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Electroretinography in congenital idiopathic nystagmus
Electroretinography in Congenital Idiopathic Nystagmus G e r h a r d W. Cibis, M D * a n d K a t h l e e n M. F i t z g e r a l d , AS+
Ganzfeld electroretinograms were recorded from 105 consecutive patients clinically believed to have congenital idiopathic nystagmus. Retinal disease causing congenital nystagmus was diagnosed in 59 patients (56%). Electroretinographic evaluation of children with nystagmus and apparently normal eyes has both diagnostic and prognostic value. In patients with congenital nystagmus with a normal ocular examination, a diagnosis of congenital idiopathic nystagmus cannot be inferred without electroretinographic evidence of normal retinal function. Cibis GW, Fitzgerald KM. Electroretinography in congenital idiopathic nystagmus. Pediatr Neurol 1993;9: 369-71.
Introduction A recent mini-review of nystagmus in infancy recommended classification of nystagmus with an onset before 6 months as early-onset nystagmus [1]. The authors made the distinction between congenital idiopathic nystagmus (CIN), sensory defect nystagrnus (SDN), and neurologic nystagmus. SDN results from poor vision related to anterior visual pathway disease, while neurologic nystagmus is a primary nystagmus associated with neurologic disease, implying a normal eye and visual pathway. CIN is not associated with any evident visual or neurologic impairment, is often sex-linked, and has a relatively good visual acuity prognosis. The authors reported the importance of classification of early-onset nystagmus for proper diagnosis and patient management [1]. Differentiation of SDN from CIN by pendular versus jerk waveforms is not feasible [1,3]. Both are "different manifestations of the same ocular motor instability" [3]; therefore, CIN, which has a good visual prognosis, is a diagnosis of exclusion. SDN is claimed to represent 82-91% of early-onset nystagmus [1]. Many causes of SDN can be readily identified by clinical examination, therefore eliminating the need for electroretinography (ERG) and imaging studies. The use of ERG and cranial imaging studies in the evalu-
From the *Department of Ophthalmology; tVision Sciences Laboratory; Children's Mercy Hospital; Kansas City, Missouri.
ation of early-onset nystagmus is questioned [1-4]. Yee did not include ERG in his recommendations for evaluating nystagmus in small children [4], while Brodie suggested electrophysiology as an initial test [2]. Recent publications concerning the value of ERG in congenital nystagmus agreed that a high percentage of patients with no clinical evidence of visual pathway disease had abnormal ERGs [5,6]; however, patients with SDN, identifiable by clinical examination, were included in the patient population. What proportion of patients with CIH on the basis of clinical, neurologic, and visual pathway evidence actually has retinal abnormality? Weiss and Biersdorf examined 81 patients with "normal appearing eyes" and reported a 91% incidence of SDN following clinical examination and electrophysiology [5]. Included were 34 patients (42%) of ocular or oculocutaneous albinism diagnosed clinically by hypopigmentation of the skin and hair, iris transillumination, and/or macular hypoplasia. Similarly, of the 152 patients with congenital nystagmus studied by Gelbart and Hoyt [6], 13 (9%) were classified as having CIN because of the inclusion of 41 patients (27%) with optic nerve hypoplasia, while 39% of Table 1. Incidence of retinal origin sensory defect nystagmus diagnosed by electroretinography* Sensory Defect Nystagmus (n = 59; 56% t) Rod-cone dystrophy (n = 19; 18%) Rod monochromat (n = 16; 15%) Cone dystrophy (n = 10; 9%) Cone-rod dystrophy (n = 9; 9%) Unclassified retinal dystrophy (n = 4; 4%) Congenital Leber amaurosis (n = 1; 1%) * After ruling out neurologic or visual pathway disease in 105 patients with nystagmus who had no clinical evidence of sensory or neurologic defect. -t Congenital idiopathic nystagmus was observed in 46 patients (44%).
Communications should be addressed to: Dr. Cibis; 4620 J.C. Nichols Parkway; Suite 421; Kansas City, MO 64112. Received February 25, 1993; accepted July 7, 1993.
