell his mother at the time in case the boy failed to develop normally. As soon as he recognized that the child was showing normal neurological development he advised his mother of the presence of nystagmus. Emanuel was age 2 at that time. When he became school age, he needed glasses for reading and television. He sits at the first desk to see the blackboard and has difficulty seeing objects at distance. He plays soccer, baseball and volley ball and skis as well and also plays computer games on his computer. Neuro-ophthalmological examination: Very bright, intelligent boy Visual acuity uncorrected OD: 20/100, OS: 20/70 -1 With both eyes reads 20/60 -1 Visual fields, pupils normal Ocular motility examination: Normal head position, no head tilt or turn No head nodding or shaking Full eye movements OU Large amplitude nystagmus in primary and in lateral horizontal and vertical gaze. Null point is just left of the midline. Nystagmus is suppressed on convergence No latent nystagmus OKN nystagmus could not be superimposed. Suppressed horizontal vestibular ocular reflex on rotation Funduscopic examination: 1. Partial fundus hypopigmentation and 2. Macular dysplasia/hypoplasia The fundus findings may represent ocular albinism or a genetically determined photo receptor degeneration. The presence of nystagmus favors the former diagnosis. Although not conclusive, the changes seen in the macula suggest dysplasia or hypoplasia of the macula which is also more commonly seen in patients with ocular albinism. See Figures 1-4 photographs of the right and left fundus showing macular hypoplasia. Basic electronystagmogram showed: 1. Spontaneous ocular oscillations throughout the record except when the eyes were closed. • The nystagmus had an inverted cosine waveform with smooth peak directed leftward except on rightward gaze where the waveform was inverted (i.e. cosine waveform with smooth peak directed rightward). • The frequency of the oscillation was 4 ± 0.3 Hz. the right eye deflection had a phase lead of around 72° to the left eye. • The intensity of the oscillation was greatest in leftward gaze and least in rightward gaze. Eye closure abolished the oscillation. • Latent nystagmus was not tested. 2. Saccades - Normal. superimposed oscillations except in extreme rightward gaze eccentricities. 3. Pursuit (tracking) 0.2 Hertz: Sinusoidal 0.3 Hertz: Sinusoidal 4. Optokinetic nystagmus - No optokinetic nystagmus was observed. Impression: There findings were considered to be consistent with congenital nystagmus and suggest an abnormality in fixation pathways.This little boy with the infantile nystagmus syndrome and macular hypoplasia has: • Primary position large amplitude pendular nystagmus • No head turn or nodding • No latent nystagmus • Nystagmus is suppressed on convergence Classification: The Classification of Eye Movement Abnormalities and Strabismus Working Group has recommended new names for nystagmus that begins during infancy. Three categories have been defined: 1. Infantile Nystagmus Syndrome (INS), which corresponds to what had previously been called motor or sensory forms of congenital nystagmus. 2. Fusional Maldevelopment Nystagmus Syndrome (FMNS), which corresponds to latent nystagmus occurring in association with amblyopia and strabismus and 3. Spasmus Nutans Syndrome (SNS). Diagnostic features of each of these syndromes are summarized in (ref 8). Box 10-11 Clinical features of Infantile Nystagmus Syndrome (See Chp 10, p513) Box 10-12 Clinical features of Latent Nystagmus (FMNS) (See Ch 10 p517) Box 10-13 Clinical features of Spasmus Nutans Syndrome (See Chp 10 p519) The congenital ‘nystagmus' of INS maybe present at birth but usually develops during infancy. Although variable in wave form (the commonest are increasing-velocity and pendular), certain clinical features usually differentiate INS from other ocular oscillations. • INS is almost always conjugate and mainly horizontal, even on up or downgaze. • A torsional component to the nystagmus is probably common but may be difficult to identify clinically. • Less commonly the nystagmus of INS is mainly seesaw and such patients may have underlying disease of the retina, visual pathways or cerebellum. • Life long nystagmus that is vertical is not typical of INS, and consideration should be given to other diagnoses such as the calcium channelopathies. • Nystagmus of INS is usually accentuated by the attempt to fixate on an object, and by attention