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Year : 2020  |  Volume : 33  |  Issue : 4  |  Page : 1178-1185

Evaluation of the diagnostic value of visual electrophysiological examination in childhood nystagmus

1 Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Ophthalmology, Faculty of Medicine, Minia University, Minia, Egypt

Date of Submission23-Mar-2020
Date of Decision04-May-2020
Date of Acceptance10-May-2020
Date of Web Publication24-Dec-2020

Correspondence Address:
Noha K Gaber
Shibin El Kom, Menoufia Governorate
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mmj.mmj_94_20

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To evaluate the use of electroretinography (ERG) and recording of visual-evoked potentials (VEP) as diagnostic tools in children with early-onset nystagmus to clarify the need to include them as a basic step in the evaluation of cases of early-onset nystagmus, especially with normal ocular examination.
Nystagmus in children can be caused by many causes, starting from idiopathic motor nystagmus compatible with relatively good vision, ending with ocular abnormalities that impair vision or other neurologic abnormalities that may be life threatening. Knowledge of the exact diagnosis is essential in the rehabilitation of a visually impaired child.
Patients and methods
In 32 children with early-onset nystagmus, ERG was recorded under light sedation, and VEP were simultaneously recorded to flash stimulus in all patients.
The study comprised 64 eyes of 32 patients, with their age ranging from 3 months to 7 years. Indications for referral included children with early-onset nystagmus. Children with obvious cause for nystagmus were excluded from the study. Overall, 37.5% of children had been diagnosed as having retinal dysfunction, including cone dystrophy (6.3%) and cone/rod dystrophy (31.2%). Neurological nystagmus was recognized in 34.3% of children. Ocular albinism was diagnosed in 6.3% of cases. One (3.1%) case was diagnosed as optic nerve hypoplasia. Six (18.8%) cases were diagnosed as idiopathic nystagmus.
This study clarified the need to investigate children with nystagmus by ERG and suggested that the ERG was useful where the diagnosis was uncertain, particularly at an early age with no obvious cause on ocular examination. VEP are complementary to ERG and can be tested simultaneously. Visual electrophysiological examination of children with early-onset nystagmus can establish or exclude retinal and postretinal pathway dysfunction, thus assisting in its classification and subsequent rehabilitation.

Keywords: early-onset nystagmus, electroretinogram, visual-evoked potentials

How to cite this article:
Gaber NK, Shehab AA, El Mazar HM, El Sobky HM, Ibrahim AM. Evaluation of the diagnostic value of visual electrophysiological examination in childhood nystagmus. Menoufia Med J 2020;33:1178-85

How to cite this URL:
Gaber NK, Shehab AA, El Mazar HM, El Sobky HM, Ibrahim AM. Evaluation of the diagnostic value of visual electrophysiological examination in childhood nystagmus. Menoufia Med J [serial online] 2020 [cited 2021 Apr 19];33:1178-85. Available from: http://www.mmj.eg.net/text.asp?2020/33/4/1178/304518

  Introduction Top

Nystagmus is defined as an involuntary rhythmic oscillation of the eyes, and it can be confirmed relatively easily through direct observation of eyes and/or eye movement recordings. Nystagmus leads to reduced visual acuity owing to the excessive motion of images on the retina, and also the movement of images away from the fovea[1].

Although the term 'congenital nystagmus' is often used synonymously, nystagmus is seldom diagnosed at birth. Nystagmus in children is considered as a diagnostic challenge, because it can be caused by many causes, starting from idiopathic nystagmus that is just a pure motor defect and compatible with relatively good vision, ending with ocular abnormalities that impair vision or other neurologic abnormalities that may be life threatening. Distinguishing between these causes can be challenging[2]. Many cases have an apparently normal ocular examination, which makes the diagnosis more difficult[3].

Visual electrophysiology provides an objective assessment of the retina, optic nerve, and cortical responses and is useful in determining the cause of visual impairment or in monitoring of visual or neurological condition[4]. Many inherited genetic retina or optic nerve conditions are present during childhood, either as poor vision, nystagmus, photosensitivity, or with night vision problems. In some cases, visual symptoms may precede clinically visible retina and optic nerve changes, and this makes the diagnosis difficult[5].

Knowledge of the exact ophthalmological diagnosis is essential in the rehabilitation of a visually impaired child. The diagnosis clarifies the etiology and, consequently, the genetics of the disorder. It provides an explanation for various visual problems of the child, and it implies the prognosis. The diagnosis may contribute to decisions about reading print or Braille, or which forms of education or career are feasible[6].

