Abstract
Purpose :
Examine the impact of refractive error on incident strabismus in Australian schoolchildren.
Methods :
The Sydney Myopia Study followed two cohorts after 5-6 years; 876 younger children (aged 6 to 12 years) and 1211 older children (12 to 17 years). All children received comprehensive ocular examinations. Orthoptic assessment identified intermittent exotropia based on an outward deviation on cover test and evidence of stereopsis. Cycloplegic autorefraction (cyclopentolate 1%; Canon RK-F1; Canon, Tokyo, Japan) was used to identify spherical equivalent myopia ≤-0.5 dioptres and hyperopia ≥+3.0 dioptres. Ethical approval was obtained, and the study adhered to the tenets of the Declaration of Helsinki. Chi-Square was used to determine differences in the proportion of children with strabismus between baseline and follow-up, according to the type of refractive error at baseline. Incidence rates were calculated from the number of children without strabismus at baseline and who had a strabismus at follow up.
Results :
The incidence rate of strabismus was 8.0/1000 children per year in the younger cohort and 16.3/1000 children per year in the older cohort. There were significant changes in the type of strabismus present in the two cohorts over the follow-up period (younger cohort, p<0.0001 and older cohort, p=0.025). Of the children without any strabismus at baseline, intermittent exotropia was the most common type of strabismus to develop, with 1.9% of the younger cohort and 2.2% of the older cohort developing an intermittent exotropia by follow-up. In the younger cohort, 25.0% of myopic children developed a strabismus, compared to 1.9% of emmetropic and 4.3% of hyperopic children (p<.0001). In these children with early onset myopia, all incident strabismus was intermittent exotropia type. This estimates an incident rate for intermittent exotropia at 45.5/1000 children per year in those with early onset myopia. This trend was less evident in the older cohort as incident strabismus was not significantly associated with refractive error (p=0.91). In the older children with myopia, only 4.2% developed strabismus and the incident rate of intermittent exotropia in these myopic children was 6.6/1000 children per year.
Conclusions :
This study highlights the significant relationship between refraction and strabismus, with the age of myopia onset being an influential factor in the development of intermittent exotropia.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.