or anxiety. • Eyelid closure or convergence, usually suppress it, but occasionally the nystagmus is evoked by viewing a near target. • Often nystagmus decreases when the eyes are moved into a particular position in the orbit; this is called the null point or zone, and corresponds to the range of eye position within which slow-phase eye velocity is at a minimum. • In some patients, especially albinos, the nystagmus periodically reverses direction, but this reversal seldom occurs in the regular manner seen in the acquired form of PAN. Stereovision: is usually degraded, even in children lacking strabismus, partly due to retinal image motion. Oscillopsia: Children with congenital nystagmus rarely complain of movement of visual images (oscillopsia). Head turns: Head turns are common in INS and are used to bring the eye and the orbit close to the null point or zone, which nystagmus is minimal. The presence of such head turns in childhood photographs is often useful evidence in diagnosing INS. Nystagmus blockage syndrome: Another strategy used by patients with either INS or the latent nystagmus of FMNS is to purposely induce an esotropia (nystagmus blockage syndrome) in order to suppress the nystagmus; such an esotropia requires a head turn to direct the viewing eye at the object of interest. Head oscillations: Some patients with INS also show head oscillations. Such head movements are not compensatory and tend to increase when the individual attends to an object, an effort that also increases the nystagmus. It seems possible, therefore, that in most patients head tremor and ocular oscillations represent the output of a common neural mechanism. Associated visual system defects: Overall, most children with congenital forms of nystagmus have no associated visual system defects, but in this boy's case he was found to have macular hypoplasia and partial hypopigmentation of the retina. The fundoscopic appearance is shown in Figure 1, A, OD and B, OS. (See Table 10-7 Visual system disorders associated with INS Chp 10 p513. (ref 8)). Familial INS: INS either, with or without associated visual system abnormalities may be familial. Autosomal dominant, and sex-linked recessive forms of inheritance have been reported. In x-linked forms, the mother may show subtle ocular motor abnormalities. The hereditary forms of INS, with the characteristic wave forms should be differentiated from other genetic disorders that produce forms of nystagmus typical of cerebellar dysfunction.Macular hypoplasiaCongenitalSurgical procedures for congenital nystagmus are discussed in (ref 8.)1. Abadi RV, Dickinson CM. Waveform characteristics in congenital nystagmus. Documents Ophthalmologica 1986;64:153-167. http://www.ncbi.nlm.nih.gov/pubmed/3608756 2. Abel, L.A., Wang, Z.I. and Dell'Osso, L.F.: Wavelet Analysis in Infantile Nystagmus Syndrome: Limitations and Abilities. Invest. Ophthalmol. Vis. Sci. 2008. (In Press). http://www.ncbi.nlm.nih.gov/pubmed/18450585 3. Averbuch-Heller L, Dell'Osso LF, Leigh RJ, Jacobs JB, Stahl JS. The torsional component of ‘horizontal' congenital nystagmus. J Neuro-ophthalmol 2002;22:22-32. http://www.ncbi.nlm.nih.gov/pubmed/11937902 4. Classification of Eye Movement Abnormalities and Strabismus (CEMAS) Working Group. http://www.nei.nih.gove/news/statements/cemas 2003. 5. Cogan D. Neurology of the Ocular Muscles, 2nd Edition. Charles C. Thomas Publisher, Springfield, Ill. 1956. 6. Hertle RW, Maldanado VK, Maybodi M, Yang D. Clinical and ocular motor analysis of the infantile nystagmus syndrome in the first 6 months of life. Br J Ophthalmol 2002;86:670-675. http://www.ncbi.nlm.nih.gov/pubmed/12034691 7. Hertle RW, Maybodi M, Mellow SD, Yang D. Clinical and oculographic response to Tenuate Dospan (diethylpropionate) in a patient with congenital nystagmus. Am J Ophthalmol 2002;133:159-160. http://www.ncbi.nlm.nih.gov/pubmed/11755862 8. Leigh JR, Zee DS. Diagnosis of Nystagmus and Saccadic Instrusions. Chp 10; 475-558. In: The Neurology of Eye Movements, Fourth Edition. Oxford University Press, NY 2006. 9. Shibasaki H, Motomura S. Suppression of congenital nystagmus. J Neurol Neurosurg Psychiatry 1978;41:1078-1083. http://www.ncbi.nlm.nih.gov/pubmed/731252 10. Stevens DJ, Hertle RW. Relationships between visual acuity and anomalous head posture in patients with congenital nystagmus. J Pediatr Ophthalmol Strabismus 2003;40:259-264. http://www.ncbi.nlm.nih.gov/pubmed/14560831MTemspoptokineticnystagmu