Abstract
Purpose: :
To determine the relative stability of refractive error components in a longitudinal sample of Native American pre-school and school-aged children belonging to a tribe (the Tohono O'odham) having a high prevalence of corneal astigmatism.
Methods: :
We combined data from three studies (NEI/NIH EY11155 (JMM), NEI/NIH 13153 (EMH) and NEI/NIH EY08893 (JDT) that examined 3387 children 3 years or older using an identical cycloplegic autorefraction protocol (Retinomax K-Plus, Nikon, now Right Mfg). This longitudinal database was stratified into subjects having no/low (<1D) and high (≥ 1D) refractive astigmatism in the right eye at baseline. A mixed-model program (Stata Corp, Version 11 analysis routine xtmixed) was applied to this data to determine the comparative predictors of slope, indicating stability of refraction.
Results: :
At least one follow up examination was obtained on 2447 children. A total of 8481 refractions were obtained, with an average follow up of 2.65 years (SD 2.38, range = 0.23 to 11.25 years.) Dates of entry into the study ranged from 8/14/1997 - 5/17/2010. Average age at first measurement was 6.58 years (SD = 3.16, range = 3.00 - 16.3 yrs.) Average age at last follow-up measurement was 9.09 years (SD = 3.33, range = 3.49 - 17.07 yrs). Non-astigmatic children tended to remain non-astigmatic. The baseline refractive astigmatism of less than 1D decreased at a rate of -0.059 D/ Yr (p<0.0001). Astigmatism tended to decrease in the astigmatic children at a rate of -0.196 D/ Yr (p<0.001). The difference in rates between the two groups is statistically significant (p<0.0001).
Conclusions: :
A clinically small but statistically significant decrease in refractive astigmatism, averaging about 0.2 D/Yr, was observed among children having ≥ 1D refractive astigmatism at baseline. These data suggest that if a preschool or school-age Tohono O’odham child is screened and found to have little or no astigmatism they are likely to remain non-astigmatic. Conversely, if a child is found to require glasses for astigmatism, it is likely that they will continue to require eye care, for the rate of astigmatism regression is low.
Keywords: astigmatism • clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology • visual development: infancy and childhood