Evaluating visual function of mentally retarded children has long presented a challenge in the field of scientific research due to their limited subjective expression ability and poor examination cooperation, which results in low reliability of measured data. In this study, the objective far vision was evaluated using the German Roland electrophysiological scanning VEP (sweep VEP). The inspection principle of the equipment is that the signal generated by the retina in response to the stimulation of the black-and-white bar is transmitted through the visual pathway, and the electrical signal corresponding to the visual stimulation of the visual center of the cerebral cortex is recorded on the surface of the skull skin. The objective vision is obtained through computer processing, providing a certain reference for the diagnosis of damage to the visual pathway. This method does not require the subjective expression of the person being examined, making it ideal for evaluating the visual acuity of mentally retarded children. Regan[12]first used graphic VEP for visual acuity measurement as early as 1973. In PVEP waveforms with different spatial frequencies, a typical VEP response wave with the highest spatial frequency was recorded as the subject's VEP visual acuity. Later, it was replaced by 10-sized bars with different spatial frequencies. Studies have shown that black-and-white bar scanning visual evoked potential is more accurate and convenient than graphic reversal visual evoked potential. Our study showed that children with intellectual disabilities have an objective visual acuity that is significantly higher than their subjective visual acuity. The influence of cognitive ability and expression ability can result in a perceived visual acuity that is typically lower than the real visual acuity.
CP is often complicated by strabismus, and the proportion of ametropia is high. The rate of visual dysfunction is about 28.2% ~ 47% in 2007 and 2008[13][14]. Katoch et al[15]studied 149 patients with CP, including 78 patients with strabismus, representing a 52.3% incidence rate. The National Symposium on pediatric cerebral palsy classifies CP into five subtypes: spastic type, involuntary movement type, hypotonia type, mixed type, and ataxia type. Spastic type is the most common form of CP. ,Three different types of CP was spastic, dyskinesia, and ataxia types according to Gulati[16]. Patients who are diagnosed with hypotonic CP typically show signs of the condition from early infancy, which may develop a spastic type, dyskinesia type, or ataxia type CP with development. Reid[17]showed that the incidence of CP in children with intellectual impairment was between 40% and 65%. The incidence of spastic quadriplegic intellectual impairment is the highest type. Our findings indicated that the percentage of special children who received treatment for their uncorrected refractive errors, strabismus, amblyopia, and other eye diseases was significantly higher than that of ordinary school children, and the correction treatment rate was lower than that of ordinary children. Because most children cannot express independently, parents or guardians usually paied more attention to the physical development and learning ability but ignored the visual impairment. There were statistically significant differences in the subjective far vision, objective far vision, corrected vision, diopter, and near stereopsis acuity between the varying etiologies and degrees of mental retardation. In the aforementioned tests, there was no significant difference between different genders. The findings of the screening revealed that the majority of children with cerebral palsy who also had severe mental retardation and were caused by craniocerebral diseases had high levels of astigmatism and amblyopia. There was a significant difference in the children's subjective far vision, objective far vision, and near stereopsis acuity. Children of this nature require a heightened level of care.
In this study, children with CP and mental retardation exhibited poor expression ability and were unable to cooperate or communicate effectively. vision acuity result was only used as a reference; it was not the primary factor that was used to determine whether or not they had amblyopia. 15.91% of the children who were examined had an objective far vision of less than 20/40, which was significantly higher than that of normal children. About 5.26% of these children showed amblyopia-related risk factors. In addition, a considerable number of special needs children (10.65%) did not have any organic diseases in their eyes, the examination of the fundus optic nerve and pupil response to light were both normal, the improvement of corrected vision was not obvious, there were no amblyopia related risk factors, and there was insufficient evidence for the diagnosis of "amblyopia". Some experts believe that these children may have visual pathway damage, in a condition known as central visual impairment (CVI) [18]. CVI is now the most common cause of visual impairment in children in developed countries. According to the World Health Organization (WHO), the proportion of children in developing economies who are blind or have significant visual impairment as a result of anomalies in their central nervous systems can reach up to 20%[19]. In recent years, as a result of advancements in perinatal medicine, the survival rate of preterm infants has been increasing more than ever, and concurrently, the prevalence of CVI in developing countries is also increasing. The most common etiology of CVI in premature infants is ischemic and hypoxic encephalopathy, particularly brain nerve damage. The lesions primarily occurred in the posterior visual pathway lesions of the geniculate body and the related areas of the occipital visual cortex, which led to severe visual impairment or even blindness. Patients with CVI typically also suffer from a decline in their capacity to perceive visual ability, walking difficulties, social communication disorders, autism, and so on. According to their medical histories and the conditions that caused them, children who have intellectual disabilities are categorized as having premature asphyxia, congenital stupidity, birth injury, craniocerebral disease, and other unknown causes. As a consequence of this, it was hypothesized that certain children who have cerebral palsy in addition to mental retardation have poor vision due to the damage to the optic nerve pathway. We are unable to make a quick diagnosis of "amblyopia" without first inquiring about the patient's medical history, determining whether or not they are at risk for amblyopia, and performing a brain MRI.
In this study, the children's objective far vision measured by electrophysiological scanning VEP was lower than that of normal children of the same age who had amblyopia risk factors and organic lesions of the ocular structure excluded. Because the children who were examined might have been suffering from a central visual impairment, we were more cautious in the diagnosis of amblyopia in special children. The examination of children's subjective expression, such as visual acuity, was only used as a reference, and it was primarily combined with the objective visual acuity examination. Additionally, to diagnose amblyopia, it was necessary to observe whether it was combined with anisometropia, high ametropia, form deprivation, strabismus, and other amblyopia risk factors.
Due to the constraints of the conditions and the difficulty of certain examinations, such as the visual field examination, and because some of the children did not cooperate or effectively express themselves, we were unable to collect comprehensive data on the visual function of children with cerebral palsy and intellectual disabilities and investigate the causes of their poor visual function. In addition, this study focused on the Chaoyang District in Beijing. The economic status and medical conditions are superior to those in rural and mountainous areas, hence the sample may be susceptible to selection bias. Expanding the sample size, increasing the number of geographical options, and enhancing the number of inspections can yield more reliable data and findings. This study successfully examined the characteristics of visual function in eyes of children with cerebral palsy and intellectual disabilities in Chaoyang District in Beijing. It is recommended to screen, detect, and treat early to improve the visual function of children with low vision intellectual disabilities, enhance their learning and cognitive ability, improve their quality of life and independent survival ability, and enable them to be better integrated into society, thereby reducing the cost of family and social support and education. The screening of the eyes of children with cerebral palsy and intellectual disabilities reflects the care for children with special needs, which has a significant societal function. Screening for visual function in children attending special schools is simple and without side effects or risks. Therefore, it is worthy of nationwide dissemination.