The results of epidemiological studies of strabismus have shown that the prevalence of strabismus among different populations varies by region and ethnicity. The prevalence of strabismus among white and African American children from 6 to 71 months was 3.3% and 2.1%, respectively. Esotropia and exotropia accounted for half the strabismus cases. These were 3.55% and 3.24%, respectively, among Asian and non-Hispanic white children. Strabismus was found to be higher in children aged 6–72 months. In Singapore, the prevalence of strabismus among children aged 6–72 months was found to be 0.80%, and the ratio of exotropia to esotropia was 7:1, with 63% of exotropia being intermittent. Among 2704 patients with horizontal strabismus in Hong Kong, exotropia was shown to be more common than esotropia. In addition, the proportion of patients with intermittent exotropia seemed to be increasing. Meanwhile, paralytic strabismus was the most common strabismus among adults. Esotropia is most common strabismus in the first 10 years of life, and a population-based study found that accommodative and acquired nonaccommodative forms of childhood esotropia occur most frequently. Intermittent exotropia and insufficient convergence are the most common forms of childhood exotropia. The results of this study showed that exotropia accounted for the highest proportion of all strabismus cases at 63.5%, followed by esotropia at 13.2%. The ratio of exotropia to esotropia was thus 5:1. There are several reasons that could explain this result: (1) The incidence of different types of strabismus may be related to race, genetics and refractive errors. It has been reported that prematurity and maternal smoking during pregnancy are associated with a higher risk of paediatric esotropia and exotropia. Furthermore, strabismus was associated with gestational age, hyperopic refractive error and astigmatism. Esotropia, with lower gestational age and a heavier placenta; exotropia, with a maternal history of previously treated hypertension and maternal use of recreational drugs during early pregnancy. (2) Early screening of children’s vision and binocular visual function is associated with the incidence of exotropia. Early vision screening provides an opportunity for intermittent exotropia to be detected, which increases the diagnostic levels of the disease. (3) The choice of surgery timing on the basis of the characteristics of the disease could play an important role. Most children with esotropia have refractive errors and amblyopia. Both early precision optics and improved eye adjustment function have a corrective effect on the eye position in esotropia, which can reduce the need for surgical intervention. Contrarily, surgery is the primary treatment for patients with exotropia. Early strabismus surgery could not only reduce the damage to binocular visual function caused by strabismus, but also facilitate the establishment of visual function after surgery.
Intermittent exotropia is the most common type of exotropia, accounting for 50–90% of all patients with exotropia. The results of this study showed that intermittent exotropia makes up the highest proportion (71.3%) of all patients with exotropia. Furthermore, exotropia constitutes the highest proportion of all strabismus patients. It can be speculated that surgery for intermittent exotropia is currently the main type of strabismus surgery. In this study, the main surgical group of intermittent exotropia patients comprised preschool and primary school-aged children, and the basic type was the main type of intermittent exotropia. The number of strabismus patients was relatively stable each year from 2014 to 2016, but gradually increased annually over the 2017–2019 period. This reason for this can be explained as follows: Many patients or the parents of children understand and receive early strabismus treatment because of a concomitant improvement in the national quality of life and awareness of strabismus. Adult patients were the main population of patients who underwent reoperation, which may be related to the high recurrence rate of strabismus over time. Esotropia was the highest form of strabismus and exotropia the lowest in patients aged 0–6 years, and this may be related to esotropia often being associated with hyperopic refractive abnormalities. Furthermore, exotropia may be related to the occurrence and development of myopia.
It was found that patients with intermittent exotropia are at a great higher risk of visual fatigue in comparison with healthy individuals. Strabismus patients showed a greater risk of developing thoracic scoliosis.The temporal integration for stereopsis is impaired in patients with IXT, requiring longer critical integration time to achieve elevated optimal stereoacuity.Children with untreated strabismus can develop impaired binocular vision, which can interfere with their ability to conduct social interactions with other children. Lack of binocularity and stereopsis in children is associated with significant motor skills impairment, in particular for static balance and catching tasks. Children can subsequently develop a sense of inferiority and fail to lead normal lives. Both the child and their parents' HRQOL showed a trend toward correlating with clinical severity[17, 18]. Strabismus surgery has a positive impact on children’s physical and psychological functioning. Children with greater corrections experience greater improvements in their quality of life after surgery.The stereopsis and HRQOL in adults with childhood large angle exotropia can be improved after successful surgical correction. At the same time, with improvements in the national quality of life and awareness of children’s diseases, many parents of children with strabismus understand and accept that early treatment of strabismus can enable children to obtain good stereo vision. Importantly, populations with strabismus need early treatment. This study showed that, among the patients who underwent strabismus surgery, those at primary school level (i.e. 7–12 years old) comprised the largest group, while those at preschool and primary school level (i.e. aged 0–12 years) accounted for 60% of all patients who underwent strabismus surgery. The parents of children in the latter age group should choose early strabismus surgery. In addition to being concerned that strabismus may cause damage to binocular visual function, some parents also worry about the impact of strabismus on the normal psychological development of their children.
With improvements in living standards, the prevention and treatment of strabismus and amblyopia have gradually been carried out in various parts of China, and emphasis has been placed on children’s diseases and the need for early interventions. Many children with strabismus in relatively economically developed areas are screened and treated in hospitals. In addition, with the continuous improvements in ophthalmologists’ technical levels, the treatment of strabismus has become more professional, which has increased the probability of successful surgery. In areas with relatively less-advanced medical standards where there are a lack of professional ophthalmologists, some ophthalmologists have relatively little knowledge of strabismus or do not pay enough attention to the disease. They believe that strabismus surgery should be provided when the child is older, thus giving patients the wrong information and causing problems. These children miss the optimal time for surgery, impairing their binocular vision and/or missing the best age to establish binocular vision. At the same time, because of the economic prosperity in China, excessive medical treatment of strabismus and amblyopia has become a prominent, negative medical phenomenon. Excessive medical treatment of strabismus includes violations of treatment standards and expanded operative indications. Accordingly, every ophthalmologist should master the standardised operative indications for strabismus. Promotional efforts and education about strabismus should not only be carried out in hospitals, but also in communities and schools so that every citizen can acquire a certain level of knowledge of strabismus. At the same time, ophthalmologists should perform eye examinations on preschool children so that children with strabismus can be detected early.