Visual electrophysiological screening of infants with congenital nystagmus can establish or exclude retinal and postretinal pathway dysfunction. Therefore, complementary electroretinogram (ERG) and visual-evoked potential (VEP), which is a noninvasive approach for infants, enables an objective means for identifying the basis of congenital nystagmus, thereby assisting in its classification[7].

Analysis of the type of nystagmus may give guidelines toward making the diagnosis. The searching type is indicative of Leber's congenital amaurosis, whereas the pendular type of nystagmus is associated with ocular albinism, achromatopsia, and congenital stationary night blindness (CSNB). Congenital idiopathic motor nystagmus (CIMN) can be identified by observing the point of reversal, together with any compensatory head posture, or the development of a jerky nystagmus on lateral gaze[8].

Nystagmus waveforms can be viewed in detail via eye movement recordings. However, nystagmus waveforms are extremely variable, and many patterns can coexist[9].

There are groups of retinal and/or optic nerve abnormalities that can partially be diagnosed by ophthalmological examination. However, there are many retinal and neurological diseases that cause nystagmus, and yet the eyes are apparently normal, which increases the need for electrophysiological examination[10].

Even in case of congenital opacities of the refractive media of the eye, electrophysiological examination can inform us about the functional state of the optic nerve. These examinations have prognostic significance, as they can assess the visual functions before cataract surgery and can predict the visual outcome postoperatively[11].

Much clinical ERG work is based on the standards and recommendations of the International Society for Clinical Electrophysiology of Vision (ISCEV). The ERG is the mass response of the retina to a short duration flash (full-field ERG). In adults, ERGs are recorded using corneal electrodes with stimuli delivered via a Ganzfeld bowl. This approach is suitable with older children, but there are two distinct schools of thought in relation to the young child or infant. Some adopt the approach that children are simply young adults, and use the same techniques; inevitably, this requires sedation in some patients[12]. Other authors believe that clinically satisfactory data in children can be obtained using less-invasive techniques involving the use of surface recording electrodes with the age of the child kept in consideration. The maturation of ERGs in early and late infancy has been extensively reviewed[13].

The main value of ERG is differentiating CIMN from sensory forms of nystagmus in a child with nystagmus and a normal fundus. Full-field ERGs can identify a retinal etiology and, when combined with VEP recordings, may localize dysfunction to the level of the retina or optic pathways. Equally, exclusion of afferent visual pathway dysfunction may be an important contribution to the management[14].

The aim of this study was to evaluate the use of ERG and VEP in children with early-onset nystagmus and to what extent they can establish the diagnosis to estimate the need to enroll them within the basic steps for assessment of cases with early-onset nystagmus.

  Patients and Methods Top

This is a descriptive case series study. The patients were selected from the electrophysiology unit in a private center (Al Watany Eye Hospital) between April 2018 and April 2019. A written informed consent was obtained from the parents of all participants. The study was approved by the Ethics Committee of Human Rights, Faculty of Medicine, Menoufia University, and carried out in accordance with the tenets of the World Medical Association's Declaration of Helsinki.

The inclusion criteria were nystagmus or any other roving eye movements in children ageing from 3 months to 7 years that appear at birth or shortly after birth. All the included cases were full term at the time of birth. Children with poor fixation with searching eye movements within the same age group were included also. The exclusion criteria included patients with obvious discernable cause for nystagmus on ocular examination such as corneal opacities, cataract, glaucoma, or retinal detachment. Detailed history was obtained from all patients, including the demographic data, consanguinity, maternal risk factors during pregnancy or labor, history of incubation, any other systemic diseases or medication, other visual complaints such as nyctalopia or photophobia, age of onset of nystagmus, and family history of similar condition. The patients underwent complete ophthalmological examination, including visual acuity testing, cycloplegic refraction, detailed anterior segment examination, measurement of the intraocular pressure, and detailed fundus examination. Visual acuity was assessed in preverbal children using the CSM system and in verbal children using Snellen visual acuity chart. Snellen visual acuity values were expressed as the decimal values for statistical analysis. Manifest and cycloplegic refractions were measured using streak retinoscope in children less than 4 years and 1 Chome-5-2 Azusawa, Itabashi City, Tokyo 174-0051, Japan Topcon KR-8000 Auto Kerato/Refractometer in children more than 4 years. Cyclopentolate 0.5% eye drops were used under 6 months and 1% subsequently. Anterior segment was examined using slit lamp in children more than 4 years and using the surgical microscope in children less than 4 years while they were under general anesthesia. Detailed fundus examination was done using the indirect ophthalmoscope with + 20 D lens. Any of the signs such as strabismus, high refractive error, head nodding, abnormal head posture, or any pigmentary fundus abnormalities were documented.

