Low Vision Due to Cerebral Visual Impairment
Low Vision Due to Cerebral Visual Impairment
All individuals with CVI included in this study were seen in Bartiméus, an institute for diagnostics, rehabilitation and schooling of the visually impaired in the Netherlands, in the period 2002–2012. Assuming that the incidence of visual impairment in 3.1 million Dutch children aged 0–15 years is similar to the 8/100 000 per year reported in Scandinavia, approximately half of the annually recorded children with low vision in the Netherlands are seen at Bartiméus. All children were referred to Bartiméus by medical specialists, i.e. paediatricians, rehabilitation physicians, ophthalmologists, general physicians and orthoptists. The children were referred for different reasons, mostly because of suspected visual impairment. A minority was referred for further diagnosis such as electrophysiology. The majority of children lived at home with their parents and were seen in the outpatient facilities of the Institute. All investigations were performed by a pediatric ophthalmologist with assistance of a technical ophthalmological assistant and/or orthoptist. Visual acuity was measured mono- and binocularly with correction of the refraction error under controlled light conditions. Monocular vision was measured by covering one eye by a special device for occlusion which could be added to the glasses worn by the patient. Visual acuity in young children or in individuals with a young developmental age was measured by forced preferential looking (Teller Acuity Cards, 55 cm), or with "LH Symbols" (3 m). The confrontational method with white Stycar balls, 5 cm, was used to estimate the visual fields. The balls on a stick were presented in all quadrants by a person behind the individual investigated. A person in front looked for response to the presented object: eye movements, pointing or a verbal response. Eye alignment, fixation, following, and visual behavior were observed. A handheld slit lamp was used to assess the anterior segment. In mydriasis, funduscopy and retinoscopy were performed, whenever the patient and parents agreed. But in case of lack of cooperation funduscopy and retinoscopy were not always possible. Electroretinography was rarely performed, because of developmental age or behavioral problems. CVI was diagnosed when there was no other ocular diagnosis which could explain the visual impairment or visual field defect, and/or typical features such as poor fixation or crowding, and/or CVI were found at neuropsychological investigation. Neuropsychological investigation of the visual functions was, however, not possible in a majority of the individuals, because of their developmental age. Although, there are tests available from 2 years onwards, the tests used in Bartiméus in the past 10 years were only applicable in patients with a developmental age above six years. Crowding was measured with the C-test at 5 m or with a LH Symbols version of the C-test on 40 cm as described in Huurneman et al. and was defined increased when the crowded ratio was ≥2. Additional inclusion criteria were a first visit over a 10 years period between 1-1-2002 and 1-1-2012 and low vision, defined as a visual acuity of ≤0.3 or <1.6 cycles/cm at 55 cm or a visual field radius of ≤30° degrees. Under the age of three the visual acuity was measured by Teller Acuity Cards and defined as decreased, when the acuity in cycles/degree was below the normal range for their age reported by Courage and Adams. Exclusion criterion was a second ocular diagnosis causing low vision, such as cataract or retinopathy of prematurity. Optic nerve atrophy was not an exclusion criteria, because it can occur as a result of retrograde transsynaptic degeneration in CVI. Primary (hereditary) optic atrophy or congenital idiopathic nystagmus were excluded based on the history and results during ocular examination by the ophthalmologist. Bilateral amblyopia was excluded as refraction was measured and corrected if necessary.
The most recent ophthalmologic examination was used for further analyses, including binocular visual acuity, visual fields, strabismus, nystagmus, refraction error and the aspect of the optic disc. The use of vigabatrin was registered because of the risk of constriction of visual field. To identify potential causes of CVI we evaluated the genetic investigations, risk factors during pregnancy, birth, and neonatal/childhood period, and reports on cerebral imaging.
For the comparison of the ophthalmological findings the data of the individuals with acquired causes and with a genetic diagnosis were used. To avoid confounding factors, which may contribute to CVI, additional criteria were used to select the subgroups for this comparison. Individuals with West syndrome and hydrocephalus as well as individuals with a genetic diagnosis in combination with a gestational age <37 weeks, unknown gestational age or acquired causes (e.g. perinatal problems) were excluded. For the statistical analysis the Mann–Whitney U test and the Fisher's Exact test were used. A p-value below 0.05 was considered to be significant. To control for the false discovery rate at 0.05 we used the Benjamini-Hochberg method. This study was approved by the Ethics Committee of the Radboud university medical center (Commissie Mensgebonden Onderzoek, regio Arnhem-Nijmegen). According to the Committee informed consent was not necessary, because all data were processed anonymously. Local approval of the institute was obtained. The study was conducted according to the tenets of the Declaration of Helsinki.