Cibis and Fitzgerald: Idiopathic Nystagmus 369
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Figure 1. Representative ERGs from each classification. (A) Normal response from a 2-year-old child: a- and b,waves noted with arrow. Response to blue flash is dominated by rod system, rapid oscillations to red flash represent contribution from the cone system. Response to a bright White flash yields a mixed rod and cone response. Oscillatory potentials are rapid wavelets observed on the ascending b-wave to a bright white flash~ When the slow activity is filtered out, using a 30-1,550 Hz bandpass, the faster frequencies are better observed. Responses to transient and steady-state (30 Hz) stimuli on a 10 Ft-L background after light adaptation are cone responses. (B) Normal response from CIN patient. (C) ERG from a r¢~l monochromat. Note absence of all cone responses. (D) Rod-cone dystrophy. Rod and cone responses are attenuated; rod responses have a greater effect. (E) Cone dystrophy. Rod responses are preserved and cone responses are attenuated. (F) Leber congenital amaurosis. At age 3 months the ERG is highly attenuated to absent. At age 1 year, no response couM be recorded. (G) Cone-rod dystrophy. Rod and cone responses are attenuated; cone responses have a greater effect. (H) Unclassified retinal dystrophy. Rod and cone responses are attenuated and implicit times delayed.
their p a t i e n t s h a d a b n o r m a l cranial c o m p u t e d t o m o g r a p h y (CT), s u g g e s t i n g a n e u r o l o g i c origin. Our study u s e d E R G to s e p a r a t e S D N o f retinal origin f r o m C I N w h e n the c a u s e o f n y s t a g r n u s w a s not clinically evident. T h e s e data are n o t available in t h e literature [3] a n d are n e e d e d to d e t e r m i n e t h o s e p a t i e n t s w i t h n y s t a g m u s w h e n E R G is m a n d a t o r y . I m a g i n g studies m a y not b e n e e d e d w h e n E R G e s t a b l i s h e s the d i a g n o s i s .
Methods The patients included 105 consecutive infants and children observed by the authors in their private office or at Children's Mercy Hospital.
370 PEDIATRIC NEUROLOGY
Vol. 9 No. 5
These patients were referred to the electrophysiology laboratory because of apparent CIN with no clinically evident neurologic or sensory defect. All were between 6 months and 15 years of age with a history of nystagmus onset observed prior to 6 months of age. Patients with SDN were excluded from this study whenever the cause of poor vision could be clinically identified. Albinism. albinoidism, and clinically apparent structural ocular defects, such as cataract, leukoma. optic nerve hypoplasia, macular hypoplasia, aniridia, and optic nerve colobomas as the cause of nystagmus, were excluded from our study. We also excluded clinically blind children and. therefore, most patients with Leber congenital amaurosis. Those children with neurologlc or systemic defects or with suspected spasmus nutans were also excluded. The pupils of the eyes tested were dilated with 1.0% tropicamide and 2.5% phenylephrine hydrochloride drops. The patients' eyes were dark-
adapted for 45 min. Children younger than age 3 years and those who were uncooperative were sedated with 50-75 mg/kg of oral chloral hydrate syrup following parental consent. The cornea was anesthetized with 0.5% proparacaine hydrochloride and a contact lens electrode was inserted under dim long-wavelength illumination. The eyes were tested simultaneously. Following dark adaptation, stimulus flashes of short-wavelength (blue; Wratten filters 47, 47A and 47B in combination, Eastman Kodak Co., Rochester, NY), long-wavelength (red; Kodak Wratten 26), and white (xenon) were presented in a ganzfeld bowl (Nicolet) under scotopic conditions. Flash luminance was attenuated using internal strobe settings and neutral-density filters (Wratten). In the photopic conditions a roddesensitizing background field of 10 F1 was used to isolate the cone response. The stimulus flash was white (xenon). Flash and backgrotmd luminances were calibrated with a photometer (model 350, United Detector Technology, Hawthorne, CA). ERGs were recorded with a monopolar "jet" contact lens electrode (Universo SA, Switzerland), referenced to the patient's ipsilateral mastoid with a forehead ground. Recordings were performed with a signal averaging system (CA-1000, Nicolet, Madison, WI). Conventional ERGs were recorded with a bandpass frequency setting of 1-1,500 Hz (-3 dB points). Oscillatory potentials were recorded with bandpass frequency settings of 30-1,500 Hz (-3 dB points). Responses were stored on floppy disks for later analysis. ERGs were recorded for a series of stimuli, first to the dark-adapted eye at 15 s intervals. One blue flash (-1.00 log cd-s/m2), 1 red flash (.66 log cd-s/m2), 2 separate white flashes, the first being the conventional ERG (1.72 log cd-s/m2) and the second the oscillatory potential (1.72 log cd-s/m2) were recorded at the filter settings described earlier. The eyes then were light-adapted to a rod desensitizing background of 20 FI for 10 rain. The light-adapted stimuli were presented with a 10 F1 background and consisted of 1 white flash (1.72 log cd-s/m2) followed by a 30 Hz flickering white light (0.79 log cd-s/m2).
