Evaluation of refraction in a statistically significant sample: changes according to age and strabismus

Abstract

Purpose: To assess possible refractive changes according to age and strabismus in a statistically significant cohort.

Methods: A population-based sample of 12,534 subjects 0.5 to 20 years old, examined between 2004 and 2006, was tested. Each subject received a complete orthoptic examination, including spherocylindrical streak retinoscopy in cycloplegia. Patients were divided into those with orthophoria (7,784) and those with strabismus (4,750), and the latter group was further divided into those with esodeviation (3,026) and those with exodeviation (1,724). A statistical analysis of the spherical equivalent, astigmatism, and anisometropia was performed with an independent samples t test or one-way analysis of variance.

Results: The percentage of patients with a mean spherical equivalent within +/- 1 and +/- 2 standard deviations was greater than 68% and 95%, respectively. The mean spherical equivalent of the total sample was 1.62 diopters (D) (+/- 2.88). The mean spherical equivalent was 1.10 +/- 2.94 D in the orthophoria group, 3.22 +/- 2.29 D in the esodeviation group, and 1.13 +/- 2.50 D in the exodeviation group (one-way analysis of variance; P = .000). Age-related changes in the mean spherical equivalent showed a clear and steady myopic shift, reaching mean myopic refraction at 12 to 14 years in both the total sample and the orthophoria and exodeviation groups. It assumed a more constant trend, with no myopic swing, in the esodeviation group (P = .000). Mean astigmatism was less in patients with less than 1.00 D anisometropia (0.83 +/- 0.92 D) than in those with 1.00 D or greater anisometropia (1.42 +/- 1.18 D) (t test; P = .0001).

Conclusion: Both the age-related trend in the spherical equivalent and the high hyperopic values of the distribution peak in patients with esodeviation confirm the importance of the hypermetropic refractive component. The statistically significantly higher incidence of astigmatism in patients with 1.00 D or greater ametropia highlights its incidence in amblyopia.