Pattern distribution of strabismus surgery patients
The data of 5746 strabismus patients who visited Qingdao Eye Hospital from January 2014 to December 2019 were recorded and analysed. The patients’ ages ranged from 1 to 84 years, with an average age of 15.2 years. The horizontal strabismus angle was 0–160 PD, and the vertical deviation was 0–90 PD. Among the patients, 6.3% (364/5746) had an anterior segment abnormality, and 2.3% (130/5746) had a posterior segment abnormality. The number of strabismus patients was relatively stable each year from 2014 to 2016 (833, 843, 853, respectively) but gradually increased each year from 2017 to 2019 (971, 1039, 1207, respectively) (Fig 1). In terms of gender, 51.7% (2868/5746) were male, and 48.3% (2778/5746) were female. There was no significant difference between the gender composition over time ( P=0.146) (Table 1).
The strabismus patients resided in three areas: within Qingdao, outside Qingdao(within Shandong Province) and outside Shandong Province. The statistical results over the 6-year study period showed that the majority of the patients were from Shandong Province: 47.5% (2730/5746) of the patients were from Qingdao, 42.3% (2429/5746) were from other cities in Shandong Province and 10.2% were from other provinces (587/5746) (Table 1).
The patients were divided into four age groups: 0–6 years (preschool level), 7–12 years (primary school level), 13–18 years (middle school level) and over 18 years (adults). The statistical results of the constituent ratio of age showed that 9.3% (534/5746) of the patients were 0–3 years old, 27.6% (1587/5746) were 0–6 years old, 32.4% (1860/5746) were 7–12 years old, 12.2% (700/5746) were 13–18 years old and 27.8% (1599/5746) were over 18. There were significant differences between the age groups over time (P=0.021). Among the patients with strabismus, the 7–12-year-olds (primary school level) comprised the largest group, followed by those who were over 18 (adults). The patients under 12 years (preschool and primary school level) accounted for 60.0% (3447/5746) of all the strabismus patients (Table 1).
All the categorisations were based on the classification of strabismus formulated by the Strabismus and Paediatric Ophthalmology Group of the Ophthalmology Branch of Chinese Medical Association. Among the patients, the majority (63.5%, 3650/5746) had exotropia, followed by esotropia and vertical rotational strabismus at 13.2% (758/5746) and 9.7% (555/5746), respectively. Intermittent exotropia was the most common type of exotropia, accounting for 71.3% (2604/3650) of patients. Special types of strabismus made up 6.3% (360/5746) of the patient population. Among these, the most common type was dissociated vertical deviation (DVD), which accounted for 87.5% (315/360). A-V strabismus, nystagmus and central paralytic strabismus comprised a small proportion of the patients in this study at 4.1% (236/5746), 1.9% (112/5746) and 1.3% (75/5746), respectively. Among all the patients, the exotropia group was the largest, and intermittent exotropia was the most common type of exotropia. The differences in the types of strabismus became statistically significant as time passed (P=0.000). The rate of esotropia was 11.3% (286/2529) from 2014 to 2016 and increased to 14.7% (472/3217) during 2017–2019. Meanwhile, the rate of exotropia was 66.8% (1689/2529) from 2014 to 2016 but decreased to 61.0% (1961/3217) during the period 2017–2019 (Table 1).