Results The results are listed in Table 1. Of 105 patients suspected to have CIN, 46 (44%) had normal ERGs and were properly classified as having CIN. Fifty-nine (56%) were classified as having SDN by ERG abnormality, including 19 patients (18%) with rod-cone dystrophy, 16 patients (15%) with complete achromatopsia (rod monochromatism), 10 patients (9%) with cone dystrophy, 9 patients (9%) with cone-rod dystrophy, and 4 patients (4%) with unclassified retinal dystrophy (ERG abnormalities not classified by current terminology). One patient with Leber congenital amaurosis was found. Most patients with Leber congenital amaurosis exhibit severe vision loss and pendular nystagmus of the blind which would have excluded them from this study, but this patient had exhibited sufficiently good visual function with rapid nystagmus and was believed to have CIN. Our findings of an increased incidence of complete achromatopsia support those of Good et al. [7]. Representative ERGs for each classification are demonstrated in Figures 1A-1H.
Discussion We found that 56% of children with structurally normal eyes and visual systems with congenital nystagmus had underlying retinal diseases diagnosed by ERG. The remainder of the population (44%) could be properly classified as having CIN. Yee suggested clinical evaluation and imaging studies (i.e., CT or MRI) when evaluating nystagmus in children but failed to mention ERG [4]. We agree that once clinically obvious causes of SDN or neurologic nystagmus have been eliminated, imaging studies are appropriate, but emphasize that ERG is also indicated. In those patients in whom neurologic defects are not suspected, ERG would appear to be the test of choice. When ERG documents the diagnosis, imaging studies may not be needed. Conversely, once retinal disease is eliminated, the practitioner can decide whether imaging studies would be of value. It would be of interest to ascertain what percentage of the population at this point would demonstrate neurologic defects on imaging studies. Because it was not the purpose of this study, we do not know how many patients in our population may have developed neurologic nystagmus subsequently; we believe that it would be very small. Most patients with neurologic nystagmus have other clinical findings arousing suspicion leading to the diagnosis by neurologic examination or imaging studies. We conclude that ERG would be the primary choice of tests in the evaluation of children with nystagmus not associated with any clinically evident visual or neurologic impairment. We recommend subsequent imaging studies only when indicated which would aid in the proper classification of early-onset nystagmus and would be of both diagnostic and prognostic value to the patient with the most economical expenditure of diagnostic resources. References
[1] Casteels I, Harris KM, Shawkat F, Taylor D. Nystagmus in infancy. Br J Ophthalmol 1992;76:434-7. [2] Brodie SE. Choice of initial tests for nystagmus in infants. Arch Ophthalmol 1991; 109:464. [3] Dell'Osso LF, Flynn JT, Daroff RB. Hereditary congenital nystagmus. Arch Ophthalmol 1974;92:366-74. [4] Yee RD. Evaluating nystagmus in young children. Arch Ophthaltool 1990;108:793. [5] Weiss AH, Biersdorf WR. Visual sensory disorders in congenital nystagmus. Ophthalmology 1989;96:517-23. [6] Gelbart SS, Hoyt CS. Congenital nystagmus: A clinical perspective in infancy. Graefes Arch Clin Exp Ophthalmol 1988;226:178-80. [7] Good PA, Searle AET, Campbell S, Crews SJ. Value of the ERG in congenital nystagmus. Br J Ophthalmol 1989;73:512-5.
