Glasses to prevent eye misalignment in far-sighted children

Review question
We compared the benefits and harms of wearing glasses to other interventions in far-sighted children to prevent the development of eye misalignment.

Background
Infants typically are born hyperopic, or far-sighted, and as they grow, their eyes typically grow to where they can see clearly. Some children, however, remain very far-sighted. Being far-sighted means that to focus on something up close the child must use a great deal of effort (called accommodation). This prolonged and repeated 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 eye misalignment (called strabismus), commonly known as crossed eyes. Strabismus makes it difficult for the eyes to work together to focus. Children who develop strabismus are then more likely than children without strabismus to develop amblyopia. Amblyopia, commonly known as lazy eye, is a condition where the child cannot achieve normal visual acuity (clear vision). Amblyopia requires treatment to prevent long-term vision loss; however, even the use of glasses may not allow a child with amblyopia to have 20/20 vision. Doctors often prescribe glasses to prevent the development of strabismus in far-sighted children, but very little research has been done on the effectiveness of this treatment.

Study characteristics
We identified results from three randomized controlled trials (RCTs; clinical studies where people are randomly put into one of two or more treatment groups) to determine whether glasses were successful in reducing the occurrence of strabismus in far-sighted infants. The trials enrolled infants ages 12 months or younger and measured outcomes between the ages of three and four years. The three trials enrolled 855 infants and included about 79% of the infants in the final analyses of different outcomes. These trials were all conducted in the UK with follow-up periods ranging from one to 3.5 years. The evidence is current up to April 2014.

Key results
Combining the results of the three trials, we found the risk of strabismus with wearing glasses is uncertain. We identified several potential biases in the way these three trials were conducted. Given the high risk of bias and amount of missing data, it is possible the observed decrease in risk of developing strabismus may be an overestimate of the true effect. The evidence does not currently support the conclusion that glasses prevent strabismus in far-sighted children. More research is required to answer the question. In addition, the prescription of glasses, particularly glasses that correct all of the prescription (full correction), may prevent eyes from developing naturally and normalizing to clear visual acuity. Emmetropization (normalization of vision which usually occurs during the natural growth process) was reported in two trials: one trial suggested that spectacles impede emmetropization, and the second trial reported no difference in the rate of refractive error change.

Quality of the evidence
The overall quality of the evidence was very low, particularly due to improper trial design, incomplete outcome data, and the lack of power to provide an accurate estimate of the overall treatment effect of spectacle correction for preventing strabismus.

Authors' conclusions: 

Although children who were allocated to the spectacle group were less likely to develop strabismus and less likely to have visual acuity worse than 20/30 children allocated to no spectacles, these effects may have been chance findings, or due to bias. Due to the high risk of bias and poor reporting of included trials, the true effect of spectacle correction for hyperopia on strabismus is still uncertain.

Read the full abstract...
Background: 

Hyperopia (far-sightedness) in infancy requires accommodative effort to bring images into focus. Prolonged accommodative effort has been associated with an increased risk of strabismus (eye misalignment). Strabismus makes it difficult for the eyes to work together and may result in symptoms of asthenopia (eye strain) and intermittent diplopia (double vision), and makes near work tasks difficult to complete. Untreated strabismus may result in the development of amblyopia (lazy eye). The prescription of spectacles to correct hyperopic refractive error is believed to prevent the development of strabismus.

Objectives: 

To assess the effectiveness of prescription spectacles compared with no intervention for the prevention of strabismus in infants and children with hyperopia.

Search strategy: 

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 4), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to April 2014), EMBASE (January 1980 to April 2014), PubMed (1966 to April 2014), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 3 April 2014. We also searched the Science Citation Index database in September 2013.

Selection criteria: 

We included randomized controlled trials and quasi-randomized trials investigating the assignment to spectacle intervention or no treatment for children with hyperopia. The definition of hyperopia remains subjective, but we required it to be at least greater than +2.00 diopters (D) of hyperopia.

Data collection and analysis: 

Two review authors independently extracted data using the standard methodologic procedures expected by The Cochrane Collaboration. One review author entered data into Review Manager and a second review author verified the data entered. The two review authors resolved discrepancies at all stages of the review process.

Main results: 

We identified three randomized controlled trials (855 children enrolled) in this review. These trials were all conducted in the UK with follow-up periods ranging from one to 3.5 years. We judged the included studies to be at high risk of bias, due to use of quasi-random methods for assigning children to treatment, no masking of outcomes assessors, and high proportions of drop-outs. None of the three trials accounted for missing data and analyses were limited to the available-case data (674 (79%) of 855 children enrolled for the primary outcome). These factors impair our ability to assess the effectiveness of treatment.

Analyses incorporating the three trials we identified in this review (674 children) suggested the effect of spectacle correction initiated prior to the age of one year in hyperopic children between three and four years of age is uncertain with respect to preventing strabismus (risk ratio (RR) 0.71; 95% confidence interval (CI) 0.44 to 1.15; very low quality evidence). Based on a meta-analysis of three trials (664 children), the risk of having visual acuity worse than 20/30 at three years of age was also uncertain for children with spectacles compared with those without spectacle correction irrespective of compliance (RR 0.87; 95% CI 0.60 to 1.26; very low quality evidence).

Emmetropization was reported in two trials: one trial suggested that spectacles impede emmetropization, and the second trial reported no difference in the rate of refractive error change.

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