Pattern distribution of intermittent exotropia
Intermittent exotropia was the most common type of exotropia in this study, so the gender composition, constituent ratio of age and types of strabismus of the 2604 intermittent exotropia cases were analysed statistically. The results showed that 50.8% (1322/2604) of the patients were male, and 49.2% (1282/2604) were female. There was no significant difference between the two groups in terms of gender (P=0.054). The statistical results of the constituent ratio of age showed that 29.8% (775/2604) of the patients were 0–6 years of age. Among them, 10.2% (265/2604) were under 3 years of age, 19.6% (510/2604) were 4–6 years old, 42.9% (1117/2604) were 7–12 years old, 12.4% (322/2604) were 13–18 years old and 15.0% (390/2604) were over 18. There were no significant differences between the different age groups as time passed (P=0.303). Among the patients with strabismus, the primary school level patients (7–12 years old) comprised the largest group, followed by the preschool level patients (0–6 years old). Meanwhile, patients under 12 years of age (preschool and primary school level) accounted for 72.7% (1892/2604) of all patients, among whom 62.5% (1627/2604) were 4–12 years old. Intermittent exotropia was classified into the basic type, the convergence insufficiency type and the divergence-excess type, and these accounted for 79.8% (2077/2604), 12.1% (314/2604) and 5.3% (213/2604), respectively, of the intermittent exotropia patients in the study, with the basic type thus the most prevalent form. The differences between the three types over the 6-year study period were statistically significant over time (P=0.004) (Table 2).
Pattern distribution of strabismus patients undergoing reoperation
Four percent (231/5746) of all the patients required reoperation. Among them, 43.7% (101/231) were male, and 56.3% (130/231) were female. The majority, 88.3% (204/231), were from Shandong Province. The proportion of patients aged over 18 was 54.5% (123/231), which was the highest percentage among all the age groups. On the other hand, the proportion of patients aged 0–6 years was 3.5% (8/231), which was the lowest proportion among all the age groups. Adult patients were the main population group who underwent reoperation (Table 3).
Characterisation of strabismus classification at different ages
We analysed the ratios of the different types of strabismus among the four age groups. Esotropia was highest among patients aged 0–6 years (19.7%, 312/1587), while exotropia was lowest among patients aged 0–6 years (51.5%, 817/1587). The highest proportion of patients with vertical rotatory strabismus was those aged 0–6 years at 14.5% (230/1587). We calculated the proportion of patients with congenital strabismus in the age group of 0-6 years. Among them, the proportion of congenital esotropia was 8.5%(135/1587), while the proportion of congenital exotropia was 9.2%(147/1587) .The highest proportion of patients with central paralytic strabismus comprised those older than 18 years (3.7%, 59/1597), while the lowest proportions were patients aged 0–6 years and 7–12 years at 0.3% (4/1587 and 6/1860, respectively). The differences in the types of strabismus were statistically significant as time passed among the patients aged 0–6 years and older than 18 years (P=0.000; P=0.001, respectively). The rates of esotropia for these groups were 16.8% (115/683) and 10.6% (80/755), respectively, during the period 2014–2016 and increased to 21.8% (197/904) and 16.9% (142/842), respectively, from 2017 to 2019. Among the patients aged 0–6 years and older than 18 years, the rates of exotropia were 58.3% (398/683) and 68.9% (520/755), respectively, from 2014 to 2016, but these decreased to 46.3% (419/904) and 63.8% (537/842), respectively, during the 2017–2019 period. There was no statistical difference over time among the patients aged 7–12 years and 13–18 years (P=0.471; P=0.485, respectively) (Table 4; Fig 2).
Clinical risk factorsin 0-12 years old patients with exotropia and esotropia
The majority of the patients were under 12 years of age, among the patients, the majority had exotropia and esotropia, so we further analyzed the personal and family history of the strabismus patients under 12 years of age. Besides,we analyzed the correlation between the type of strabismus and the refractive state.The rate of premature delivery, oxygen inhalation, family history of Strabismus and eye diseases was higher in patients with esotropia(5.4%,25/463;3.9%,18/463;9.1%,42/463;7.8%,36/463) than exotropia(3.6%,75/2100;1.2%,25/2100;7.7,162/2100;4.2%,82/2100). Additionally,62.4%(289/463) of patients with esotropia showed hyperopia, while 7.3%(154/2100) of patients with exotropia showed hyperopia in refractive status. In contrast, 5.2% (24/463)of patients with esotropia showed myopia, while 39.9%(838/2100) of patients with exotropia showed myopia in refractive status. The rate of emmetropia in patients with exotropia(28.0%,587/2100) is significantly higher than in patients with esotropia(3.7%,17/463).(Table 5).