Cibis and Fitzgerald: Idiopathic Nystagmus 371
Ganzfeld electroretinograms were recorded from 105 consecutive patients clinically believed to have congenital idiopathic nystagmus. Retinal disease causing congenital nystagmus was diagnosed in 59 patients (56%). Electroretinographic evaluation of children with nystagmus and apparently normal eyes has both diagnostic and prognostic value. In patients with congenital nystagmus with a normal ocular examination, a diagnosis of congenital idiopathic nystagmus cannot be inferred without electroretinographic evidence of normal retinal function. Cibis GW, Fitzgerald KM. Electroretinography in congenital idiopathic nystagmus. Pediatr Neurol 1993;9: 369-71.
Introduction A recent mini-review of nystagmus in infancy recommended classification of nystagmus with an onset before 6 months as early-onset nystagmus [1]. The authors made the distinction between congenital idiopathic nystagmus (CIN), sensory defect nystagrnus (SDN), and neurologic nystagmus. SDN results from poor vision related to anterior visual pathway disease, while neurologic nystagmus is a primary nystagmus associated with neurologic disease, implying a normal eye and visual pathway. CIN is not associated with any evident visual or neurologic impairment, is often sex-linked, and has a relatively good visual acuity prognosis. The authors reported the importance of classification of early-onset nystagmus for proper diagnosis and patient management [1]. Differentiation of SDN from CIN by pendular versus jerk waveforms is not feasible [1,3]. Both are "different manifestations of the same ocular motor instability" [3]; therefore, CIN, which has a good visual prognosis, is a diagnosis of exclusion. SDN is claimed to represent 82-91% of early-onset nystagmus [1]. Many causes of SDN can be readily identified by clinical examination, therefore eliminating the need for electroretinography (ERG) and imaging studies. The use of ERG and cranial imaging studies in the evalu-
From the *Department of Ophthalmology; tVision Sciences Laboratory; Children's Mercy Hospital; Kansas City, Missouri.
ation of early-onset nystagmus is questioned [1-4]. Yee did not include ERG in his recommendations for evaluating nystagmus in small children [4], while Brodie suggested electrophysiology as an initial test [2]. Recent publications concerning the value of ERG in congenital nystagmus agreed that a high percentage of patients with no clinical evidence of visual pathway disease had abnormal ERGs [5,6]; however, patients with SDN, identifiable by clinical examination, were included in the patient population. What proportion of patients with CIH on the basis of clinical, neurologic, and visual pathway evidence actually has retinal abnormality? Weiss and Biersdorf examined 81 patients with "normal appearing eyes" and reported a 91% incidence of SDN following clinical examination and electrophysiology [5]. Included were 34 patients (42%) of ocular or oculocutaneous albinism diagnosed clinically by hypopigmentation of the skin and hair, iris transillumination, and/or macular hypoplasia. Similarly, of the 152 patients with congenital nystagmus studied by Gelbart and Hoyt [6], 13 (9%) were classified as having CIN because of the inclusion of 41 patients (27%) with optic nerve hypoplasia, while 39% of Table 1. Incidence of retinal origin sensory defect nystagmus diagnosed by electroretinography* Sensory Defect Nystagmus (n = 59; 56% t) Rod-cone dystrophy (n = 19; 18%) Rod monochromat (n = 16; 15%) Cone dystrophy (n = 10; 9%) Cone-rod dystrophy (n = 9; 9%) Unclassified retinal dystrophy (n = 4; 4%) Congenital Leber amaurosis (n = 1; 1%) * After ruling out neurologic or visual pathway disease in 105 patients with nystagmus who had no clinical evidence of sensory or neurologic defect. -t Congenital idiopathic nystagmus was observed in 46 patients (44%).
Communications should be addressed to: Dr. Cibis; 4620 J.C. Nichols Parkway; Suite 421; Kansas City, MO 64112. Received February 25, 1993; accepted July 7, 1993.
