Controversies in pediatric refractive development
The development and treatment of refractive errors in children have been the subject of debate over many decades. Current theories on the emmetropization process, wherein the human visual system regulates the development of refractive error, point toward the first 18 months of life. Data indicates a trend toward low hyperopia by 12 to 18 months of life, regardless of the newborn’s refractive starting point.1
Stability in refractive error is evident between the ages of 2 to 5 years with a trend toward hyperopic regression.2 Beyond age 6, the progression of myopia has become a clinical concern.
Clinical controversies arise when discussing the management of pediatric refractive errors-the most basic is how often should refractive errors be measured/monitored and for which age groups. Also, when should correction for these refractive errors be prescribed, and what consequence does prescribing have on refractive error development? Finally, is not intervening an option for best acuity or best binocular development?
From a clinical management perspective, consider these controversies in the following three age groups: infant (0 to 18 months), toddler (2 to 5 years) and childhood (6 to 14 years). Consider normal refractive development in each age group and what to do when normal refractive development does not occur or when the visual system shows signs of distress with the refractive error it has.
Related: How to control myopia progression in your practice
Infant (Birth to 18 months)
For the infant eye, the process of emmetropization may be linked to the accommodative system.
If, for example, the 3-month-old has a high hyperopic refractive error, the “extra” accommodative effort to maintain a clear retinal image may, through an accommodative signal, alter the axial length growth to compensate.
In a three-month-old with a myopic refractive error, the lack of accommodative effort may signal the eye to stop the axial elongation process, allowing the refractive error to reach low hyperopia by 18 months.
If this is the case, then clinically, the refractive error in this age group may be constantly changing and would need close monitoring, such as cycloplegic refractions at four- to six-month intervals, up until age 18 months.
Animal models have shown an induced refractive error (through wearing glasses designed to create blur) results in changes to the axial length, adapting to the new induced refractive error.2
Is the same true when prescribing glasses for human infants during the emmetropization process? Does prescribing glasses interrupt the emmetropization process?
Related: How hyperopes differ from myopes
Now consider signs of visual distress, such as strabismus or nystagmus, and the visual system’s abnormal emmetropization.
Perhaps the abnormal emmetropization is secondary to an abnormal visual system. Does the provider prioritize emmetropization or visual development?
Children born prematurely (<31 weeks, <1500 g) have a risk of developing retinopathy of prematurity (ROP), and, depending on the severity of the disease, may require treatment with laser photocoagulation. As a result of laser treatment and the abnormal formation of the premature eye, these patients often develop significant myopia in the first six to nine months of life, which may need correction for proper visual development. In contrast, early studies using avastin for ROP treatment do not show a myopic shift. However, these studies are targeting a specific (milder) stage of ROP.4
Is prescribing for the clinically significant myopia controversial? Is there a risk of interfering with the emmetropization process, or has the ROP and/or treatment disrupted this process already, leaving the visual system vulnerable to unchangeable refractive errors for which the clinician must intercede?
Related: OCT in pediatric eye disease
Clinical examples
Consider the nine-month-old, former premature infant with ROP, post laser treatment, with a refractive error of -6.50 D in each eye. Although the infant’s visual demand at this stage of life is mostly near, prescribing for this myopic refraction is needed to stimulate proper visual development and proper accommodative demand/response to near targets.
Consider the seven-month-old with moderate hyperopia (+7.50 D OU) manifesting an esotropia of 30 prism diopters. When the refractive error was corrected, the esotropia was controlled, indicating this esotropia was early onset accommodative esotropia.
In these two cases, the visual system demonstrated distress with its uncorrected refractive condition and responded positively when compensated.
Does this compromise the emmetropization process? If so, is the preservation of vision and binocularity a fair trade for having to wear glasses for long term?
Infant summary
The emmetropization process appears to be an active process based on accommodative feedback which helps regulate and guide the infant visual system toward a refractive error of low hyperopia by age 18 months.
Atypical refractive errors need close monitoring through cycloplegic refractions. If the refractive error is creating distress that compromises visual or binocular development, then correction of the refractive error should be considered without worry to the emmetropization process outcome.
Related: Treating refractive error with corneal cross-linking
Toddler (2 to 5 years)
If the emmetropization process is successful, the toddler should have a refractive error of low hyperopia. The resultant (residual) refractive error may lead to visual compromise.
Consider the toddler with a refractive error of +5.00 D whose visual demand increases with age. Uncorrected hyperopia of this magnitude could lead to accommodative esotropia or bilateral amblyopia (if the visual system trades clarity in favor of low accommodative response). Evidence suggests moderate uncorrected hyperopia (>+3.50 D) can lead to difficulties learning in the classroom.5
Hyperopia in moderate to high amounts may lead to the development of accommodative esotropia. Hyperopia in patients with accommodative esotropia seems to regress less with some studies showing hyperopic regression of 0.10 D per year.6,7
Is this because of interference with emmetropization? Or is this a different model of the visual system that we do not fully understand?
