Abstract
Purpose :
While there have been reports indicating a notable link between astigmatism and myopia development, the impact of astigmatism on different ametropic conditions remains largely unexplored. This study aimed to investigate how the progression rate of axial length (AL) and spherical equivalent (SE) varies across different types of astigmatism and ametropic conditions.
Methods :
This is a longitudinal study conducted annually from 2018 to 2022 in seven primary and secondary schools in Tianjin, China. It involved vision screenings, with non-cycloplegic refraction and AL measured using autorefractors and Lenstar, respectively. The study included subjects aged 5 to 16 years with astigmatism ≤ -0.50D at the outset. Exclusion criteria included a history of contact lens and ortho-k use, or any shift in type of astigmatism during follow-up. Subjects were categorized by axis of astigmatism (with-the-rule [WTR], against-the-rule [ATR], oblique) and baseline ametropia along principal meridians, defined as hyperopia (neither meridian nearsighted), mixed (one meridian farsighted and the other nearsighted), and myopia (neither meridian farsighted). The progression rates of AL and SE were estimated by regression on each subject's data. ANCOVA test was used to compare AL and SE progression across groups, controlling for age, follow-up period, baseline cylinder, and AL or SE. Only data from right eyes were used.
Results :
Data from 5919 eyes were analyzed (WTR, n=4776; Oblique, n=489; and ATR, n=654), with a mean age of 9.5±2.5 and follow-up of 2.6±1.0 years. The mean progression rates of AL and SE were 0.30±0.43 mm/year and -0.40±0.56 D/year, respectively. Overall, significant differences in AL (P<0.001) and SE (P=0.006) progression were found across different types of astigmatism, with ATR showing a higher AL and SE progression than WTR (Bonferroni P<0.01). In ametropic subgroups, significant difference in AL or SE progression (both P<0.05) across astigmatism types was observed in myopic eyes, but not in mixed and hyperopic eyes.
Conclusions :
The initial axis of astigmatism plays a crucial role in the progression of AL and SE in children of school age, thereby impacting their refractive development. However, this impact is not consistent and varies with the initial ametropic conditions. In particular, ATR astigmatism was linked with an increase in axial length and a more pronounced shift towards myopia in myopic eyes.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.