Common misconception: a glasses prescription isn't a finite, objective number. We don't use a machine to measure your eye and spit a number that's immutable and definite -- if we did it wouldn't look that great to you, the wearer. The visual system is so complex, involving not just the eye itself but the muscles in and around the eye and the visual cortex of the brain, that a measurement of the eye is just one component to a successful glasses prescription. When prescribing for children, doctors are at a distinct disadvantage because the subjective responses of the patient can be unreliable or just plain unusable. Some kids are shy; some are scared; some really, really, really want glasses. The latter are one of the most challenging because as a concerned parent you might worry something must be horribly wrong; your child can't even see the big E! And then of course the doctor tells you "nope all fine, no glasses here" to the wail of your child's disappointment. Today we're talking the art of prescribing for kids -- when to prescribe, what to prescribe, and how to get kids that need glasses wearing them!
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Don't Under Minus
Parents often worry that their child's prescription is changing too fast, and some may even ask the doctor to cut back their child's Rx so it's not "too strong." But a prescription that is under minused in school aged children (made weaker on purpose) is much worse for the developing eye than one that corrects vision clearly. A 2002 study proved that undercorrecting near sighted children by +0.75D caused their eyes to worsen faster than if they were prescribed their full strength prescription. Scientists theorize that the presence of any blurred vision causes children's eyes to change at a faster speed. Prescribing the full amount to achieve 20/20 vision in near sighted (myopic) school-aged children is the best approach. Remind parents that if their child complains of changing vision in 6 months, go ahead and schedule a follow-up appointment to get things rechecked. It's better to adjust their glasses mid year to achieve clarity than to let them go another 6 months with blurry vision with that risk of accelerated rate of myopic progression. For more on myopia control check this post.
Don't Over Plus
It's normal for especially young children to be farsighted (hyperopic). Studies show the average newborn has just over 2.00D of hyperopia and the average 2 year old has just over 1.00D. The range of acceptable variability where a child would still be expected to have normal visual function is wide. When to prescribe?
For 1- 4 year old patients prescribe if Rx > +3.50 D; Cut Rx by 1.00D
For 4-5 year old patients prescribe if Rx > +2.50 D; Cut Rx for 1.00D
For 6 and up prescribe if Rx > +1.50 D or if pt is symptomatic; no cut in Rx necessary
It's important to cut back the prescription in young hyperopic patients to encourage the chance that the patient's eyes will normalize to zero as they continue to grow (called emmetropization). By age 6 research suggests emmetropization is pretty much over, which is why you no longer have to cut the Rx down. As a general rule, a school aged child with great visual acuity, normal binocular and accommodative function and no complaints is likely doing great without glasses, even if they have a low hyperopic prescription.
Correcting Astigmatism
There are few things in vision more normal than astigmatism. In fact, 69% of infants are born with over 1.00D of astigmatism. Most kids born with astigmatism undergo rapid improvement by the time they are four years of age, so prescribing for astigmatism in young children is not usually necessary. If astigmatism is still present by school age years, however, it can begin to have a big impact on classroom performance. A 2016 study showed that correcting the prescription of kids with high amounts of astigmatism (3.00D or more) immediately improved their reading fluency by an average of one grade level.
For patients under 2 prescribe if astigmatism > 2.50 D; Cut cylinder Rx by 50%
For 2-4 year old patients prescribe if astigmatism > 2.00 D; Cut cylinder Rx by 50%
For 5 and up prescribe if astigmatism > 1.50 D or if pt is symptomatic with lower astigmatism; no cut in Rx necessary
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| Astigmatism can make it difficult to distinguish letters or numbers, especially in higher grade levels where the font size gets smaller. via |
Exception to these rules: when the eyes have big differences in their prescription (called anisometropia) and amblyopia (lazy eye) or strabismus (eye turn) is developing, then prescribing the full amount of prescription even in very young children becomes important to achieving the best possible outcome.
Check for Accommodative Dysfunction
It's easy to think a child that has no prescription but won't read the chart is malingering (the polite doctor term for faking it). Glasses these days are the cool thing to have, and sometimes when a child's friend gets glasses it becomes mission number one for your child to have glasses too. But sometimes a child might have no real distance vision issue but won't be able to read the chart for a true medical reason. I always do a quick and easy accommodative test (NRA/PRA is a go to for responsive kids - MEM Retinoscopy on younger) to rule out accommodative dysfunction. If a child has accommodative dysfunction, they won't be able to see clearly in the distance because their focusing system is "locked up" at near. Their eyes won't be able to adjust back and forth between distance and up close, so distance looks blurry. Referral for vision therapy is a great solution for kids suffering from this issue, and sometimes progressive glasses can help the eyes adjust more easily from near to far.
When to prescribe progressives for myopes? For a few years it was a commonly discussed theory that prescribing progressive glasses for near sighted children could help reduce how quickly their vision worsened year to year. The COMET study proved that prescribing progressive or bifocal glasses for controlling nearsightedness had no benefit in children with normal focusing systems -- prescribing progressive glasses in a normal nearsighted child did NOT slow down the worsening of their myopia. But in myopic children that have accommodative dysfunction, progressive glasses do help. Prescribing for the right patient can make a difference.
Don't Forget Safety and Sun Protection
Did you know that kids are the most at risk for ocular sun damage? In fact 25% of the sun damage that occurs in a person's lifetime happens before age 18. Sun damage in the eye is responsible for potentially fatal conditions like ocular melanoma, but also diseases of the eye we associate with aging like cataracts and macular degeneration. Those conditions don't develop due to the sun damage we get when we're 80; they're a result of the sun damage we started getting as children. That's why prescribing sun protection in children's glasses is so important. Transitions lenses allow kid's glasses to be 100% UVA and UVB protective without kids having to keep track of multiple pairs -- a win for kids and parents both.
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| A huge trend in kids eyewear the last few years is wearing rec specs for full time glasses wear. The sporty appearance make kids feel more confident than the traditional round metal frames many kids get fit in with dread. photo via |
Another major risk for children's eyesight is injury, especially if they play sports. 90% of all blinding sports-related eye injuries in America could be prevented if the child had been wearing protective eyewear. Shatter resistant lens materials like polycarbonate and trivex are essential for kid's glasses both on and off the field to protect the eye from potential injury.
And don't underestimate the way that a child's self esteem can be tied to their perceived appearance. I always encourage parents to let their child lead the selection process for their glasses when they enter school age years. Their glasses need to be a part of their identity that they like; not only will the chance that they actually wear their glasses go way up, but higher self esteem is associated with higher academic performance as well!