Methods
All individuals with CVI included in this study were seen in Bartiméus, an institute for diagnostics, rehabilitation and schooling of the visually impaired in the Netherlands, in the period 2002–2012. Assuming that the incidence of visual impairment in 3.1 million Dutch children aged 0–15 years is similar to the 8/100 000 per year reported in Scandinavia, approximately half of the annually recorded children with low vision in the Netherlands are seen at Bartiméus. All children were referred to Bartiméus by medical specialists, i.e. paediatricians, rehabilitation physicians, ophthalmologists, general physicians and orthoptists. The children were referred for different reasons, mostly because of suspected visual impairment. A minority was referred for further diagnosis such as electrophysiology. The majority of children lived at home with their parents and were seen in the outpatient facilities of the Institute. All investigations were performed by a pediatric ophthalmologist with assistance of a technical ophthalmological assistant and/or orthoptist. Visual acuity was measured mono- and binocularly with correction of the refraction error under controlled light conditions. Monocular vision was measured by covering one eye by a special device for occlusion which could be added to the glasses worn by the patient. Visual acuity in young children or in individuals with a young developmental age was measured by forced preferential looking (Teller Acuity Cards, 55 cm), or with "LH Symbols" (3 m). The confrontational method with white Stycar balls, 5 cm, was used to estimate the visual fields. The balls on a stick were presented in all quadrants by a person behind the individual investigated. A person in front looked for response to the presented object: eye movements, pointing or a verbal response. Eye alignment, fixation, following, and visual behavior were observed. A handheld slit lamp was used to assess the anterior segment. In mydriasis, funduscopy and retinoscopy were performed, whenever the patient and parents agreed. But in case of lack of cooperation funduscopy and retinoscopy were not always possible. Electroretinography was rarely performed, because of developmental age or behavioral problems. CVI was diagnosed when there was no other ocular diagnosis which could explain the visual impairment or visual field defect, and/or typical features such as poor fixation or crowding, and/or CVI were found at neuropsychological investigation. Neuropsychological investigation of the visual functions was, however, not possible in a majority of the individuals, because of their developmental age. Although, there are tests available from 2 years onwards, the tests used in Bartiméus in the past 10 years were only applicable in patients with a developmental age above six years. Crowding was measured with the C-test at 5 m or with a LH Symbols version of the C-test on 40 cm as described in Huurneman et al. and was defined increased when the crowded ratio was ≥2. Additional inclusion criteria were a first visit over a 10 years period between 1-1-2002 and 1-1-2012 and low vision, defined as a visual acuity of ≤0.3 or <1.6 cycles/cm at 55 cm or a visual field radius of ≤30° degrees. Under the age of three the visual acuity was measured by Teller Acuity Cards and defined as decreased, when the acuity in cycles/degree was below the normal range for their age reported by Courage and Adams. Exclusion criterion was a second ocular diagnosis causing low vision, such as cataract or retinopathy of prematurity. Optic nerve atrophy was not an exclusion criteria, because it can occur as a result of retrograde transsynaptic degeneration in CVI. Primary (hereditary) optic atrophy or congenital idiopathic nystagmus were excluded based on the history and results during ocular examination by the ophthalmologist. Bilateral amblyopia was excluded as refraction was measured and corrected if necessary.
The most recent ophthalmologic examination was used for further analyses, including binocular visual acuity, visual fields, strabismus, nystagmus, refraction error and the aspect of the optic disc. The use of vigabatrin was registered because of the risk of constriction of visual field. To identify potential causes of CVI we evaluated the genetic investigations, risk factors during pregnancy, birth, and neonatal/childhood period, and reports on cerebral imaging.
For the comparison of the ophthalmological findings the data of the individuals with acquired causes and with a genetic diagnosis were used. To avoid confounding factors, which may contribute to CVI, additional criteria were used to select the subgroups for this comparison. Individuals with West syndrome and hydrocephalus as well as individuals with a genetic diagnosis in combination with a gestational age <37 weeks, unknown gestational age or acquired causes (e.g. perinatal problems) were excluded. For the statistical analysis the Mann–Whitney U test and the Fisher's Exact test were used. A p-value below 0.05 was considered to be significant. To control for the false discovery rate at 0.05 we used the Benjamini-Hochberg method. This study was approved by the Ethics Committee of the Radboud university medical center (Commissie Mensgebonden Onderzoek, regio Arnhem-Nijmegen). According to the Committee informed consent was not necessary, because all data were processed anonymously. Local approval of the institute was obtained. The study was conducted according to the tenets of the Declaration of Helsinki.
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