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Multiple measurements can reduce errors in calculating pediatric IOL power
Review of recent literature advocates immersion A-scan biometry and parental involvement.
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In the continuing refinement of surgical techniques for cataract extraction in children, determining the appropriate IOL power remains problematic. Careful preoperative measurements can help reduce prediction error, according to a study.
“Intraocular lenses can now be safely implanted in infants and young children,” Mary A. O’Hara, MD, FACS, FAAP, told Ocular Surgery News.
Still, formulas for IOL power calculations derive primarily from adult studies that fail to account for children’s unique ocular anatomy.
“Increasing the accuracy of corneal curvature, anterior chamber depth and axial length measurements helps increase the accuracy of IOL power calculation,” O’Hara said. “Repeat measurements are helpful when the power calculation does not add up.”
Mary A. O’Hara
O’Hara is the author of a recent literature review on pediatric IOL power calculations that was published in Current Opinion in Ophthalmology.
Multiple formulas
No single IOL power calculation formula is consistently accurate, so several different formulas should be used to decrease variance and increase accuracy, O’Hara said.
“[Because axial length measurements] are a significant source of error in IOL power calculation, anything that increases accuracy of this measurement is exciting, particularly in pediatric eyes,” she said.
In children, an inaccurate axial length measurement can account for 4 D to 14 D or more for each millimeter difference in IOL power, as opposed to 3 D to 4 D in adults.
A-scan ultrasound biometry using the applanation method can indent the supple pediatric cornea, inducing measurement artifacts in the form of shorter axial lengths and shallower anterior chamber depth measurements, O’Hara said. In contrast, the immersion technique uses a coupling fluid between the cornea and the probe to reduce corneal indentation, providing a more accurate measurement of axial length and anterior chamber depth.
In the review, O’Hara noted that targeting a refractive goal in children continues to be controversial; however, low degrees of hyperopia do not appear to adversely impact long-term visual acuity.
“When the fellow eye is emmetropic, I aim for a low degree of hyperopia in my pseudophakic patients,” she said. “Indeed, most of my young patients evidence a low degree of hyperopia in the cycloplegic refraction of their non-cataractous eye. My postoperative refractive target usually matches that refraction.”
Parent involvement
Parental buy-in is essential for the success of pediatric cataract surgery.
“The care of the child with cataract always begins with a conversation with the parents,” O’Hara said.
The postop care and follow-up of the pediatric cataract patient is time-consuming and can be problematic if parents do not follow through on the plan. The bulk of responsibility for postoperative rehabilitation — adherence to postop restrictions, amblyopia therapy and spectacle use — falls to parents, and their concerns and capabilities are weighed heavily in the decision about whether to implant an IOL, O’Hara said.
“We tell parents that the surgery is the easy part,” she said.
In addition, reasonable expectations for surgical outcomes must be established.
In the pipeline
Adjustable IOLs may be a promising avenue for refining the accuracy of IOL power calculations, O’Hara said.
“However, it remains to be seen whether the initial studies in adults will translate to children,” she said.
Combining a permanent IOL and temporary piggyback IOL, which is removed once a myopic shift occurs, has also been proposed in children. – by Bob Kronemyer