Accommodative instability predicts myopic progression in children
MedWire News: Results of a study in children suggest that instability of accommodation accompanies progression of early onset myopia.
The findings arise from a follow up of a previous investigation, where children with early-onset myopia were shown to have increased instability of accommodation compared with a group of emmetropic children. However, the study provided no evidence to determine the direction of causality.
To address this, Trine Langaas (Buskerud University College, Kongsberg, Norway) and Patricia Riddell (University of Reading, UK) assessed the children 2 years after their first examination.
At both examinations, accommodation was recorded using eccentric photorefraction while the children viewed targets set at three distances (accommodative demands): 0.25 m (4.00 D demand), 0.50 m (2.00 D demand), and 4.00 m (0.25 D demand).
In all, 13 myopic and 16 emmetropic children were included in the analysis.
Langaas and Riddell found that both refractive error and accommodative instability at the first examination highly correlated with the same measures at the second examination 2 years later.
The accommodative instability in the myopic participants for the 4.00 D target at the first examination ranged from 0.23 to 0.57 D, with a mean of 0.38 D, while the range for the emmetropic participants was 0.12 to 0.36 D, with a mean of 0.26 D. "Thus, the highest accommodative instability in the emmetropic participants was below the mean for the myopic participants," note the authors. Furthermore, no emmetrope became myopic during the course of the study.
Regression analysis revealed that instability of accommodation at the 4.00 D target during the first examination weakly predicted myopic progression. Indeed, greater myopic progression was found for children who had shown the greatest accommodative instability for the 4.00 target at the first examination.
Langaas and Riddell therefore suggest that decreased stability of accommodation may be one factor that might predict myopic progression. However, because the children were recruited after the onset of their myopia, the researchers note that they were unable to determine whether the accommodative instability preceded the myopia.
"Further research investigating stability of accommodation before the onset of myopia in a larger group of children with a wide range of myopia is required to verify our findings," they conclude in Clinical and Experimental Optometry.
By Nikki Withers