Cibis and Fitzgerald: Idiopathic Nystagmus 369
'b' & Normal, age 2
Stimulus l~rmnctcn: Scotorlc (no background)
~
b. Coegcmml nymlgmus, age 7 ye.a~
c. Rod monochromat, age 2 months
blue -LO0 leg Cd-~ec,/m2
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Figure 1. Representative ERGs from each classification. (A) Normal response from a 2-year-old child: a- and b,waves noted with arrow. Response to blue flash is dominated by rod system, rapid oscillations to red flash represent contribution from the cone system. Response to a bright White flash yields a mixed rod and cone response. Oscillatory potentials are rapid wavelets observed on the ascending b-wave to a bright white flash~ When the slow activity is filtered out, using a 30-1,550 Hz bandpass, the faster frequencies are better observed. Responses to transient and steady-state (30 Hz) stimuli on a 10 Ft-L background after light adaptation are cone responses. (B) Normal response from CIN patient. (C) ERG from a r¢~l monochromat. Note absence of all cone responses. (D) Rod-cone dystrophy. Rod and cone responses are attenuated; rod responses have a greater effect. (E) Cone dystrophy. Rod responses are preserved and cone responses are attenuated. (F) Leber congenital amaurosis. At age 3 months the ERG is highly attenuated to absent. At age 1 year, no response couM be recorded. (G) Cone-rod dystrophy. Rod and cone responses are attenuated; cone responses have a greater effect. (H) Unclassified retinal dystrophy. Rod and cone responses are attenuated and implicit times delayed.
their p a t i e n t s h a d a b n o r m a l cranial c o m p u t e d t o m o g r a p h y (CT), s u g g e s t i n g a n e u r o l o g i c origin. Our study u s e d E R G to s e p a r a t e S D N o f retinal origin f r o m C I N w h e n the c a u s e o f n y s t a g r n u s w a s not clinically evident. T h e s e data are n o t available in t h e literature [3] a n d are n e e d e d to d e t e r m i n e t h o s e p a t i e n t s w i t h n y s t a g m u s w h e n E R G is m a n d a t o r y . I m a g i n g studies m a y not b e n e e d e d w h e n E R G e s t a b l i s h e s the d i a g n o s i s .
Methods The patients included 105 consecutive infants and children observed by the authors in their private office or at Children's Mercy Hospital.
370 PEDIATRIC NEUROLOGY
Vol. 9 No. 5
These patients were referred to the electrophysiology laboratory because of apparent CIN with no clinically evident neurologic or sensory defect. All were between 6 months and 15 years of age with a history of nystagmus onset observed prior to 6 months of age. Patients with SDN were excluded from this study whenever the cause of poor vision could be clinically identified. Albinism. albinoidism, and clinically apparent structural ocular defects, such as cataract, leukoma. optic nerve hypoplasia, macular hypoplasia, aniridia, and optic nerve colobomas as the cause of nystagmus, were excluded from our study. We also excluded clinically blind children and. therefore, most patients with Leber congenital amaurosis. Those children with neurologlc or systemic defects or with suspected spasmus nutans were also excluded. The pupils of the eyes tested were dilated with 1.0% tropicamide and 2.5% phenylephrine hydrochloride drops. The patients' eyes were dark-
adapted for 45 min. Children younger than age 3 years and those who were uncooperative were sedated with 50-75 mg/kg of oral chloral hydrate syrup following parental consent. The cornea was anesthetized with 0.5% proparacaine hydrochloride and a contact lens electrode was inserted under dim long-wavelength illumination. The eyes were tested simultaneously. Following dark adaptation, stimulus flashes of short-wavelength (blue; Wratten filters 47, 47A and 47B in combination, Eastman Kodak Co., Rochester, NY), long-wavelength (red; Kodak Wratten 26), and white (xenon) were presented in a ganzfeld bowl (Nicolet) under scotopic conditions. Flash luminance was attenuated using internal strobe settings and neutral-density filters (Wratten). In the photopic conditions a roddesensitizing background field of 10 F1 was used to isolate the cone response. The stimulus flash was white (xenon). Flash and backgrotmd luminances were calibrated with a photometer (model 350, United Detector Technology, Hawthorne, CA). ERGs were recorded with a monopolar "jet" contact lens electrode (Universo SA, Switzerland), referenced to the patient's ipsilateral mastoid with a forehead ground. Recordings were performed with a signal averaging system (CA-1000, Nicolet, Madison, WI). Conventional ERGs were recorded with a bandpass frequency setting of 1-1,500 Hz (-3 dB points). Oscillatory potentials were recorded with bandpass frequency settings of 30-1,500 Hz (-3 dB points). Responses were stored on floppy disks for later analysis. ERGs were recorded for a series of stimuli, first to the dark-adapted eye at 15 s intervals. One blue flash (-1.00 log cd-s/m2), 1 red flash (.66 log cd-s/m2), 2 separate white flashes, the first being the conventional ERG (1.72 log cd-s/m2) and the second the oscillatory potential (1.72 log cd-s/m2) were recorded at the filter settings described earlier. The eyes then were light-adapted to a rod desensitizing background of 20 FI for 10 rain. The light-adapted stimuli were presented with a 10 F1 background and consisted of 1 white flash (1.72 log cd-s/m2) followed by a 30 Hz flickering white light (0.79 log cd-s/m2).
