Environmental Factors and Childhood Vision; the Twins Eye Study in Tasmania

Abstract

Purpose: : To investigate the effect of early life environmental on visual acuity, refraction, strabismus and stereopsis in children.

Methods: : Twins and Triplets seen in the Twins Eye Study in Tasmania underwent an ophthalmic examination and retrospective questionnaire regarding sleeping behavior, crawling, walking, reading, television and computer use. A subset of these twins was also in the Tasmanian Infant Health Survey with prospectively collected data on antenatal smoking, gestation, birth weight and other factors.

Results: : The mean age the 346 individuals (172 multiple birth sets) at the time of examination was 9.25+2.4 years. Mean unaided visual acuity was 0.0 (6/6), with a mean refraction of +0.87, which decreased with increasing child age (p<0.01). Strabismus was found with 4.5% having esotropia/esophoria and 3.0% having exotropia/exophoria. Stereo testing found 4.1% saw nil on Titmus test and 5.8% saw nil on Lang test. Amblyopia was found in 4.6%. A prospective analysis, accounting for birth set clustering and relevant confounders found increasing levels of maternal smoking in the third trimester was associated with Lang test failure (p=0.001) and esotropia/esophoria (p=0.001), independently of postnatal infant smoke exposure to maternal smoking. Poor stereopsis on Titmus stereo test circles (<120 seconds of arc) was associated with late age of first crawling OR=1.23 (p=0.005) and late age of first walking OR=1.18 (p=0.001). After adjustment for maternal education and private health insurance and accounting for birth set clustering, the adjusted relative risk for poor convergence (<5cm) and reading difficulties was 2.35(1.04, 5.29).

Conclusions: : Antenatal smoking was independently associated with poor stereovision on Lang testing and esotropia/esophoria. This study adds to other work indicating visual function, not just acuity is likely to be important for reading. Further prospective investigation of the association between poor stereopsis and delayed walking is required. This may provide identification of high risk children for vision problems.

Keywords: strabismus: etiology • esotropia and exotropia • visual development