Baseline characteristics of children in the Early Glasses Study

Abstract

Purpose: The relationship between refractive error at age 1 and the risk of developing amblyopia or accommodative esotropia, and the protection offered by early glasses, is unknown. These are determined in the Early Glasses Study, a prospective, population-based, longitudinal, randomized controlled study. We report baseline findings.

Methods: Healthy children aged 12-18 months were recruited at Children's Healthcare Centres (CHCs) and received an entry orthoptic examination followed by cycloplegic retinoscopy. Children with amblyopia, strabismus, ophthalmic disease or very high refractive error were excluded. Those exceeding the AAPOS 2003 Criteria (> + 3.5D spherical equivalent (SE), > 1.5D astigmatism, > 1.5D anisometropia) were randomized into wearing glasses or not, and are followed-up by research orthoptists. Other children are followed-up by regular vision screening at CHCs and visual acuity is measured in all children at age 4.

Results: Parents of 865 children were called, 123 were excluded. Of 742 children enrolled, 601 underwent the entry orthoptic examination at age 14.5 ± 1.7 months. Mean SE was + 1.73 ± 1.18D, astigmatism -0.70 ± 0.44D, anisometropia 0.21D (IQR: 0-0.25). Of 62 (10.3%) children exceeding the Criteria, 52 were randomized into wearing glasses or not. Of 539 other children, 522 are followed up at CHCs. In total, 31 were excluded: 2 had strabismus and amblyopia, 7 strabismus, 2 amblyopia suspect, 1 strabismus suspect, 1 squinting during sinusitis, 4 excessive refractive error, 9 myopia, 2 ptosis, 1 oculomotor apraxia, 1 Duane syndrome, 1 congenital nystagmus.

Conclusion: Prevalence of strabismus (10/601) was as expected, but prevalence of amblyopia (2/601) was low, suggesting that common amblyopia develops later than generally thought.

Key messages: What is known High refractive errors cause amblyopia, but no study has determined the exact relationship between the kind and size of refractive error at age 1 and the risk to develop amblyopia, and assessed the protective effect of glasses in a controlled, population-based, longitudinal study. What is new At baseline, 601 children received a full orthoptic examination followed by retinoscopy in cycloplegia at the age of 14.5 ± 1.7 months; 10.3% had high refractive error exceeding spherical equivalent > + 3.5D, > 1.5D astigmatism, > 1D oblique astigmatism or > 1.5D anisometropia. The prevalence of amblyopia was lower (0.3%) than expected, suggesting that most amblyopia develops after the first year of life. The prevalence of anisometropia, associated with amblyopia in older children, was low (0.8%).

Keywords: Accommodative estropia; Amblyopia; Anisometropia; Astigmatism; Glasses; Hypermetropia.

Fig. 1

Flowchart from recruitment to Entry Orthoptic Examination and formation of three study groups. Children exceeding the Criteria (spherical equivalent >  + 3.5D, > 1.5D astigmatism, > 1D oblique astigmatism or > 1.5D anisometropia) were randomized into two groups, wearing glasses or not. Children not exceeding the Criteria continued vision screening as part of general screening at CHCs. All will have VA measured at 45 months using the same VA cards. Exclusion at each successive step is listed in white boxes on either side

Fig. 2

Distribution of spherical equivalent (SE) at 14.5 months. Mean SE of the most hypermetropic eye was + 1.84D (-2.50D to + 9.25D SD1.22), for the least + 1.63D (-3.00D to + 8.50D SD1.12)

Fig. 3

Distribution of astigmatism at 14.5 months

Fig. 4

Distribution of anisometropia at 14.5 months. At the age of 14.5 months anisometropia is rare

Fig. 5

Distribution of refractive errors found in children whose refraction exceeded the Criteria. Children with strabismus, amblyopia or very high refractive error were excluded (color)