Keys to IOL power selection in pseudophakic children

February 17, 2015

Highly variable myopia shifts can occur in pseudophakic children. IOL exchange seems to be an acceptable option for treating the high myopia that can develop with lens implantation in children.However, the use of IOLs in growing eyes remains controversial, and outcomes are uncertain because of lack of data, according to Courtney Kraus, MD.

Highly variable myopia shifts can occur in pseudophakic children. IOL exchange seems to be an acceptable option for treating the high myopia that can develop with lens implantation in children.

However, the use of IOLs in growing eyes remains controversial, and outcomes are uncertain because of lack of data, according to Courtney Kraus, MD.

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An important factor to consider is the selection of the optimal IOL power to implant in a specific child. However, understanding the ocular growth and development in pediatric patients is necessary to ensure selection of the correct IOL power, explained Dr. Kraus, Miles Center for Pediatric Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, and the Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.

During the early months of life, the axial length has been shown to increase with age, roughly 4 mm in one study of postnatal growth during the first year, and slower growth during the infantile and juvenile periods up to 13 years of age (Gordon RA, Donzls PB. Arch Ophthalmol. 1985;103:784-789).

“The progressive logarithmic increase after birth has significant impact on the postoperative refraction when an IOL of fixed power is implanted,” Dr. Kraus said. “Because of this, we adjust the targeted refractive outcome for IOL implantation in pediatric cataract patients based on age at the time of IOL implantation.”

 

By anticipating the myopic shift, she explained, its effect on the eventual refractive outcomes can be minimized by intentionally targeting undercorrection of the refractive error.

A range of myopic shifts has been reported and the variability is most difficult to predict in the youngest patients.

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“Several studies have reported the phenomenon of myopic shift in children who underwent cataract surgery before 2 years of age,” she said. “Without the ability to predict postoperative refraction with near certain, the safety and success of IOL exchange for highly myopic patients are important to establish.”

Retrospective study

Dr. Kraus and her colleagues conducted a retrospective chart review of patients over an 11-year period at the Storm Eye Institute to determine the preoperative characteristics and postoperative outcomes in children treated with IOL exchange due to myopic shift. No patients were included who underwent an IOL exchange procedure for IOL dislocation or decentration.

Retinoscopy and manifest refraction were used to obtain the refractive error. Patients were followed on postoperative day 1, week 1, month 1, and then at various intervals of at least every 6 months. The axial length was measured and keratometry was performed at least once annually.

Twenty eyes were found in the chart review to have undergone an IOL exchange. Of these, a myopic shift had developed in 15 eyes, and 10 of the 15 eyes had a unilateral cataract. The remaining 5 eyes represented cases with bilateral cataracts.

 

The average age at which a cataract was removed was 98.75 days. The IOL was removed an average of 6 years (range, 225 to 4,344 days) after the initial cataract surgery. The average spherical equivalent of the refractive error of the eyes that underwent an IOL exchange was -9.6 D, and after IOL exchange the average spherical equivalent of the refractive error was -1.3 D. The average axial length at the time of IOL exchange was 24 mm, and the average axial length in the unoperated fellow eye was 22.1 mm, a difference that reached significance (p < 0.005).

The amount of ocular growth of eyes from the time of the primary IOL implantation to IOL exchange was an average of 4.4 mm compared with 3.02 mm in the unoperated eyes, also a significant (p = 0.04) difference, she said.

Myopic shift

The number of members of the American Association for Pediatric Ophthalmology and Strabismus who have reported implanting an IOL in children less than 2 years of age has increased markedly, 13-fold, between 1993 and 2001, Dr. Kraus pointed out.

The Infant Aphakia Treatment Study Group reported in 2012 that there was no difference in visual outcomes between the eyes of children with an IOL and eyes that were aphakic after undergoing surgery for unilateral congenital cataracts. The study group concluded that “selective use of IOLs was acceptable, specifically in cases in which situations made it challenging to anticipate contact lens compliance.”

“Regarding the increase in IOL use in young patients, we can expect to encounter an increasing number of children with high degrees of myopia,” Dr. Kraus said. “Age at the time of surgery is one factor that can lead to an expected myopic shift. Patients younger than 2 years of age particularly have had large myopic shifts. The current results and those of other studies of pseudophakic children support this.”

 

Besides patient age, anisometropic amblyopia is another factor in myopic shift. Previous studies have reported that excessive axial elongation resulting from amblyopia is responsible for the myopic shift, she explained.

“However, this theory is challenged when we see that studies have reported that myopic shifts occur even in those with good vision of 20/40 or higher,” she said. In the study under discussion, significant myopia developed in four patients with good vision.

High myopic shifts develop only in unilateral pseudophakic patients, despite other studies that have suggested minimal myopic shifts should occur in patients with binocular implants, Dr. Kraus reported.

“Presumably in bilateral pseudophakia the eyes should grow similarly,” she said. “However, in the current study, large asymmetric myopic shifts were seen in patients with bilateral IOL implantation. Five of the 15 study patients had bilateral pseudophakia and only one eye had a large myopic shift.”

On the study’s main findings, Dr. Kraus said, “While the goal of IOL implantation in pediatric patients should be to anticipate and compensate for the myopic shift that occurs using intentional hyperopia, individual variability can still lead to a myopic surprise.

“Unless we can predict with near certainty the postoperative refractive change, there is tremendous value in being able to perform an IOL exchange to correct high myopia,” she continued. “IOL exchange can be performed across a range of ages and times after cataract extraction and IOL implantation, making it an acceptable option for treating high myopia in these patients.”