If a toddler has developed anisometropia, consider prescribing because there is little evidence of this disrupting refractive error development. In fact, moderate amounts of anisometropia can lead to amblyopia in this age group and must be treated.
Myopia in this age group (>3.00 D) may represent a disruption in the emmetropization process but most likely does not represent incomplete emmetropization. Prescribing for myopic refractive errors in this age group allows for clear distance vison and for the accommodative demand/response to begin development.
Related: Examining 7 options to control myopia
Toddler summary
The active process described as emmetropization appears to be complete by age 18 months. In patients age 2 to 5 years, treatment for the refractive error can be performed without worry of interruption of this process. Prescribing for refractive errors that create visual distress, amblyopia, or the development of accommodative esotropia is essential for this age group.
While there is a trend toward regression of hyperopia in toddlers, keep in mind patients with accommodative esotropia regress 0.10 D per year on average.6 Refractive errors in toddlers are more predictable and can often be evaluated annually.
Related: How to build a myopia control practice
Childhood (5 to 13 years)
An ongoing controversy in managing childhood refractive errors is the concept of regulating the progression of myopia development. Many treatment strategies have been suggested over the years, with the most current evidence-based interventions being atropine, multifocal contact lenses, corneal reshaping with orthokeratology lenses, and outdoor time.8
In all treatment models, myopia continues to progress,but at a slower rate than if no treatment was performed. Myopia progression rates have been reported to be approximately 1.00 D per year.9
Many interventions show a trend for limited effect after one to two years of treatment, and early atropine studies showed a regression of the treatment effect once therapy has been discontinued. However, with atropine 0.01%, treatment effect is maintained after discontinuing treatment.10Related: Know the legal aspects of myopia control
Multifocal contact lenses have also been shown to be efficacious in slowing the progression of myopia, but at a lower efficacy rate compared to atropine 0.01%.8
In addition, orthokeratology remains a popular option for many practitioners. However, research evaluating the rate of myopia progression after discontinuing orthokeratology lenses shows more rapid increase in axial length compared to patients who have remained in spectacles.9
There is limited evidence to identify the ideal candidate for myopic progression treatment because all myopes do not progress at the same rate. Careful consideration should be given to parent/family goals for myopia progression treatment. Education regarding treatment outcomes, including continued need for correction for myopia even after treatment, and length of treatment needs to be addressed.
Childhood summary
Refractive errors in this age group can be treated as needed,with limited controversy, and annual exams can be the monitoring timeline of choice.
Myopia progression occurs in this age group, and while treating the progression in children may be controversial, these supplemental treatments may be an option for families who are educated about the risks and benefits and can also make an informed decision.
Related: Considering myopia control
Summary
Animal models of emmetropization have focused on inducing a refractive error and observing the animal’s physiologic response to this as the animal’s visual system tries to emmetropize by changing corneal curvature, axial length or lenticular thickness.3
When managing pediatric refractive errors, the emmetropization process looks far different. During the first 12 to 18 months of life, the infant visual system attempts to regulate the corneal curvature, lenticular thickness, and axial length to create a refractive error of low hyperopia. Prescribing glasses in this age group may disrupt the process but can save both visual and binocular development. Prescribing in this age group is not the same as inducing a refractive error in animal models.
In toddlers, there is limited evidence of an active process, and prescribing for moderate hyperopia, anisometropia, and astigmatism is necessary for vision and learning.
In childhood, myopia progression occurs, but there is limited understanding of which patients progress the most and which patients are the best candidates for myopia progression treatment. Family goals and discussion of outcomes may help determine who wishes to consider treatment.
Read more pediatric content here
About the author
Timothy E. Hug, OD, FAAO, is a pediatric optometrist and clinical associate professor of ophthalmology at University of Missouri-Kansas City School of Medicine is program director of the residency in pediatric optometry at Children’s Mercy Hospital in Kansas City, MO.
Dr. Hug graduated from the University of Houston College of Optometry. He is also program director of the residency in pediatric optometry at Children’s Mercy Hospital in Kansas City, MO. In his free time, he enjoys water sports and hanging out with his three children.
thug@cmh.edu
References:
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10. Chia A, Chua WH, Cheung YB, Wong WL, Lingham A, Fong A, Tan D. Atropine for the treatment of childhood myopia: safety and efficacy of 0.5%, 0.1%, and 0.01% doses (Atropine for the Treatment of Myopia 2). Ophthalmology. 2012 Feb;119(2):347-54.
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