The procedure of electroretinography

The tests were done using the Roland Consult Electrophysiological diagnostic system, RETI-port/scan 21 (Brandenburg, Germany). The procedure was done under light sedation in uncooperative children, whereas the older and more cooperative children underwent the examinations while they were alert. The first step of the procedure was dark adaptation for 20 min (according to the ISCEV standards) while the pupils were dilating. The electrodes were placed under dim red light, and stimulation was commenced after full time of dark adaptation to record the scotopic ERG; this was followed by 10 min of light adaptation before recording the photophobic ERG. The active electrode was H-K loop electrode touching the bulbar conjunctiva (local aesthetic eye drop is instilled), the reference electrode was gold cup electrode placed at the skin of the outer canthus of the eye, and the ground (common) electrode placed on the forehead. The stimulus was delivered via Ganzfeld bowl which was used to illuminate the retina uniformly. The full-field ERG was recorded according to the ISCEV standard protocol (2015 update), which consists of six responses[1]: dark-adapted 0.01 ERG (rod ERG)[2], dark-adapted 3 ERG (combined rod-cone standard flash ERG)[3], dark-adapted 3 oscillatory potentials[4], dark-adapted 10 ERG (strong flash ERG)[5], light-adapted 3 ERG (standard flash 'cone' ERG), and[6] light-adapted 30 Hz flicker ERG[15].

The procedure of visual-evoked potentials recording

The tests were done also using the Roland Consult Electrophysiological diagnostic system, RETI-port/scan 21. The VEPs are electrical potentials recorded from the scalp derived from electrical currents generated in the visual cortex in response to visual stimulation. The VEP indicates the function of the entire visual pathway from the retina to area V1 of the visual cortex and primarily reflects the central retinal projection to the occipital poles. Recording electrodes are positioned on the scalp according to anatomical landmarks using a standardized 'International 10/20 system' measurement method. The electrodes used are the gold cup electrodes. The skin was prepared by cleaning, and a suitable paste was used to ensure good and stable electrical connection. The active electrode was placed along the midline on the occipital scalp over the visual cortex at Oz, and the reference electrode was placed along the midline at Fz. The ground (common) electrode was placed at the vertex. The flash VEP was elicited (according to the ISCEV standards 2016 update) by a brief flash stimulus that subtended 20° of the visual field and delivered by the Ganzfeld bowl (the same used for ERG recording) in dimly illuminated room[16].

For both ERG and VEP records, monocular testing was the rule, and every response was at least recorded twice to ensure that the results are reproducible and consistent.

Statistical analysis

Data were collected, tabulated, and statistically analyzed using an IBM personal computer with Statistical Package of Social Science (SPSS), version 22 (SPSS Inc., Chicago, Illinois, USA), where the following statistics were applied: descriptive statistics, in which the database was prepared using EXCEL software, Microsoft office 2013 version. Quantitative data were expressed in the form of mean, SD, and range, and qualitative data were expressed in the form of numbers and percentages. Analytical statistics were used to find out the possible association between studied factors and the targeted disease. The used tests of significance included the following: c2 to study the association between two qualitative variables, and Fisher exact test for 2 × 2 tables when expected cell count of more than 25% of cases was less than 5. P value of more than 0.05 was considered statistically nonsignificant, P value of less than 0.05 was considered statistically significant, and P value of less than 0.001 was considered statistically highly significant.

  Results Top

This study included 64 eyes of 32 patients, of whom 21 (65.6%) were males and 11 (34.4%) were females. Their age ranged from 3.5 to 84 months, with a mean age of 32.8 ± 28.5 months. The mean age of onset of nystagmus was 7.66 ± 10.0 months [Table 1].
Table 1: Demographic data of the studied group

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Scotopic ERG was normal in 22 (68.7%) patients and abnormal in 10 (31.3%) patients. Photopic ERG was normal in 20 (62.5%) patients and abnormal in 12 (37.5%) patients. Both scotopic and photopic ERG were normal in 20 (62.5%) patients, indicating normal retinal function [Table 2].
Table 2: Electroretinogram examination of the studied group (n=32)

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Flash VEP was normal in six (18.7%) patients and abnormal in 26 (81.3%) patients [Table 3].
Table 3: Flash visual-evoked potential examination among the studied group (n=32)

