What was the aim of this review?
To find out if wearing eyeglasses by far-sighted children will prevent crossed eyes (strabismus) and associated effects from developing.
The evidence does not currently support the conclusion that eyeglasses prevent strabismus in far-sighted children, or that wearing glasses prevents lazy-eye (amblyopia). This evidence was limited due to some parts of the studies not being done as well as they could and small number of study participants.
What was studied in the review?
Infants typically are born far-sighted, meaning they only have clear vision at distance. As children grow, their eyes also grow to where they can see clearly at both near and far distances. About 9% of children remain very far-sighted. Being far-sighted means that to focus on something up close the child must use a great deal of effort. This effort can cause symptoms, such as headaches, seeing double, and eyestrain, as well as cause difficulty doing things up close, such as reading. Children that remain far-sighted are more likely than children with normal vision to develop crossed eyes (strabismus), which may happen in 3.5% to 5.7% of children, or 10% to 20% of children with high levels of far-sightedness. Strabismus makes it difficult for the eyes to work together to focus. It is thought that about 50% of children with strabismus develop amblyopia, meaning a child cannot get clear vision even when using glasses. Depth perception, or how two things are related to each other in space, is often affected as well. Doctors often prescribe eyeglasses to prevent the development of strabismus and these other associated problems in far-sighted children, but it is unclear whether the glasses themselves may prevent the eyes from growing normally.
What were the main results of the review?
We identified results from four randomized controlled trials (clinical studies where people are randomly put into one of two or more treatment groups) to determine whether eyeglasses were successful in preventing strabismus in far-sighted infants compared with no eyeglasses. The trials enrolled infants aged six months to less than 36 months and measured outcomes between the ages of three and four years. The four trials enrolled 985 infants. We found unclear evidence of a difference between the two groups in how often strabismus occurred over the follow-up period. We also found unclear evidence on whether the prescription of eyeglasses affected depth perception or prevented eyes from developing naturally to clear vision. We have low confidence in these findings because some parts of the studies were not done well and the small number of children in the studies.
How up-to-date is this review?
The effect of spectacle correction for prevention of strabismus is still unclear. In addition, the use of spectacle on the risk of visual acuity worse than 20/30, amblyopia, and inadequate emmetropization is also unclear. There may be a benefit on prevention of inadequate stereoacuity. However, these effects may have been chance findings or due to bias.
Hyperopia in infancy requires accommodative effort to bring images into focus. Prolonged accommodative effort has been associated with an increased risk of strabismus. Strabismus may result in asthenopia and intermittent diplopia, and makes near work tasks difficult to complete. Spectacles to correct hyperopic refractive error is believed to prevent the development of strabismus.
To assess the effectiveness of prescription spectacles compared with no intervention for the prevention of strabismus in infants and children with hyperopia.
We searched CENTRAL (2018, Issue 12; which contains the Cochrane Eyes and Vision Trials Register); Ovid MEDLINE; Embase.com; three other databases; and two trial registries. We used no date or language restrictions in the electronic search for trials. We last searched the electronic databases on 4 December 2018.
We included randomized controlled trials and quasi-randomized trials investigating spectacle intervention or no treatment for children with hyperopia. We required hyperopia to be at least greater than +2.00 diopters (D).
We used standard Cochrane methodological procedures. The primary outcome was the proportion of children with manifest strabismus, as defined by study investigators. Other outcomes included the amblyopia, stereoacuity, and the effect of spectacle use of strabismus and visual acuity. We also collected information on change in refractive error as a measurement of the interference of emmetropization.
We identified four randomized controlled trials (985 children enrolled who were aged six months to less than 36 months) in this review. Three trials were in the UK with follow-up periods ranging from one to 3.5 years and one in the US with three years' follow-up.
Investigators reported both incidence and final status regarding strabismus. Evidence of the incidence of strabismus, measured in 804 children over three to four years in four trials was uncertain although suggestive of a benefit with spectacle use (risk ratio (RR) 0.65, 95% confidence interval (CI) 0.41 to 1.02). We have very low confidence in these results due to high risk of bias, inconsistency, and imprecision. When assessed as the proportion of children with strabismus at the end of three years' follow-up, we found a similar level of evidence for an effect of spectacles on strabismus as reported in one study (RR 1.00, 95% CI 0.31 to 3.25; 106 children). We have very low confidence in these results because of low sample size and risk of bias.
One trial reported on the risk for developing amblyopia and inadequate stereoacuity after three years in 106 children. There was unclear evidence for a decreased risk of developing amblyopia (RR 0.78, 95% CI 0.31 to 1.93), and limited evidence for a benefit of spectacles for prevention of inadequate stereoacuity (RR 0.38, 95% CI 0.16 to 0.88). We have very low confidence in these findings due to imprecision and risk of bias.
The risk of not developing emmetropization is unclear. One trial reported on the proportion of children not achieving emmetropization at three years' follow-up (RR 0.75, 95% CI 0.18 to 3.19). One trial suggested spectacles impede emmetropization, and one trial reported no difference. These two trials could not be combined because the methods for assessing emmetropization were different. With the high risk of bias and inconsistency, the certainty of evidence for a risk for impeding or benefiting emmetropization is very low.
Based on a meta-analysis of four trials (770 children), the risk of having visual acuity worse than 20/30 measured up to three years of age or at the end of three years of follow-up was uncertain for children with spectacle correction compared with those without correction (RR 0.87, 95% CI 0.64 to 1.18; very low confidence due to risk of bias and imprecision).