Frequency of anisometropia in children and adolescents

Background: Our objective was to estimate the frequency of anisometropia at various educational stages, from pre-school to 9th school year, studying its association with gender, study cycle and area of residence. Methods: 749 children and adolescents (from 3 to 16 years old) participated in this study, 46.7% girls and 42.7% living in a rural environment. The refraction was performed with a paediatric, open field autorefractometer (PlusOptix), without cycloplegic and under binocular conditions. Results: The frequency rate of anisometropia in the studied sample was 6.1%, varying from 2.9% in pre-school education to 9.4% in the 3rd study cycle. Myopic anisometropia was the most frequent and hyperopic and astigmatic anisometropia showed identical proportions of occurrence. No statistical evidence was found to state that the occurrence of anisometropia differs between genders or between areas of residence. Regarding the school cycle, a significant association was found with spherical equivalent anisometropia, with an increase in its frequency with school progress (p=0,012), with myopic anisometropia being the main contributor to this variation. Conclusions: The increase in workload for near tasks has been identified as a risk factor for the increase in myopia. This fact may be related to the increase in anisometropia with the educational stage, found in this study. The high rate of anisometropia found in adolescents (9.4%) as well as the progressive increase in this rate throughout school progress (from 2.9% to 9.4%) suggests the need to extend the detection strategies of this condition to beyond childhood.