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Collectively, both ERG and VEP were normal in six (18.7%) patients, indicating normal retinal and postretinal pathway function, and those patients were diagnosed as having CIMN. ERG was normal whereas VEP was abnormal in 14 (43.8%) patients diagnosed as having postretinal visual pathway dysfunction. They were further classified into optic nerve hypoplasia (one case, 3.2%), ocular albinism (two cases, 6.4%), and neurological nystagmus (11 cases, 34.2%). Both ERG and VEP were abnormal in 12 (37.5%) patients, indicating retinal dysfunction (the abnormal VEP is due to postretinal visual pathway dysfunction which occurs as a sequela). Those 12 patients were further classified into two (6.4%) cases of cone dystrophy (abnormal photopic and normal scotopic ERG) [Figure 1] and [Figure 2] and 10 (31.1%) cases of cone/rod dystrophy (abnormal photopic and scotopic ERG) [Figure 3] and [Figure 4], where one case of them was cone/rod dystrophy as a part of Bardet–Biedl syndrome [Table 4] and [Table 5].
Figure 1: (a) Normal scotopic 10.0 ERG. (b) Normal oscillatory potentials. (c) Severely reduced photopic 3.0 flicker 30 Hz. ERG, electroretinogram.

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Figure 2: Abnormal flash VEPs 12 Hz. VEP, visual-evoked potential.

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Figure 3: (a) Abnormal scotopic 0.01 and 3.0 ERG. (b) Abnormal oscillatory potentials. (c) Abnormal photopic 3.0 and flicker 30 Hz response. ERG, electroretinogram.

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Figure 4: Abnormal flash VEPs. VEP, visual-evoked potential.

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Table 4: Integrated electroretinogram and visual-evoked potential findings in the studied group

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Table 5: Final diagnosis by electrophysiological examination among the studied group (n=32)

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With the simultaneous use of ERG and VEP, we could reach the diagnosis in all cases of the study. There was statistically highly significant relation between ERG results and fundus and final diagnosis of cases. There was a statistically highly significant relation between flash VEP results and fundus and final diagnosis of cases (P < 0.001) [Table 6].
Table 6: Relation between electroretinogram examination and flash visual-evoked potential, fundus examination, and final diagnosis of the studied group (n=32)

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  Discussion Top

ERG and VEP recording are effective tools in diagnosis and classification of early-onset nystagmus. Several studies have investigated nystagmus in children, and many of them have demonstrated the value of using ERG and VEP recording in diagnosis and classification[17]. Being an objective tool raises their importance in evaluation of children with early-onset nystagmus and children with unexplained visual impairment[6]. Nystagmus in children is an important manifestation of many ocular diseases; some of them are obvious on routine ocular examination such as congenital cataracts, ptosis, and corneal opacities, whereas others have apparently normal eyes on examination and may remain so for several years[18]. Of particular importance in this context are children with retinal disorders. Leber's congenital amaurosis, achromatopsia, cone dystrophies, and CSNB syndromes, which require detailed electrophysiological examination to provide a diagnosis in the early stages and thus offer the parents appropriate genetic advice[19]. In addition, the characteristic-evoked potential features of ocular albinism have been defined, and this difficult disorder too may be identified with a combination of clinical suspicion, clinical examination (of the child and mother), and visually evoked cortical responses[20]. In our study, we investigated 32 children with early-onset nystagmus with normal or apparently normal ocular examination, and with the simultaneous use of ERG and VEP recording, we reached the diagnosis in all of them.

Grace et al .[21] investigated retrospectively 34 children with early-onset nystagmus. Overall, 58 of these children also underwent analysis of the VEP, and 12 patients were diagnosed as achromatopsia (rod monochromatism), seven cases of Leber's congenital amaurosis, eight cases of ocular albinism, five cases of idiopathic motor nystagmus, one case of CSNB, and one case of juvenile retinoschisis.

Brecelja and Stirn-Kranjca[8] examined 28 children less than 1 year with early-onset nystagmus. ERG was recorded with skin electrodes, and VEP were simultaneously recorded. The first recording was performed before the age of 1 year. Follow-up was performed between the ages of 7 months and 6 years (mean age, 2.7 years). ERG was detected to flash stimulus and VEP to flash and/or pattern-reversal stimulus. Retinal dysfunction was detected in 10 (36%) cases (eight Leber's congenital amaurosis, one achromatopsia, and one cone/rod dystrophy), postretinal dysfunction in 14 (50%) cases (six optic nerve hypoplasia, seven neurological nystagmus, and one case ocular albinism), and normal retinal and postretinal function in four (14% of children) cases. All those children with normal retinal and postretinal function had been diagnosed as congenital idiopathic nystagmus. They found simultaneous skin ERG and VEP to be noninvasive and well tolerated by infants, with reliable reproducibility and recommended using them for screening of infants with congenital nystagmus[8].

