Longitudinal Change in Astigmatism in Adolescent Australian Schoolchildren

Abstract

Purpose : To investigate 5-year change in refractive (RA), corneal (CA) and internal (IA) astigmatism in a cohort of Australian schoolchildren.

Methods : The Sydney Myopia Study (SMS) examined a population-based random cluster sample of children aged 12 (n=2353) from 21 secondary schools, with a 5-year follow-up (52%) at 17 years. A comprehensive examination included cycloplegic autorefraction (cyclopentolate 1%, Canon RK-F1) and ocular biometry. RA and CA were defined as ≤-1.00 dioptres (D) based on right eye data. Vectors were calculated, with +J₀ corresponding to with-the-rule (WTR), -J₀ against-the-rule (ATR), and J₄₅ to oblique astigmatism. IA was the vector difference between RA and CA. Baseline spherical equivalent refraction was categorised as myopia ≤-0.50D, emmetropia >-0.50 to <+2.00D and hyperopia ≥+2.00D. The study adhered to the tenants of the Declaration of Helsinki.

Results : The prevalence of RA increased from 7.7% to 9.6% (p<.001), with a parallel increase in prevalent CA from 28.2% to 36.0% (p<.001). There was no significant change in mean RA cylinder power (p=0.25), despite a significant increase in mean CA power (p<.001). When stratified by baseline refractive error, there was an increase in mean power of CA in all groups (all p<0.035) but, a significant increase in mean RA power was present for children with baseline myopia only (p=0.001). Mean refractive J₀ shifted from -0.024 to 0.041 (p<.001) reflecting an increase in WTR astigmatism. This was related to an increase in CA J₀ towards WTR (mean; baseline 0.32, follow-up 0.38 p<.001) and a slight decrease in ATR IA J₀ (mean; baseline -0.35, follow-up -0.34 p<.001). This trend towards more positive IA vectors (J₀ and J₄₅) was present in all refractive groups but, only significant for children with baseline emmetropia (p=0.011 and p<.001, respectively). There was a significant negative correlation between CA and IA vector change (J₀ -0.63, p<.001, J₄₅ -0.72, p<.001), that was present for all refractive groups.

Conclusions : Ongoing changes to astigmatism occur throughout adolescence, with uniform increases in CA across all refractive groups. The negative correlation between CA and IA vector change implies active compensation for CA. However, the trend towards reduced mean IA suggests that CA increases may be only partially offset. Variation in change between refractive groups may relate to lenticular changes occurring through adolescence.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.