Results The results are listed in Table 1. Of 105 patients suspected to have CIN, 46 (44%) had normal ERGs and were properly classified as having CIN. Fifty-nine (56%) were classified as having SDN by ERG abnormality, including 19 patients (18%) with rod-cone dystrophy, 16 patients (15%) with complete achromatopsia (rod monochromatism), 10 patients (9%) with cone dystrophy, 9 patients (9%) with cone-rod dystrophy, and 4 patients (4%) with unclassified retinal dystrophy (ERG abnormalities not classified by current terminology). One patient with Leber congenital amaurosis was found. Most patients with Leber congenital amaurosis exhibit severe vision loss and pendular nystagmus of the blind which would have excluded them from this study, but this patient had exhibited sufficiently good visual function with rapid nystagmus and was believed to have CIN. Our findings of an increased incidence of complete achromatopsia support those of Good et al. [7]. Representative ERGs for each classification are demonstrated in Figures 1A-1H.
Discussion We found that 56% of children with structurally normal eyes and visual systems with congenital nystagmus had underlying retinal diseases diagnosed by ERG. The remainder of the population (44%) could be properly classified as having CIN. Yee suggested clinical evaluation and imaging studies (i.e., CT or MRI) when evaluating nystagmus in children but failed to mention ERG [4]. We agree that once clinically obvious causes of SDN or neurologic nystagmus have been eliminated, imaging studies are appropriate, but emphasize that ERG is also indicated. In those patients in whom neurologic defects are not suspected, ERG would appear to be the test of choice. When ERG documents the diagnosis, imaging studies may not be needed. Conversely, once retinal disease is eliminated, the practitioner can decide whether imaging studies would be of value. It would be of interest to ascertain what percentage of the population at this point would demonstrate neurologic defects on imaging studies. Because it was not the purpose of this study, we do not know how many patients in our population may have developed neurologic nystagmus subsequently; we believe that it would be very small. Most patients with neurologic nystagmus have other clinical findings arousing suspicion leading to the diagnosis by neurologic examination or imaging studies. We conclude that ERG would be the primary choice of tests in the evaluation of children with nystagmus not associated with any clinically evident visual or neurologic impairment. We recommend subsequent imaging studies only when indicated which would aid in the proper classification of early-onset nystagmus and would be of both diagnostic and prognostic value to the patient with the most economical expenditure of diagnostic resources. References
[1] Casteels I, Harris KM, Shawkat F, Taylor D. Nystagmus in infancy. Br J Ophthalmol 1992;76:434-7. [2] Brodie SE. Choice of initial tests for nystagmus in infants. Arch Ophthalmol 1991; 109:464. [3] Dell'Osso LF, Flynn JT, Daroff RB. Hereditary congenital nystagmus. Arch Ophthalmol 1974;92:366-74. [4] Yee RD. Evaluating nystagmus in young children. Arch Ophthaltool 1990;108:793. [5] Weiss AH, Biersdorf WR. Visual sensory disorders in congenital nystagmus. Ophthalmology 1989;96:517-23. [6] Gelbart SS, Hoyt CS. Congenital nystagmus: A clinical perspective in infancy. Graefes Arch Clin Exp Ophthalmol 1988;226:178-80. [7] Good PA, Searle AET, Campbell S, Crews SJ. Value of the ERG in congenital nystagmus. Br J Ophthalmol 1989;73:512-5.
Cibis and Fitzgerald: Idiopathic Nystagmus 371