Fazzi et al .[22] studied 40 children with LCA presented with nystagmus or roving eye movement before 6 months to clarify the ocular and extraocular aspects of the disease. They reported that the finding of a nonrecordable or extinguished ERG in both photopic and scotopic responses and altered or markedly reduced VEPs are essential for diagnosis of LCA.

Cone dysfunction syndromes are heterogeneous group of retinal disorders that comprise an important cause of visual impairment in children. They had been investigated by many authors. For example, Aboshiha et al.[23] investigated 20 children, and five of them had rod monochromatism, five had progressive cone dystrophy, and 10 had rod/cone dystrophy. All children had early-onset nystagmus, and ERG was conclusive in all of them. They reported that absent photopic response and 30-Hz flicker response stands out in all cases. Scotopic responses are less affected in cases of rod/cone dystrophy and normal in pure cone dysfunction.

CSNB is a rare group of genetic retinal disorders that affect the photoreceptors, RPE, or the bipolar cells and comprise important cause for nystagmus and visual impairment in children. Professor Miyake had investigated CSNB since 1986. Miyake et al .[24] investigated 64 children with CSNB and showed that all had essentially normal fundi. ERG showed a normal a wave with extremely reduced b wave (negative ERG) when recorded with a single bright white stimulus in the dark. They classified these patients into two groups: complete and incomplete types based on the evaluation of ERG.

With the complementary use of VEP recording, there is more to add to the diagnosis. Abnormal VEP is present in postretinal dysfunction such as ocular albinism, optic nerve hypoplasia, and optic atrophy. In our study, two patients were diagnosed as having ocular albinism in whom flash ERG was normal, but flash VEP showed crossed asymmetry. From the right eye, a positivity was recorded over the right scalp and a negativity over the left scalp. From the left eye, VEP distribution was the opposite, with a positivity being recorded over the left scalp and a negativity over the right. This is consistent with previous studies that studied nystagmus in children. For example, Brecelj et al .[25] studied 39 children with nystagmus, and 14 of them were diagnosed as having ocular albinism. Flash VEP recording of all of them shows the characteristic crossed asymmetry typical of albinism associated with excessive decussation of monocular fibers at the chiasm. They considered this as pathognomonic for albinism.

In our study, flash ERG was normal, whereas flash VEP showed abnormalities in children with nystagmus owing to either optic nerve hypoplasia or neurological disorders. McCulloch et al .[26] studied 85 children with bilateral optic nerve hypoplasia to correlate between the results of initial electrophysiological examination and the final visual outcome. All cases showed normal flash ERG with decreased amplitude and increased latencies of flash VEPs, with the flash VEP being unrecordable in severe cases of optic nerve hypoplasia.

Neurological nystagmus owing to cerebral visual impairment is an important cause for nystagmus and visual impairment in children. Patients with these disorders had often been previously diagnosed by pediatricians or child neurologist and the role of electrophysiological examination is mainly to document the diagnosis, exclude any coexistent retinal disease, and monitor the follow-up. Kuba et al .[27] investigated fifteen children with cerebral visual impairment owing to perinatal asphyxia. All of them showed normal flash ERG and abnormal flash VEP. They found that the final visual outcome for those children was related to the degree of abnormality of the initial VEP recording.

Six patients in our study had normal ERG and VEP, and we diagnosed them as idiopathic motor nystagmus. This was correlated with the clinical finding of relatively good visual acuity, normal ocular examination, the presence of null point, and abnormal head posture. This is consistent with previous studies that investigated infantile nystagmus. Bertsch et al .[28] examined 202 children with early-onset nystagmus, and 20 patients of them had normal ERG and VEP and were diagnosed as pure motor nystagmus. Their study raised the importance of electrophysiological examination of children with early-onset nystagmus to differentiate between the different causes especially cases with apparently normal ocular examination such as ocular albinism and idiopathic motor nystagmus.

  Conclusion Top

We conclude that electrophysiological examination is an essential step in the assessment of children with early-onset nystagmus especially when the eyes are apparently normal on routine examination and should be enrolled within their medical records. It is important to reach the accurate diagnosis associated with early-onset nystagmus as soon as possible, not only for proper family and genetic counseling and functional prognosis but also for early visual rehabilitation. Delays or errors in assessing the visual status of young infants with nystagmus can have quite serious implications for early learning. Visual electrophysiological examinations are noninvasive procedures that enable an objective means for identifying the basis of early-onset nystagmus, thereby assisting in its classification. We are of the opinion that guidelines and standards for pediatric testing are needed to establish the normative data for pediatric examination protocols.

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Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]


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